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{{Short description|Progressive neurodegenerative disease}}
{{Redirect2|Parkinson's|Parkinson's Disease|the medical journal|Parkinson’s Disease (journal)|other uses}}
{{Redirect|Parkinson's|the medical journal|Parkinson's Disease (journal)|other uses}}
{{pp-semi-indef}}
{{Cs1 config|name-list-style=vanc|display-authors=6}}
{{short description|Long-term degenerative neurological disorder}}
{{Use dmy dates|date=August 2020}} {{Use dmy dates|date=July 2024}}
{{Infobox medical condition (new) {{Infobox medical condition
| name = Parkinson's disease | name = Parkinson's disease
| synonyms = Parkinson disease, idiopathic or primary parkinsonism, hypokinetic rigid syndrome, paralysis agitans, shaking palsy | synonyms = Idiopathic or primary parkinsonism, hypokinetic rigid syndrome, paralysis agitans, shaking palsy
| image = {{Multiple image|perrow = 2|total_width=300|align=center|image_gap=10
| image = Paralysis agitans (1907, after St. Leger).png
| border = infobox
| caption = Illustration of Parkinson's disease by ], first published in ''A Manual of Diseases of the Nervous System'' (1886)
| image_style = border:none;
| alt = Two sketches (one from the front and one from the right side) of a man, with an expressionless face. He is stooped forward and is presumably having difficulty walking.
| image1 = Parkinson’s disease 1880s.jpg
| field = ]
| caption1 = A. 1880s illustration of Parkinson's disease (PD)
| symptoms = ], ], ], ]<ref name=NIH2016/>
| image2 = Mild motor-predominant PD.jpg
| complications = ], ], anxiety<ref name=Sv2016/>
| caption2 = B. Mild motor-predominant PD
| onset = Age over 60<ref name=NIH2016/><ref name=Car2016/>
| image3 = Intermediate PD.jpg
| duration =
| caption3 = C. Intermediate PD
| causes = Unknown<ref name=Lancet2015/>
| image4 = Diffuse malignant PD.jpg
| risks = ] exposure, ]<ref name=Lancet2015/>
| caption4 = D. Diffuse malignant PD
| diagnosis = Based on symptoms<ref name=NIH2016/>
| footer =
| differential = ], ], ], ] use<ref>{{cite book|vauthors= Ferri FF|title=Ferri's differential diagnosis : a practical guide to the differential diagnosis of symptoms, signs, and clinical disorders|date=2010|publisher=Elsevier/Mosby|location=Philadelphia, PA|isbn=978-0323076999|chapter=Chapter P|edition=2nd}}</ref>
}}
| prevention =
| symptoms = {{Unbulleted list|Main: ], ], ], ] (collectively known as ])|Other: ], ], ], ]}}
| treatment = Medications, surgery<ref name=NIH2016/>
| complications = ], ], ]
| medication = ], ]s<ref name=Sv2016/>
| onset = Age over 60{{sfn|National Institute of Neurological Disorders and Stroke}}
| prognosis = ] about 7–15 years <ref name=Macleod2014>{{cite journal | vauthors = Macleod AD, Taylor KS, Counsell CE | title = Mortality in Parkinson's disease: a systematic review and meta-analysis | journal = Movement Disorders | volume = 29 | issue = 13 | pages = 1615–22 | date = November 2014 | pmid = 24821648 | doi = 10.1002/mds.25898 | doi-access = free }}</ref>
| duration = Long-term
| frequency = 6.2 million (2015)<ref name=GBD2015Pre/>
| causes =
| deaths = 117,400 (2015)<ref name=GBD2015De/>
| risks = Family history, ], ], ] exposure, ]
| diagnosis = Symptomatic, ]
| differential = ], ], ], ] use,{{Sfn|Ferri|2010|loc= Chapter P}} ], ], ], ]{{sfn|Koh|Ito|2017}}
| prevention = Physical activity, ], ]
| treatment = ], ]
| medication = ], ]s, ], ]s, ]s
| prognosis = Near-normal life expectancy
| frequency = 8.5&nbsp;million (2019){{sfn|Ou|Pan|Tang|Duan|2021}}
| named after = ]
}} }}
'''Parkinson's disease''' ('''PD'''), or simply '''Parkinson's''' <ref name="PF">{{cite web |title=Understanding Parkinson's |url=https://www.parkinson.org/understanding-parkinsons |website=Parkinson's Foundation |access-date=12 August 2020 |language=en}}</ref> is a long-term ] of the ] that mainly affects the ]. The symptoms usually emerge slowly and, as the disease worsens, non-motor symptoms become more common.<ref name=NIH2016/><ref name=Lancet2015>{{cite journal | vauthors = Kalia LV, Lang AE | s2cid = 5502904 | title = Parkinson's disease | journal = Lancet | volume = 386 | issue = 9996 | pages = 896–912 | date = August 2015 | pmid = 25904081 | doi = 10.1016/s0140-6736(14)61393-3 }}</ref> The most obvious early symptoms are ], ], ], and ]<ref name=NIH2016/>. ] and behavioral problems may also occur with ], ], and ] occurring in many people with PD.<ref name=":5" /> ] becomes common in the advanced stages of the disease. Those with Parkinson's can also have problems with their ] and sensory systems.<ref name=NIH2016/><ref name="Sv2016">{{cite journal|vauthors=Sveinbjornsdottir S|date=October 2016|title=The clinical symptoms of Parkinson's disease|journal=Journal of Neurochemistry|volume=139 Suppl 1|pages=318–24|doi=10.1111/jnc.13691|pmid=27401947|doi-access=free}}</ref> The motor symptoms of the disease result from the ] in the ], a region of the ], leading to a ] deficit.<ref name="NIH2016" /> The cause of this cell death is poorly understood, but involves the build-up of ]s into ] in the ]s.<ref name=":9" /><ref name="Lancet2015" /> Collectively, the main motor symptoms are also known as "]" or a "parkinsonian syndrome".<ref name="Lancet2015" />


<!-- Definition and symptoms -->
The cause of PD is ], with both ] and environmental factors being believed to play a role.<ref name="Lancet2015" /> Those with a family member affected by PD are at an increased risk of getting the disease, with certain genes known to be inheritable risk factors.<ref name="Quadri2018" /> Other risk factors are those who have been exposed to certain ] and who have prior ]. ] and ] and ] drinkers are at a reduced risk.<ref name=Lancet2015/><ref>{{cite journal | vauthors = Barranco Quintana JL, Allam MF, Del Castillo AS, Navajas RF | s2cid = 26605333 | title = Parkinson's disease and tea: a quantitative review | journal = Journal of the American College of Nutrition | volume = 28 | issue = 1 | pages = 1–6 | date = February 2009 | pmid = 19571153 | doi = 10.1080/07315724.2009.10719754 }}</ref>
'''Parkinson's disease''' ('''PD'''), or simply '''Parkinson's''', is a ] primarily of the ], affecting both ] and non-motor systems. Symptoms typically develop gradually, with non-motor issues becoming more prevalent as the disease progresses. Common motor symptoms include ]s, ] (slowness of movement), ], and ], collectively termed ]. In later stages, ], ], and ] such as ], ], ]s, or ] may arise.


<!-- Causes and pathophysiology -->
Diagnosis of typical cases is mainly based on symptoms, with motor symptoms being the chief complaint. Tests such as ] (] or imaging to look at dopamine neuronal dysfunction known as ]) can be used to help rule out other diseases.<ref name=":1" /><ref name=NIH2016/> Parkinson's disease typically occurs in people over the age of 60, of whom about one percent are affected.<ref name=NIH2016/><ref name=Car2016>{{cite book|vauthors=Carroll WM|title=International Neurology|date=2016|publisher=John Wiley & Sons|isbn=978-1118777367|page=188|url=https://books.google.com/books?id=mRl6DAAAQBAJ&pg=PA188|url-status=live|archive-url=https://web.archive.org/web/20170908154209/https://books.google.com/books?id=mRl6DAAAQBAJ&pg=PA188|archive-date=8 September 2017}}</ref> Males are more often affected than females at a ratio of around 3:2.<ref name=Lancet2015/> When it is seen in people before the age of 50, it is called early-onset PD.<ref>{{cite book |vauthors=Mosley AD |title=The encyclopedia of Parkinson's disease |date=2010 |publisher=Facts on File |location=New York |isbn=978-1438127491 |page=89 |edition=2nd |url= https://books.google.com/books?id=tE6VgburpxkC&pg=PA89 |url-status=live |archive-url=https://web.archive.org/web/20170908154209/https://books.google.com/books?id=tE6VgburpxkC&pg=PA89 |archive-date=8 September 2017 }}</ref> In 2015, PD affected 6.2 million people and resulted in about 117,400 deaths globally.<ref name=GBD2015Pre>{{cite journal | title = Global, regional, and national incidence, prevalence, and years lived with disability for 310 diseases and injuries, 1990–2015: a systematic analysis for the Global Burden of Disease Study 2015 | journal = Lancet | volume = 388 | issue = 10053 | pages = 1545–1602 | date = October 2016 | pmid = 27733282 | pmc = 5055577 | doi = 10.1016/S0140-6736(16)31678-6 | author1 = GBD 2015 Disease Injury Incidence Prevalence Collaborators }}</ref><ref name=GBD2015De>{{cite journal | title = Global, regional, and national life expectancy, all-cause mortality, and cause-specific mortality for 249 causes of death, 1980–2015: a systematic analysis for the Global Burden of Disease Study 2015 | journal = Lancet | volume = 388 | issue = 10053 | pages = 1459–1544 | date = October 2016 | pmid = 27733281 | pmc = 5388903 | doi = 10.1016/s0140-6736(16)31012-1 | author1 = GBD 2015 Mortality Causes of Death Collaborators }}</ref> The average ] following diagnosis is between 7 and 15 years.<ref name=Sv2016/>
Most cases of Parkinson's disease are ], though contributing factors have been identified. Pathophysiology involves progressive ] in the ], a ] region that provides ] to the ], a system involved in voluntary ]. The cause of this cell death is poorly understood but involves the aggregation of ] into ] within ]s. Other potential factors involve ] and environmental influences, medications, lifestyle, and prior health conditions.


<!-- Diagnosis and epidemiology -->
There is no cure for PD; treatment aims to improve the symptoms.<ref name=NIH2016>{{cite web|title=Parkinson's Disease Information Page|url=https://www.ninds.nih.gov/Disorders/All-Disorders/Parkinsons-Disease-Information-Page|website=NINDS|access-date=18 July 2016|date=30 June 2016}}</ref><ref name="pmid15172778">{{cite journal|vauthors=Samii A, Nutt JG, Ransom BR|date=May 2004|title=Parkinson's disease|url=https://zenodo.org/record/1259791|journal=Lancet|volume=363|issue=9423|pages=1783–93|doi=10.1016/S0140-6736(04)16305-8|pmid=15172778|s2cid=35364322}}</ref> ] is typically with the medications levodopa (]), ], or ].<ref name=":1" /> As the disease progresses, these medications become less effective, while at the same time producing a ] marked by ].<ref name=Sv2016/> At that time, medications may be used in combination and doses may be increased.<ref name=":1" /> Diet and certain forms of rehabilitation have shown some effectiveness at improving symptoms.<ref name="pmid19691125">{{cite journal | vauthors = Barichella M, Cereda E, Pezzoli G | title = Major nutritional issues in the management of Parkinson's disease | journal = Movement Disorders | volume = 24 | issue = 13 | pages = 1881–92 | date = October 2009 | pmid = 19691125 | doi = 10.1002/mds.22705 | hdl = 2434/67795 | s2cid = 23528416 | hdl-access = free }}</ref><ref name=Neuro2011>{{cite journal | vauthors = Ahlskog JE | title = Does vigorous exercise have a neuroprotective effect in Parkinson disease? | journal = Neurology | volume = 77 | issue = 3 | pages = 288–94 | date = July 2011 | pmid = 21768599 | pmc = 3136051 | doi = 10.1212/wnl.0b013e318225ab66 }}</ref> ] to place ]s for ] has been used to reduce motor symptoms in severe cases where drugs are ineffective.<ref name=NIH2016/> Evidence for treatments for the non-movement-related symptoms of PD, such as sleep disturbances and emotional problems, is less strong.<ref name=Lancet2015/>
Diagnosis is primarily based on ], typically motor-related, identified through ]. ] like ] can support the diagnosis. Parkinson's typically manifests in individuals over 60, with about one percent affected. In those younger than 50, it is termed "early-onset PD".

<!-- Treatment and prognosis -->
No cure for Parkinson's is known, and treatment focuses on alleviating symptoms. Initial treatment typically includes ], ]s, or ]s. As the disease progresses, these medications become less effective and may cause ]. Diet and rehabilitation therapies can help improve symptoms. ] is used to manage severe motor symptoms when drugs are ineffective. There is little evidence for treatments addressing non-motor symptoms, such as sleep disturbances and mood instability. Life expectancy for those with PD is near-normal but is decreased for early-onset.


The disease is named after the English doctor ], who published the first detailed description in ''An Essay on the Shaking Palsy'', in 1817.<ref name= ParkinsonJEssay>{{cite book | vauthors= Parkinson J | date = 1817 | publisher = Whittingham and Roland for Sherwood, Neely, and Jones | location = London |url=http://www.gutenberg.org/files/23777/23777-h/23777-h.htm |title=An Essay on the Shaking Palsy |url-status=live |archive-url=https://web.archive.org/web/20150924210730/http://www.gutenberg.org/files/23777/23777-h/23777-h.htm |archive-date=24 September 2015 }}</ref><ref>{{cite journal | vauthors = Shulman JM, De Jager PL, Feany MB | s2cid = 8328666 | title = Parkinson's disease: genetics and pathogenesis | journal = Annual Review of Pathology | volume = 6 | pages = 193–222 | date = February 2011 | pmid = 21034221 | doi = 10.1146/annurev-pathol-011110-130242 | orig-year = 25 October 2010 }}</ref> Public awareness campaigns include World Parkinson's Day (on the birthday of James Parkinson, 11 April) and the use of a red ] as the symbol of the disease.<ref name="pmid18175393">{{cite journal | vauthors = Lees AJ | title = Unresolved issues relating to the shaking palsy on the celebration of James Parkinson's 250th birthday | journal = Movement Disorders | volume = 22 Suppl 17 | issue = Suppl 17 | pages = S327–34 | date = September 2007 | pmid = 18175393 | doi = 10.1002/mds.21684 | s2cid = 9471754 }}</ref> People with Parkinson's who have increased the public's awareness of the condition include the boxer ], actor ], Olympic cyclist ], and actor ].<ref name="MJF_TIME">{{cite news| url=http://www.time.com/time/specials/2007/time100/article/0,28804,1595326_1615754_1615882,00.html| title=Michael J. Fox| date=3 May 2007| vauthors = Davis P| work=The TIME 100| publisher=]| access-date=2 April 2011| url-status=live| archive-url=https://web.archive.org/web/20110425013526/http://www.time.com/time/specials/2007/time100/article/0,28804,1595326_1615754_1615882,00.html| archive-date=25 April 2011| df=dmy-all}}</ref><ref name=Mac2008>{{cite news |last=Macur |first=Juliet | name-list-style = vanc |title=For the Phinney Family, a Dream and a Challenge |url= https://www.nytimes.com/2008/03/26/sports/othersports/26cycling.html?pagewanted=all&_r=0 |newspaper=The New York Times |access-date=25 May 2013 |date=26 March 2008|quote=About 1.5 million Americans have received a diagnosis of Parkinson's disease, but only 5 to 10 percent learn of it before age 40, according to the National Parkinson Foundation. Davis Phinney was among the few. |url-status=live |archive-url= https://web.archive.org/web/20141106025145/http://www.nytimes.com/2008/03/26/sports/othersports/26cycling.html?pagewanted=all&_r=0 |archive-date=6 November 2014}}</ref><ref name="Ali_NN_comment">{{cite journal|url=http://www.aan.com/elibrary/neurologynow/?event=home.showArticle&id=ovid.com:/bib/ovftdb/01222928-200602020-00003 |title=Muhammad Ali's Message: Keep Moving Forward |date=April 2006 |journal=Neurology Now | vauthors = Brey RL |volume=2 |issue=2 |page=8 |doi=10.1097/01222928-200602020-00003 |url-status=dead |archive-url= https://web.archive.org/web/20110927022505/http://www.aan.com/elibrary/neurologynow/?event=home.showArticle&id=ovid.com%3A%2Fbib%2Fovftdb%2F01222928-200602020-00003 |archive-date=27 September 2011 |access-date= 22 August 2020}}</ref><ref>{{cite news |last1=Alltucker |first1=Ken | name-list-style = vanc |title=Alan Alda has Parkinson's disease: Here are 5 things you should know |url=https://www.usatoday.com/story/news/nation/2018/07/31/alan-alda-has-parkinsons-disease-5-things-know/871265002/ |access-date=6 May 2019 |agency=USA Today |date=31 July 2018}}</ref>
{{TOC limit}} {{TOC limit}}


==Classification== ==Classification and terminology==
{{See also|Parkinsonism|Parkinson-plus syndrome}}
Parkinson's disease is the most common form of ] and is sometimes called "idiopathic parkinsonism", meaning parkinsonism with no identifiable cause.<ref name="pmid15172778"/><ref name="Jankovic_book-Epidemiology2">{{cite book|last=Schrag|first=Anette|title=Parkinson's disease and movement disorders|publisher=Lippincott Williams & Wilkins|year=2007|isbn=978-0-7817-7881-7|veditors=Tolosa E, Jankovic JJ|location=Hagerstown, Maryland|pages=50–66|chapter=Epidemiology of movement disorders}}</ref> Scientists sometimes refer to Parkinson’s disease as a type of neurodegenerative disease called ] due to an abnormal accumulation of the protein ] in the brain.<ref name="pmid164896092" /> The synucleinopathy classification distinguishes Parkinson's disease from other neurodegenerative diseases, such as ], where the brain accumulates a different protein known as the ].<ref name="pmid164896092">{{cite journal|vauthors=Galpern WR, Lang AE|date=March 2006|orig-year=17 February 2006|title=Interface between tauopathies and synucleinopathies: a tale of two proteins|journal=Annals of Neurology|volume=59|issue=3|pages=449–58|doi=10.1002/ana.20819|pmid=16489609|s2cid=19395939}}</ref>
Parkinson's disease (PD) is a ] affecting both the ] and ], characterized by the ] of ]-producing ] in the ] region of the brain.{{Sfn|Ramesh|Arachchige|2023|pp=200–201, 203}} It is classified as a ] due to the abnormal accumulation of the protein ], which aggregates into ] within affected neurons.{{Sfn|Calabresi|Mechelli|Natale|Volpicelli-Daley|2023|pp=1,5}}


The loss of dopamine-producing neurons in the substantia nigra initially presents as movement abnormalities, leading to Parkinson's further categorization as a ].{{Sfn|National Institute of Neurological Disorders and Stroke}} In 30% of cases, disease progression leads to the cognitive decline known as ] (PDD).{{Sfn|Wallace|Segerstrom|van Horne|Schmitt|2022|p=149}} Alongside ], PDD is one of the two subtypes of ].{{Sfn|Hansen|Ling|Lashley|Holton|2019|p=635}}
Considerable clinical and pathological overlap exists between ] and synucleinopathies, however there are also differences. In contrast to Parkinson's disease, people with Alzheimer's disease most commonly experience memory loss. The cardinal signs of Parkinson's disease (slowness, tremor, stiffness, and postural instability) are not normal features of Alzheimer's.


The four cardinal motor symptoms of Parkinson's—] (slowed movements), ], ], and ]—are called ].{{Sfn|Bhattacharyya|2017|p=7}}{{Sfn|Stanford University School Medicine}} These four symptoms are not exclusive to Parkinson's and can occur in many other conditions,{{Sfn|Bologna|Truong|Jankovic|2022|pp=1–6}}{{Sfn|Limphaibool|Iwanowski|Holstad|Kobylarek|2019|pp=1–2}} including ] and ].{{Sfn|Leta|Urso|Batzu|Lau|2022|p=1122}}{{Sfn|Langston|2017|p=S11}} Neurodegenerative diseases that feature parkinsonism but have distinct differences are grouped under the umbrella of ] or, alternatively, atypical parkinsonian disorders.{{Sfn|Prajjwal|Kolanu|Reddy|Ahmed|2024|pp=1–3}}{{Sfn|Olfatia|Shoeibia|Litvanb|2019|p=101}} Parkinson's disease can be attributed to ] or be ], in which there is no clearly identifiable cause. The latter, also called ] Parkinson's, makes up some 85–90% of cases.{{Sfn|Dolgacheva|Zinchenko|Goncharov|2022|p=2}}
Attempts to classify Parkinson's disease into different subtypes have been made, with focus put on age of onset, progression of symptoms, and dominance of tremor. None have currently been widely adopted as a complete model.<ref>{{Cite journal|last=Marras|first=C.|last2=Lang|first2=A.|date=2013-04-01|title=Parkinson's disease subtypes: lost in translation?|url=https://jnnp.bmj.com/lookup/doi/10.1136/jnnp-2012-303455|journal=Journal of Neurology, Neurosurgery & Psychiatry|language=en|volume=84|issue=4|pages=409–415|doi=10.1136/jnnp-2012-303455|issn=0022-3050|doi-access=free}}</ref>


==Signs and symptoms== ==Signs and symptoms==
]
|quote=The strokes forming the letters are very irregular and sinuous, whilst the irregularities and sinuosities are of a very limited width. (...) the down-strokes are all, with the exception of the first letter, made with comparative firmness and are, in fact, nearly normal – the finer up-strokes, on the contrary, are all tremulous in appearance (...).}}</ref>|alt=French signature reads "Catherine Metzger 13 Octobre 1869"]]
{{Main|Signs and symptoms of Parkinson's disease}} {{Main|Signs and symptoms of Parkinson's disease}}
The most recognizable symptoms in Parkinson's disease are movement ("motor") related.<ref name=Jankovic2008/> Non-motor symptoms, which include ] dysfunction, ] problems (mood, cognition, behavior or thought alterations), and sensory (especially altered sense of smell) and sleep difficulties, are also common. Some of these non-motor symptoms may be present at the time of diagnosis.<ref name=Jankovic2008/>

===Motor=== ===Motor===
{{Further|Parkinsonism}} {{See also|Parkinsonism}}
{{multiple image
Four motor symptoms are considered ] in PD: tremor, slowness of movement (bradykinesia), rigidity, and postural instability.<ref name=Jankovic2008>{{cite journal | vauthors = Jankovic J | title = Parkinson's disease: clinical features and diagnosis | journal = Journal of Neurology, Neurosurgery, and Psychiatry | volume = 79 | issue = 4 | pages = 368–76 | date = April 2008 | pmid = 18344392 | doi = 10.1136/jnnp.2007.131045 | url = http://jnnp.bmj.com/content/79/4/368.full | archive-url = https://web.archive.org/web/20150819084941/http://jnnp.bmj.com/content/79/4/368.full | df = dmy-all | url-status=live | archive-date = 19 August 2015 | doi-access = free }}</ref>
| align = right
| direction = vertical
| total_width = 220
| image1 = Paralysis agitans-Male Parkinson's victim-1892 cropped.png
| image2 = Writing by a Parkinson's disease patient.png
| footer = Motor symptoms include a stooping posture, the "]", and ]—jagged, diminutive handwriting.
}}


Although a wide spectrum of motor and non-motor symptoms appear in Parkinson's, the cardinal features remain tremor, bradykinesia, rigidity, and postural instability, collectively termed parkinsonism.{{sfn|Abusrair|Elsekaily|Bohlega|2022|p=2}} Appearing in 70–75 percent of PD patients,{{sfn|Abusrair|Elsekaily|Bohlega|2022|p=2}}{{sfn|Moustafa|Chakravarthy|Phillips|Gupta|2016|p=730}} tremor is often the predominant motor symptom.{{sfn|Abusrair|Elsekaily|Bohlega|2022|p=2}} Resting tremor is the most common, but kinetic tremors—occurring during voluntary movements—and postural tremor—preventing upright, stable posture—also occur.{{sfn|Moustafa|Chakravarthy|Phillips|Gupta|2016|p=730}} Tremor largely affects the hands and feet:{{sfn|Moustafa|Chakravarthy|Phillips|Gupta|2016|p=730}} a classic parkinsonian tremor is "]", a resting tremor in which the thumb and index finger make contact in a circular motion at 4–6 Hz frequency.{{sfn|Abusrair|Elsekaily|Bohlega|2022|p=4}}{{sfn|Sveinbjornsdottir|2016|p=319}}
The most common presenting sign is a coarse slow ] of the hand at rest which disappears during voluntary movement of the affected arm and in the deeper stages of sleep.<ref name=Jankovic2008/> It typically appears in only one hand, eventually affecting both hands as the disease progresses.<ref name=Jankovic2008/> Frequency of PD tremor is between 4 and 6 ] (cycles per second). A feature of tremor is ''pill-rolling'', the tendency of the index finger and thumb to touch and perform together a circular movement.<ref name=Jankovic2008/><ref name="Cooper"/> The term derives from the similarity between the movement of people with PD and the early pharmaceutical technique of manually making pills.<ref name="Cooper">{{cite book | vauthors = Cooper G, Eichhorn G, Rodnitzky RL |chapter=Parkinson's disease | veditors = Conn PM | title=Neuroscience in medicine|publisher=Humana Press|location=Totowa, NJ|year=2008 |pages= 508–12|isbn=978-1-60327-454-8}}</ref>


Bradykinesia describes difficulties in ], beginning, and executing, resulting in overall slowed movement with reduced amplitude that affects sequential and simultaneous tasks.{{sfn|Bologna|Paparella|Fasano|Hallett|2019|pp=727-729}} Bradykinesia can also lead to ], reduced facial expressions.{{sfn|Sveinbjornsdottir|2016|p=319}} ], also called rigor, refers to a feeling of stiffness and resistance to passive stretching of muscles that occurs in up to 89 percent of cases.{{sfn|Ferreira-Sánchez|Moreno-Verdú|Cano-de-la-Cuerda|2020|p=1}}{{sfn|Moustafa|Chakravarthy|Phillips|Gupta|2016|p=728}} ] typically appears in later stages, leading to ] and ].{{sfn|Palakurthi|Burugupally|2019|pp=1-2}} Postural instability also leads to a forward stooping posture.{{sfn|Palakurthi|Burugupally|2019|pp=1,4}}
] (slowness of movement) is found in every case of PD, and is due to disturbances in ] of movement initiation, and associated with difficulties along the whole course of the movement process, from planning to initiation to execution of a movement. Performance of sequential and simultaneous movement is impaired. Bradykinesia is the most handicapping symptom of Parkinson’s disease leading to difficulties with everyday tasks such as dressing, feeding, and bathing. It leads to particular difficulty in carrying out two independent motor activities at the same time and can be made worse by emotional stress or concurrent illnesses. Paradoxically people with Parkinson's disease can often ride a bicycle or climb stairs more easily than walk on a level. While most physicians may readily notice bradykinesia, formal assessment requires a person to do repetitive movements with their fingers and feet.<ref>{{cite journal | vauthors = Lees AJ, Hardy J, Revesz T | title = Parkinson's disease | journal = Lancet | volume = 373 | issue = 9680 | pages = 2055–66 | date = June 2009 | pmid = 19524782 | doi = 10.1016/S0140-6736(09)60492-X | s2cid = 42608600 }}</ref>


Beyond the cardinal four, other motor deficits, termed secondary motor symptoms, commonly occur.{{sfn|Moustafa|Chakravarthy|Phillips|Gupta|2016|pp=727-728}} Notably, gait disturbances result in the ], which includes shuffling and ], where a normal gait is interrupted by rapid footsteps—known as festination—or sudden stops, impairing balance and causing falls.{{sfn|Moustafa|Chakravarthy|Phillips|Gupta|2016|p=731}} {{sfn|Mirelman|Bonato|Camicioli|Ellis|2019|p=1}} Most PD patients experience speech problems, including ], ], ], and festinating speech (rapid and poorly intelligible).{{sfn|Moustafa|Chakravarthy|Phillips|Gupta|2016|p=734}} Handwriting is commonly altered in Parkinson's, decreasing in size—known as ]—and becoming jagged and sharply fluctuating.{{sfn|Moustafa|Chakravarthy|Phillips|Gupta|2016|p=732}} Grip and dexterity are also impaired.{{sfn|Moustafa|Chakravarthy|Phillips|Gupta|2016|p=733}}
] is stiffness and resistance to limb movement caused by increased ], an excessive and continuous contraction of muscles.<ref name=Jankovic2008/> In parkinsonism, the rigidity can be uniform, known as "lead-pipe rigidity," or ratchety, known as "cogwheel rigidity."<ref name="pmid15172778"/><ref name=Jankovic2008/><ref name="Banich">{{cite book | vauthors = Banich MT, Compton RJ |chapter=Motor control | title=Cognitive neuroscience|publisher=Wadsworth, Cengage learning|location=Belmont, CA|year=2011 |pages= 108–44|isbn=978-0-8400-3298-0}}</ref><ref>{{cite book|title=Oxford Handbook of Clinical Medicine|page=486 |date=4 January 2007 |publisher=] | vauthors = Longmore M, Wilkinson IB, Turmezei T, Cheung CK |isbn=978-0-19-856837-7}}</ref> The combination of tremor and increased tone is considered to be at the origin of cogwheel rigidity.<ref name="Jankovic_book-Rigidity">{{Cite book | vauthors = Fung VS, Thompson PD | chapter=Rigidity and spasticity | editor1-last=Tolosa | editor1-first=Eduardo | editor2-last=Jankovic | title=Parkinson's disease and movement disorders | publisher=Lippincott Williams & Wilkins | location=Hagerstown, MD | year=2007 | pages= 504–13 | isbn=978-0-7817-7881-7}}</ref> Rigidity may be associated with joint pain; such pain being a frequent initial manifestation of the disease.<ref name=Jankovic2008/> In early stages of Parkinson's disease, rigidity is often asymmetrical and it tends to affect the neck and shoulder muscles prior to the muscles of the face and extremities.<ref>{{cite book | last1=O'Sullivan |first1=Susan B |last2=Schmitz |first2=Thomas J | name-list-style = vanc |title=Physical Rehabilitation |edition=5th |chapter=Parkinson's Disease |year=2007|publisher=F.A. Davis|location=Philadelphia |pages=856–57 }}</ref> With the progression of the disease, rigidity typically affects the whole body and reduces the ability to move.


===Non-motor===
] is typical in the later stages of the disease, leading to impaired balance and frequent falls,<ref name="OFP"/> and secondarily to ]s, loss of confidence, and reduced mobility.<ref>{{cite book| first1 = Mark | last1 = Hallett | first2 = Werner | last2 = Poewe | name-list-style = vanc |title=Therapeutics of Parkinson's Disease and Other Movement Disorders|url=https://books.google.com/books?id=fEezGoZ4h7YC&pg=PA417|date=13 October 2008|publisher=John Wiley & Sons|isbn=978-0-470-71400-3|page=417|url-status=live|archive-url=https://web.archive.org/web/20170908154209/https://books.google.com/books?id=fEezGoZ4h7YC&pg=PA417|archive-date=8 September 2017}}</ref> Instability is often absent in the initial stages, especially in younger people, especially prior to the development of bilateral symptoms.<ref>{{cite journal | vauthors = Hoehn MM, Yahr MD | title = Parkinsonism: onset, progression and mortality | journal = Neurology | volume = 17 | issue = 5 | pages = 427–42 | date = May 1967 | pmid = 6067254 | doi = 10.1212/wnl.17.5.427 | doi-access = free }}</ref> Up to 40% of people diagnosed with PD may experience falls and around 10% may have falls weekly, with the number of falls being related to the severity of PD.<ref name=Jankovic2008/>
====Neuropsychiatric and cognitive====
{| class="wikitable" style="float:right; margin-left:1em; font-size:90%; line-height:1.4em; width:280px;"
|+ Neuropsychiatric symptom prevalence in Parkinson's disease{{sfn|Aarslanda|Krambergera|2015|pp=660, 662}}
! rowspan="2" style="background:#33D2FD;color:black;text-align:center;" |Symptom
|-
! style="background:#33D2FD;color:black;" |Prevalence (%)
|-
! ]
|style="text-align:center;"| 40–50
|-
! ]
|style="text-align:center;"| 40
|-
! ]
|style="text-align:center;"| 20–40
|-
! ]
|style="text-align:center;"| 36–60
|-
! ]
|style="text-align:center;"| 15–30
|-
|}
] symptoms like ], ], ], hallucinations, and ] occur in up to 60% of those with Parkinson's. They often precede motor symptoms and vary with disease progression.{{sfn|Aarslanda|Krambergera|2015|pp=659-660}} Non-motor fluctuations, including ], ], and slowness of thought, are also common.{{sfn|Weintraub|Mamikonyan|2019|p=661}} Some neuropsychiatric symptoms are not directly caused by neurodegeneration but rather by its pharmacological management.{{sfn|Aarslanda|Krambergera|2015|p=660}}


Cognitive impairments rank among the most prevalent and debilitating non-motor symptoms.{{Sfn|Biundo|Weis|Antonini|2016|p=1}} These deficits may emerge in the early stages or before diagnosis,{{Sfn|Biundo|Weis|Antonini|2016|p=1}}{{Sfn|Gonzalez-Latapi|Bayram|Litvan|Marras|2021|p=74}} and their prevalence and severity tend to increase with disease progression. Ranging from ] to severe ], these impairments include ], ], and disruptions in time perception and estimation.{{Sfn|Gonzalez-Latapi|Bayram|Litvan|Marras|2021|p=74}}
Other recognized motor signs and symptoms include gait and posture disturbances such as ] (rapid shuffling steps and a ] when walking with no flexed arm swing). Freezing of gait (brief arrests when the feet seem to get stuck to the floor, especially on turning or changing direction), a slurred monotonous quiet voice, mask-like facial expression, and handwriting that gets smaller and smaller are other common signs.<ref>{{cite book | first1 = Rajesh | last1 = Pahwa | first2 = Kelly E. | last2 = Lyons | name-list-style = vanc | title=Handbook of Parkinson's Disease |edition=Third |url=https://books.google.com/books?id=gX5mAIk5F6UC&pg=PA76 |date=25 March 2003 |publisher=CRC Press |isbn=978-0-203-91216-4 |page=76 |url-status=live |archive-url=https://web.archive.org/web/20170908154209/https://books.google.com/books?id=gX5mAIk5F6UC&pg=PA76 |archive-date=8 September 2017 }}</ref>


===Neuropsychiatric=== ====Autonomic====
]—an autonomic failure—can lead to ] (pictured).]]
Parkinson's disease can cause ] disturbances, which can range from mild to severe. This includes disorders of cognition, mood, behavior, and thought.<ref name=Jankovic2008/>
] failures, known as ], can appear at any stage of Parkinson's.{{sfn|Palma|Kaufmann|2018|pp=372-373}}{{sfn|Pfeiffer|2020|p=1464}} They are among the most debilitating symptoms and greatly reduce quality of life.{{sfn|Palma|Kaufmann|2018|p=373}} Although almost all PD patients suffer cardiovascular autonomic dysfunction, only some are symptomatic.{{sfn|Palma|Kaufmann|2018|p=373}} Chiefly, ]—a sustained ] drop of at least 20 mmHg ] or 10 mmHg ] after standing—occurs in 30–50 percent of cases. This can result in ] or ]: subsequent falls are associated with higher morbidity and mortality.{{sfn|Palma|Kaufmann|2018|p=373}}{{sfn|Palma|Kaufmann|2020|pp=1465-1466}}


Other autonomic failures include ] like chronic constipation, ] and subsequent ], ], and ] (difficulty swallowing): all greatly reduce quality of life.{{sfn|Pfeiffer|2020|p=1467}}{{sfn|Han|Finkelstein|McQuade|Diwakarla|2022|p=2}} Dysphagia, for instance, can prevent pill swallowing and lead to ].{{sfn|Pfeiffer|2020|p=1468}} ], ], and ]—including heat and cold intolerance and excessive sweating—also frequently occur.{{sfn|Pfeiffer|2020|pp=1471-1473}}
Cognitive disturbances can occur in the early stages of the disease and sometimes prior to diagnosis, and increase in prevalence with duration of the disease.<ref name=Jankovic2008/><ref name="pmid18175397">{{cite journal | vauthors = Caballol N, Martí MJ, Tolosa E | title = Cognitive dysfunction and dementia in Parkinson disease | journal = Movement Disorders | volume = 22 Suppl 17 | issue = Suppl 17 | pages = S358–66 | date = September 2007 | pmid = 18175397 | doi = 10.1002/mds.21677 | s2cid = 3229727 }}</ref> The most common cognitive deficit in PD is ], which can include problems with planning, ], abstract thinking, rule acquisition, ], initiating appropriate actions, ], and ].<ref name="pmid18175397"/><ref name="PD timing review">{{cite journal | vauthors = Parker KL, Lamichhane D, Caetano MS, Narayanan NS | title = Executive dysfunction in Parkinson's disease and timing deficits | journal = Frontiers in Integrative Neuroscience | volume = 7 | page = 75 | date = October 2013 | pmid = 24198770 | pmc = 3813949 | doi = 10.3389/fnint.2013.00075 }}</ref> Other cognitive difficulties include ], impaired ] and impaired perception and estimation of time.<ref name="pmid18175397"/><ref name="PD timing review" /> Nevertheless, improvement appears when recall is aided by cues.<ref name="pmid18175397"/> Visuospatial difficulties are also part of the disease, seen for example when the individual is asked to perform tests of facial recognition and perception of the orientation of drawn lines.<ref name="pmid18175397"/><ref name="PD timing review" />


====Other non-motor symptoms====
A person with PD has two to six times the risk of dementia compared to the general population.<ref name=Jankovic2008/><ref name="pmid18175397"/> Up to 78% of people with PD have Parkinson's disease dementia.<ref name=Gomperts2016>{{cite journal |vauthors=Gomperts SN |title=Lewy Body Dementias: Dementia With Lewy Bodies and Parkinson Disease Dementia |journal=Continuum (Minneap Minn) |volume=22 |issue=2 Dementia |pages=435–63 |date=April 2016 |pmid=27042903 |pmc=5390937 |doi=10.1212/CON.0000000000000309|type=Review}}</ref> The prevalence of dementia increases with age and, to a lesser degree, duration of the disease.<ref>{{cite journal | vauthors = Garcia-Ptacek S, Kramberger MG | title = Parkinson Disease and Dementia | journal = Journal of Geriatric Psychiatry and Neurology | volume = 29 | issue = 5 | pages = 261–70 | date = September 2016 | pmid = 27502301 | doi = 10.1177/0891988716654985 | s2cid = 21279235 }}</ref> Dementia is associated with a reduced ] in people with PD and their ]s, increased mortality, and a higher probability of needing ].<ref name="pmid18175397"/>
Sensory deficits appear in up to 90 percent of patients and are usually present at early stages.{{Sfn|Zhu|Li|Ye|Jiang|2016|p=685}} ] and ] are common,{{Sfn|Zhu|Li|Ye|Jiang|2016|p=685}} with ] affecting up to 55 percent of individuals.{{Sfn|Corrà|Vila-Chã|Sardoeira|Hansen|2023|pp=225-226}} ] are also frequently observed, including deficits in ], ], ], and ].{{Sfn|Zhu|Li|Ye|Jiang|2016|p=688}} An ] is also prevalent.{{Sfn|Zhu|Li|Ye|Jiang|2016|p=687}} PD patients often struggle with spatial awareness, recognizing faces and emotions, and may experience challenges with reading and double vision.{{Sfn|Weil|Schrag|Warren|Crutch|2016|pp=2828, 2831-2832}}


]s are highly prevalent in PD, affecting up to 98%.{{Sfn|Stefani|Högl|2020|p=121}} These disorders include ], ], ], ] (RBD), and ], many of which can be worsened by medication. RBD may begin years before the initial motor symptoms. Individual presentation of symptoms varies, although most people affected by PD show an altered ] at some point of disease progression.{{sfn|Dodet|Houot|Leu-Semenescu|Corvol|2024|p=1}}{{sfn|Bollu|Sahota|2017|pp=381-382}}
Impulse control disorders including pathological gambling, compulsive sexual behavior, binge eating, compulsive shopping and reckless generosity can be caused by medication, particularly orally active dopamine agonists. The ] – with wanting of medication leading to overusage – is a rare complication of levodopa use.<ref name="Noyce"/>


PD is also associated with a variety of ]s that include ], ], ], and ].{{sfn|Niemann|Billnitzer|Jankovic|2021|p=61}} Seborrheic dermatitis is recognized as a premotor feature that indicates dysautonomia and demonstrates that PD can be detected not only by changes of ], but tissue abnormalities outside the nervous system as well.{{sfn|Almikhlafi|2024|p=7}}
] in which complicated repetitive aimless ] occur for many hours is another disturbance caused by anti-Parkinson medication.

===Psychosis===
] can be considered a symptom with a prevalence at its widest range from 26-83%.<ref name=":5" /><ref>{{Cite journal|last=Ffytche|first=Dominic H.|last2=Creese|first2=Byron|last3=Politis|first3=Marios|last4=Chaudhuri|first4=K. Ray|last5=Weintraub|first5=Daniel|last6=Ballard|first6=Clive|last7=Aarsland|first7=Dag|date=2017-02-01|title=The psychosis spectrum in Parkinson disease|journal=Nature Reviews. Neurology|volume=13|issue=2|pages=81–95|doi=10.1038/nrneurol.2016.200|issn=1759-4766|pmc=5656278|pmid=28106066}}</ref> ]s or ]s occur in approximately 50% of people with PD over the course of the illness, and may herald the emergence of dementia. These range from minor hallucinations – "sense of passage" (something quickly passing beside the person) or "sense of presence" (the perception of something/someone standing just to the side or behind the person) – to full blown vivid, ] and ] ideation. Auditory hallucinations are uncommon in PD, and are rarely described as voices. It is now believed that psychosis is an integral part of the disease. A psychosis with delusions and associated ] is a recognized complication of anti-Parkinson drug treatment and may also be caused by urinary tract infections (as frequently occurs in the fragile elderly), but drugs and infection are not the only factors, and underlying brain pathology or changes in neurotransmitters or their receptors (e.g., acetylcholine, serotonin) are also thought to play a role in psychosis in PD.<ref>{{cite journal | vauthors = Shergill SS, Walker Z, Le Katona C | title = A preliminary investigation of laterality in Parkinson's disease and susceptibility to psychosis | journal = Journal of Neurology, Neurosurgery, and Psychiatry | volume = 65 | issue = 4 | pages = 610–11 | date = October 1998 | pmid = 9771806 | pmc = 2170290 | doi = 10.1136/jnnp.65.4.610 }}</ref><ref name="pmid20538500">{{cite journal | vauthors = Friedman JH | title = Parkinson's disease psychosis 2010: a review article | journal = Parkinsonism & Related Disorders | volume = 16 | issue = 9 | pages = 553–60 | date = November 2010 | pmid = 20538500 | doi = 10.1016/j.parkreldis.2010.05.004 }}</ref>

=== Behavior and mood ===
Behavior and mood alterations are more common in PD without cognitive impairment than in the general population, and are usually present in PD with dementia. The most frequent mood difficulties are ], ], and ].<ref name="Jankovic2008" />

] has been estimated to appear in anywhere from 20-35% of people with PD, and can appear at any stage of the disease. In Parkinson's, depression can manifest with symptoms that are common to the disease process (fatigue, insomnia, and difficulty with concentration) which makes diagnosis difficult. The imbalance and change in ], ], and ] hormones are known to be a primary cause of depression in PD affected people.<ref name=":5">{{Cite journal|last=Han|first=Ji Won|last2=Ahn|first2=Yebin D.|last3=Kim|first3=Won-Seok|last4=Shin|first4=Cheol Min|last5=Jeong|first5=Seong Jin|last6=Song|first6=Yoo Sung|last7=Bae|first7=Yun Jung|last8=Kim|first8=Jong-Min|date=2018-11-19|title=Psychiatric Manifestation in Patients with Parkinson's Disease|url=https://pubmed.ncbi.nlm.nih.gov/30450025|journal=Journal of Korean Medical Science|volume=33|issue=47|pages=e300|doi=10.3346/jkms.2018.33.e300|issn=1598-6357|pmc=6236081|pmid=30450025}}</ref> Another cause is the functional impairment that is caused by the disease.<ref name=":6">{{Cite journal|last=Weintraub|first=Daniel|last2=Mamikonyan|first2=Eugenia|date=September 2019|title=The Neuropsychiatry of Parkinson Disease: A Perfect Storm|url=https://pubmed.ncbi.nlm.nih.gov/31006550|journal=The American Journal of Geriatric Psychiatry: Official Journal of the American Association for Geriatric Psychiatry|volume=27|issue=9|pages=998–1018|doi=10.1016/j.jagp.2019.03.002|issn=1545-7214|pmc=7015280|pmid=31006550}}</ref> Symptoms of depression can include loss of interest, sadness, guilt, feelings of helplessness/hopelessness/guilt, and suicidal ideation. ] in PD affected people is higher than in the general population, but suicidal attempts themselves are lower than in people with depression without PD.<ref name=":5" /><ref name=":6" /> Risk factors for depression in PD can include disease onset under age 50, being a woman, previous history of depression, severe motor symptoms, and others.<ref name=":5" />

] has been estimated to have a prevalence in PD affected people around 30%-40% (however up to 60% has been found).<ref name=":5" /><ref name=":6" /> Anxiety can often be found during "off" periods (periods of time where medication is not working as well as it did before) with PD affected people suffering from panic attacks more frequently compared to the general population. Both anxiety and depression have been found to be associated with decreased quality of life.<ref name=":5" /><ref name=":7">{{Cite journal|last=Goetz|first=Christopher G.|date=2010|title=New developments in depression, anxiety, compulsiveness, and hallucinations in Parkinson's disease: Behavioral Aspects of PD|url=http://doi.wiley.com/10.1002/mds.22636|journal=Movement Disorders|language=en|volume=25|issue=S1|pages=S104–S109|doi=10.1002/mds.22636}}</ref> Symptoms can range from mild and episodic to chronic with potential causes being abnormal ] levels as well as embarrassment or fear about their symptoms/disease.<ref name=":5" /><ref name=":7" /> Risk factors for anxiety in PD are disease onset under age 50, women, and "off" periods.<ref name=":5" />

] and ] can be defined as a loss of motivation and an impaired ability to experience pleasure, respectively. They are symptoms classically associated with depression however differ in PD affected people in treatment, mechanism, and doesn't always occur with depression. Apathy presents in around 16.5-40%. Symptoms of apathy include reduced initiative/interests in new activities or the world around them, emotional indifference, and loss of affection or concern for others.<ref name=":5" /> Apathy is associated with deficits in cognitive functions including executive and verbal memory.<ref name=":6" />

===Other===

]s are a feature of the disease and can be worsened by medications.<ref name=Jankovic2008/> Symptoms can manifest as daytime ] (including sudden sleep attacks resembling ]), disturbances in ] sleep, or ].<ref name=Jankovic2008/> ] (RBD), in which people act out dreams, sometimes injuring themselves or their bed partner, may begin many years before the development of motor or cognitive features of PD or ].<ref>{{cite journal | vauthors = Kim YE, Jeon BS | title = Clinical implication of REM sleep behavior disorder in Parkinson's disease | journal = Journal of Parkinson's Disease | volume = 4 | issue = 2 | pages = 237–44 | date = 1 January 2014 | pmid = 24613864 | doi = 10.3233/jpd-130293 }}</ref>

Alterations in the ] can lead to ] (low blood pressure upon standing), ] and excessive sweating, ], and altered sexual function.<ref name=Jankovic2008/> ] and ] can be severe enough to cause discomfort and even endanger health.<ref name="pmid19691125"/> Changes in perception may include an impaired sense of smell, disturbed vision, pain, and ] (tingling and numbness).<ref name=Jankovic2008/> All of these symptoms can occur years before diagnosis of the disease.<ref name=Jankovic2008/>


==Causes== ==Causes==
{{Main|Causes of Parkinson's disease}} {{Main|Causes of Parkinson's disease}}
{{multiple image
| align = right
| total_width = 320
| image1 = Alpha-synuclein 2005.png
| alt1 =
| caption1 =
| image2 = Lewy bodies (alpha synuclein inclusions) 1.jpg
| alt2 =
| footer = The protein ] aggregates into ]. Structural model of alpha-synuclein (left), photomicrograph of Lewy bodies (right).
}}
As of 2024, the cause of neurodegeneration in Parkinson's remains unclear,{{sfn|Morris|Spillantini|Sue|Williams-Gray|2024}} though it is believed to result from the interplay of ] and ] factors.{{sfn|Morris|Spillantini|Sue|Williams-Gray|2024}} The majority of cases are ] with no clearly identifiable cause, while approximately 5–10 percent are familial.{{sfn|Toffoli|Vieira|Schapira|2020|p=1}} Around a third of familial cases can be attributed to a single monogenic cause.{{sfn|Toffoli|Vieira|Schapira|2020|p=1}}


Molecularly, abnormal aggregation of alpha-synuclein is considered a key contributor to PD ],{{sfn|Morris|Spillantini|Sue|Williams-Gray|2024}} although the trigger for this aggregation remains debated.{{sfn|Brundin|Melki|2017|p=9808}} ] disruption and the dysfunction of cell ], including ], ], and ], are implicated in pathogenesis.{{sfn|Morris|Spillantini|Sue|Williams-Gray|2024}}{{sfn|Ho|Wing|2024|pp=1-2}} Additionally, maladaptive immune and inflammatory responses are potential contributors.{{sfn|Morris|Spillantini|Sue|Williams-Gray|2024}} The substantial heterogeneity in PD presentation and progression suggests the involvement of multiple interacting triggers and pathogenic pathways.{{sfn|Brundin|Melki|2017|p=9808}}
Many risk factors have been proposed, sometimes in relation to theories concerning possible mechanisms of the disease; however, none have been conclusively proven.<ref name="pmid16713924"/> The most frequently replicated relationships are an increased risk in those exposed to pesticides, and a reduced risk in smokers.<ref name="pmid16713924"/><ref name=Barreto2015>{{cite journal | vauthors = Barreto GE, Iarkov A, Moran VE | title = Beneficial effects of nicotine, cotinine and its metabolites as potential agents for Parkinson's disease | journal = Frontiers in Aging Neuroscience | volume = 6 | page = 340 | date = January 2015 | pmid = 25620929 | pmc = 4288130 | doi = 10.3389/fnagi.2014.00340 }}</ref> There is a possible link between PD and '']'' infection that can prevent the absorption of some drugs including levodopa.<ref>{{cite journal | vauthors = Çamcı G, Oğuz S | title = Association between Parkinson's Disease and ''Helicobacter Pylori'' | journal = Journal of Clinical Neurology | volume = 12 | issue = 2 | pages = 147–50 | date = April 2016 | pmid = 26932258 | pmc = 4828559 | doi = 10.3988/jcn.2016.12.2.147 }}</ref><ref>{{cite journal | vauthors = McGee DJ, Lu XH, Disbrow EA | title = Stomaching the Possibility of a Pathogenic Role for Helicobacter pylori in Parkinson's Disease | journal = Journal of Parkinson's Disease | volume = 8 | issue = 3 | pages = 367–74 | year = 2018 | pmid = 29966206 | pmc = 6130334 | doi = 10.3233/JPD-181327 }}</ref>


=== Genetic ===
===Environmental factors and exposures===
] of ]]]
Exposure to ] and a history of head injury have each been linked with Parkinson disease (PD), but the risks are modest. Never having smoked cigarettes, and never drinking caffeinated beverages, are also associated with small increases in risk of developing PD.<ref name="Noyce">{{cite journal | vauthors = Noyce AJ, Bestwick JP, Silveira-Moriyama L, ''et al'' | title = Meta-analysis of early nonmotor features and risk factors for Parkinson disease | journal = Annals of Neurology | volume = 72 | issue = 6 | pages = 893–901 | date = December 2012 | pmid = 23071076 | pmc = 3556649 | doi = 10.1002/ana.23687 |type= Review}}</ref>
Parkinson's can be narrowly defined as a genetic disease, as rare inherited gene variants have been firmly linked to monogenic PD, and the majority of sporadic cases carry variants that increase PD risk.{{sfn|Morris|Spillantini|Sue|Williams-Gray|2024}}{{sfn|Toffoli|Vieira|Schapira|2020|p=2}}{{sfn|Salles|Tirapegui|Chaná-Cuevas|2024|p=2}} PD ] is estimated to range from 22 to 40 percent.{{sfn|Morris|Spillantini|Sue|Williams-Gray|2024}} Around 15 percent of diagnosed individuals have a ], of which 5–10 percent can be attributed to a causative risk gene ]. However, carrying one of these mutations may not lead to disease. Rates of familial PD vary by ethnicity: monogenic PD occurs in up to 40% of ] patients and 20% of ] patients.{{sfn|Salles|Tirapegui|Chaná-Cuevas|2024|p=2}}


As of 2024, around 90 genetic risk variants across 78 genomic loci have been identified.{{sfn|Farrow|Gokuladhas|Schierding|Pudjihartono|2024|p=1}} Notable risk variants include ''SNCA'' (which encodes alpha-synuclein), ''LRRK2'', and ''VPS35'' for ] inheritance, and ''PRKN'', ''PINK1'', and ''DJ1'' for ] inheritance.{{sfn|Morris|Spillantini|Sue|Williams-Gray|2024}}{{sfn|Bandres-Ciga|Diez-Fairen|Kim|Singleton|2020|p=2}} ''LRRK2'' is the most common autosomal dominant variant, responsible for 1–2 percent of all PD cases and 40 percent of familial cases.{{sfn|Tanner|Ostrem|2024}} {{sfn|Toffoli|Vieira|Schapira|2020|p=1}} ] variants are associated with nearly half of recessive, early-onset monogenic PD.{{sfn|Toffoli|Vieira|Schapira|2020|pp=1-2}} Mutations in the ''GBA1'' gene, linked to ], are found in 5–15 percent of PD cases.{{sfn|Smith|Schapira|2022|pp=1-15}} The ''GBA1'' variant frequently leads to cognitive decline.{{sfn|Tanner|Ostrem|2024}}
Low concentrations of ] in the blood ] is associated with an increased risk of PD.<ref>{{cite journal | vauthors = Chahine LM, Stern MB, Chen-Plotkin A | title = Blood-based biomarkers for Parkinson's disease | journal = Parkinsonism & Related Disorders | volume = 20 Suppl 1 | pages = S99–103 | date = January 2014 | pmid = 24262199 | pmc = 4070332 | doi = 10.1016/S1353-8020(13)70025-7 }}</ref>


===Environmental===
====Drug-Induced Parkinsonism====
{{See also|Environmental health|Exposome}}
Different medical drugs have been indicated in cases of parkinsonism. Drug-induced parkinsonism is normally reversible by stopping the offending agent.<ref name=":0">{{Cite book|last=Simon|first=Roger|title=Clinical Neurology|last2=Aminoff|last3=Greenberg|publisher=McGraw-Hill|year=2017|isbn=978-1-259-86172-7|edition=10|location=The United States of America|pages=}}</ref> Drugs include but not are not limited to:
]
The limited heritability of Parkinson's strongly suggests environmental factors are involved, though identifying these risk factors and establishing ] is challenging due to PD's decade-long prodromal period.{{sfn|De Mirandaa|Goldmanb|Millerc|Greenamyred|2024|p=46}} However, environmental toxicants such as air pollution, pesticides, and industrial solvents like ] are strongly linked to Parkinson's.{{sfn|Dorsey|Bloem|2024|pp=453-454}}


Certain pesticides—like ], ], and ]—are the most established environmental toxicants for Parkinson's and are likely causal.{{sfn|Dorsey|Bloem|2024|p=454}}{{sfn|Bloem|Boonstra|2023|p=e948–e949}}{{sfn|Rietdijk|Perez-Pardo|Garssen|van Wezel|2017|p=1}} PD prevalence is strongly associated with local pesticide use, and many pesticides are mitochondrial toxins.{{sfn|Dorsey|Bloem|2024|pp=453-455}} Paraquat, for instance, structurally resembles metabolized ],{{sfn|Dorsey|Bloem|2024|p=454}} which selectively kills dopaminergic neurons by inhibiting ] and is widely used to ] PD.{{sfn|Langston|2017|p=S14}}{{sfn|Dorsey|Bloem|2024|p=454}} Pesticide exposure after diagnosis may also accelerate disease progression.{{sfn|Dorsey|Bloem|2024|p=454}} Without pesticide exposure, an estimated 20 percent of all PD cases would be prevented.{{sfn|Santos-Lobato|2024|p=1}}
* ]s (chlorpromazine, promazine, etc.)
* ]s (haloperidol, benperidol, etc.)
* ]
* ]


===Hypotheses===
] (MPTP) is a drug known for causing irreversible parkinsonism that is commonly used in animal model research.<ref name=":0" /><ref>{{Cite journal|last=Langston|first=J. William|date=2017-03-06|title=The MPTP Story|url=https://www.medra.org/servlet/aliasResolver?alias=iospress&doi=10.3233/JPD-179006|journal=Journal of Parkinson's Disease|volume=7|issue=s1|pages=S11–S19|doi=10.3233/JPD-179006|pmc=5345642|pmid=28282815}}</ref><ref>{{Cite journal|last=Song|first=Liang|last2=Xu|first2=Meng-Bei|last3=Zhou|first3=Xiao-Li|last4=Zhang|first4=Dao-pei|last5=Zhang|first5=Shu-ling|last6=Zheng|first6=Guo-qing|date=2017|title=A Preclinical Systematic Review of Ginsenoside-Rg1 in Experimental Parkinson’s Disease|url=https://www.hindawi.com/journals/omcl/2017/2163053/|journal=Oxidative Medicine and Cellular Longevity|language=en|volume=2017|pages=1–14|doi=10.1155/2017/2163053|issn=1942-0900|pmc=5366755|pmid=28386306}}</ref>
====Prionic hypothesis====
{{See also|Prion}}
The hallmark of Parkinson's is the formation of protein aggregates, beginning with alpha-synuclein fibrils and followed by Lewy bodies and Lewy neurites.{{sfn|Wu|Schekman|2024|p=1}} The prion hypothesis suggests that alpha-synuclein aggregates are pathogenic and can spread to neighboring, healthy neurons and seed new aggregates. Some propose that the heterogeneity of PD may stem from different "strains" of alpha-synuclein aggregates and varying anatomical sites of origin.{{sfn|Brundin|Melki|2017|p=9809}}{{sfn|Vázquez-Vélez|Zoghbi|2021|p=96}} Alpha-synuclein propagation has been demonstrated in cell and animal models and is the most popular explanation for the progressive spread through specific neuronal systems.{{sfn|Dickson|2018|p=S31}} However, therapeutic efforts to clear alpha-synuclein have failed.{{sfn|Wu|Schekman|2024|pp=1-2}} Additionally, postmortem brain tissue analysis shows that alpha-synuclein pathology does not clearly progress through the nearest neural connections.{{sfn|Brundin|Melki|2017|p=9812}}


==== Toxin-Induced Parkinsonism ==== ====Braak's hypothesis====
{{Main|Parkinson's disease and gut-brain axis#Braak's hypothesis}}
Some toxins can cause parkinsonism. These toxins include but are not limited to ] and ] <ref>{{Cite journal|last=Guilarte|first=Tomás R.|last2=Gonzales|first2=Kalynda K.|date=August 2015|title=Manganese-Induced Parkinsonism Is Not Idiopathic Parkinson's Disease: Environmental and Genetic Evidence|url=https://pubmed.ncbi.nlm.nih.gov/26220508|journal=Toxicological Sciences: An Official Journal of the Society of Toxicology|volume=146|issue=2|pages=204–212|doi=10.1093/toxsci/kfv099|issn=1096-0929|pmc=4607750|pmid=26220508}}</ref><ref name=":0" /><ref>{{Cite journal|last=Kwakye|first=Gunnar|last2=Paoliello|first2=Monica|last3=Mukhopadhyay|first3=Somshuvra|last4=Bowman|first4=Aaron|last5=Aschner|first5=Michael|date=2015-07-06|title=Manganese-Induced Parkinsonism and Parkinson’s Disease: Shared and Distinguishable Features|url=http://www.mdpi.com/1660-4601/12/7/7519|journal=International Journal of Environmental Research and Public Health|language=en|volume=12|issue=7|pages=7519–7540|doi=10.3390/ijerph120707519|issn=1660-4601|pmc=4515672|pmid=26154659}}</ref><ref>{{Cite journal|last=Kim|first=Eun-A|last2=Kang|first2=Seong-Kyu|date=2010|title=Occupational Neurological Disorders in Korea|url=https://jkms.org/DOIx.php?id=10.3346/jkms.2010.25.S.S26|journal=Journal of Korean Medical Science|language=en|volume=25|issue=Suppl|pages=S26|doi=10.3346/jkms.2010.25.S.S26|issn=1011-8934|pmc=3023358|pmid=21258587}}</ref>
In 2002, ] and colleagues proposed that Parkinson's disease begins outside the brain and is triggered by a "neuroinvasion" of some unknown pathogen.{{sfn|Dorsey|De Mirandab|Horsager|Borghammer|2024|p=363}}{{sfn|Rietdijk|Perez-Pardo|Garssen|van Wezel|2017|p=2}} The pathogen enters through the nasal cavity and is swallowed into the digestive tract, initiating Lewy pathology in both areas.{{sfn|Rietdijk|Perez-Pardo|Garssen|van Wezel|2017|p=1}}{{sfn|Dorsey|De Mirandab|Horsager|Borghammer|2024|p=363}} This alpha-synuclein pathology may then travel from the gut to the central nervous system through the ].{{sfn|Rietdijk|Perez-Pardo|Garssen|van Wezel|2017|p=3}} This theory could explain the presence of Lewy pathology in both the enteric nervous system and olfactory tract neurons, as well as clinical symptoms like loss of small and gastrointestinal problems.{{sfn|Rietdijk|Perez-Pardo|Garssen|van Wezel|2017|p=2}} It has also been suggested that environmental toxicants might be ingested in a similar manner to trigger PD.{{sfn|Dorsey|De Mirandab|Horsager|Borghammer|2024|pp=363-364, 371-372}}


====Catecholaldehyde hypothesis====
===Genetics===
{{Main|Catecholaldehyde hypothesis}}
]
] argues that the ] metabolite ] (pictured) triggers ] aggregation.]]
Research indicates that PD is the product of a complex interaction of genetic and ]s.<ref name=Lancet2015/> Around 15% of individuals with PD have a ] who has the disease,<ref name="pmid15172778"/> and 5–10% of people with PD are known to have forms of the disease that occur because of a ] in one of several specific genes.<ref name=lesage>{{cite journal | vauthors = Lesage S, Brice A | title = Parkinson's disease: from monogenic forms to genetic susceptibility factors | journal = Human Molecular Genetics | volume = 18 | issue = R1 | pages = R48–59 | date = April 2009 | pmid = 19297401 | doi = 10.1093/hmg/ddp012 | doi-access = free }}</ref><ref name=":8">{{Cite journal|last=Deng|first=Hao|last2=Wang|first2=Peng|last3=Jankovic|first3=Joseph|date=March 2018|title=The genetics of Parkinson disease|url=https://pubmed.ncbi.nlm.nih.gov/29288112|journal=Ageing Research Reviews|volume=42|pages=72–85|doi=10.1016/j.arr.2017.12.007|issn=1872-9649|pmid=29288112}}</ref> Harboring one of these gene mutations may not lead to the disease; susceptibility factors put the individual at an increased risk, often in combination with other risk factors, which also affect age of onset, severity and progression.<ref name=lesage/> At least 11 ] and 9 ] ]s have been implicated in the development of PD. The autosomal dominant genes include ], ], ], ], ], ], ], TMEM230, ], ], ]. Autosomal recessive genes include ], ], ], ], ], ], ], SYNJ1, and VPS13C. Some genes are ] or have unknown inheritance pattern: those include PARK10, PARK12, and PARK16. ] deletion is also known to be associated with PD.<ref>{{Cite journal|last=Puschmann|first=Andreas|date=September 2017|title=New Genes Causing Hereditary Parkinson's Disease or Parkinsonism|url=https://pubmed.ncbi.nlm.nih.gov/28733970|journal=Current Neurology and Neuroscience Reports|volume=17|issue=9|pages=66|doi=10.1007/s11910-017-0780-8|issn=1534-6293|pmc=5522513|pmid=28733970}}</ref><ref name=":8" /> An ] form has been associated with mutations in the ] gene.<ref name="Quadri2018">{{cite journal|vauthors=Quadri M, Mandemakers W, Grochowska MM, ''et al''|date=July 2018|title=LRP10 genetic variants in familial Parkinson's disease and dementia with Lewy bodies: a genome-wide linkage and sequencing study|journal=The Lancet. Neurology|volume=17|issue=7|pages=597–608|doi=10.1016/s1474-4422(18)30179-0|pmid=29887161|doi-access=free|s2cid=47009438}}</ref><ref>{{Cite journal|last=Chen|first=You|last2=Cen|first2=Zhidong|last3=Zheng|first3=Xiaosheng|last4=Pan|first4=Qinqing|last5=Chen|first5=Xinhui|last6=Zhu|first6=Lili|last7=Chen|first7=Si|last8=Wu|first8=Hongwei|last9=Xie|first9=Fei|last10=Wang|first10=Haotian|last11=Yang|first11=Dehao|date=June 2019|title=LRP10 in autosomal-dominant Parkinson's disease|url=https://pubmed.ncbi.nlm.nih.gov/30964957|journal=Movement Disorders: Official Journal of the Movement Disorder Society|volume=34|issue=6|pages=912–916|doi=10.1002/mds.27693|issn=1531-8257|pmid=30964957}}</ref>
The enzyme ] (MAO) plays a central role in the metabolism of the neurotransmitter ] and other ]. The ] argues that the oxidation of dopamine by MAO into ] (DOPAL) and ] and the subsequent abnormal accumulation thereof leads to neurodegeneration. The theory posits that DOPAL interacts with alpha-synuclein and causes it to aggregate.{{sfn|Goldstein|2020|p=169}}{{sfn|Goldstein|2021|pp=1-3}}


====Mitochondrial dysfunction====
About 5% of people with PD have mutations in the '']'' gene.<ref name=Stoker2018>{{cite book | vauthors = Stoker TB, Torsney KM, Barker RA | date = 2018 | chapter = Pathological mechanisms and clinical aspects of GBA1 mutation-associated Parkinson’s disease. | veditors = Stoker TB, Greenland JC | title = Parkinson's Disease: Pathogenesis and clinical aspects. | location = Brisbane | publisher = Codon Publications }}</ref> These mutations are present in less than 1% of the unaffected population. The risk of developing PD is increased 20–30 fold if these mutations are present. PD associated with these mutations has the same clinical features, but an earlier age of onset and a more rapid cognitive and motor decline. This gene encodes ]. Low levels of this enzyme cause ].
Whether mitochondrial dysfunction is a cause or consequence of PD pathology remains unclear.{{sfn|Chen|Turnbull|Reeve|2019|pp=1, 15}} Impaired ], increased ], and reduced ] may contribute to neurodegeneration.{{sfn|Chen|Turnbull|Reeve|2019|pp=1, 4-5, 15}} The finding that ]—a ] inhibitor and MPTP metabolite—caused parkinsonian symptoms strongly implied that mitochondria contributed to PD pathogenesis.{{sfn|Chen|Turnbull|Reeve|2019|p=2}}{{sfn|Borsche|Pereira|Klein|Grünewald|2021|p=45}} Alpha-synuclein and toxicants like ] similarly disrupt respiratory complex I.{{sfn|Chen|Turnbull|Reeve|2019|p=2, 13}} Additionally, faulty gene variants involved in familial Parkinson's—including ''PINK1'' and ''Parkin''—prevent the elimination of dysfunctional mitochondria through ].{{sfn|Chen|Turnbull|Reeve|2019|pp=6-7, 8, 15}}{{sfn|Borsche|Pereira|Klein|Grünewald|2021|pp=47-49}}


====Neuroinflammation====
''SNCA'' gene mutations are important in PD because the protein which this gene encodes, ], is the main component of the ] that accumulate in the brains of people with PD.<ref name=lesage/> ] activates ATM (]), a major ] repair signaling ].<ref name = Abugable2019>{{cite journal | vauthors = Abugable AA, Morris JL, Palminha NM, ''et al'' | title = DNA repair and neurological disease: From molecular understanding to the development of diagnostics and model organisms | journal = DNA Repair | volume = 81 | page = 102669 | date = September 2019 | pmid = 31331820 | doi = 10.1016/j.dnarep.2019.102669 | doi-access = free }}</ref> In addition, alpha-synuclein activates the ] ] pathway. The aggregation of alpha-synuclein in ] appears to be a link between reduced ] and brain cell death in PD.<ref name = Abugable2019/>
Some hypothesize that neurodegeneration arises from a chronic ] created by local activated ] and infiltrating immune cells.{{sfn|Morris|Spillantini|Sue|Williams-Gray|2024}} Mitochondrial dysfunction may also drive immune activation, particularly in monogenic PD.{{sfn|Morris|Spillantini|Sue|Williams-Gray|2024}} Some ] increase the risk of developing PD, supporting an autoimmune contribution.{{sfn|Tan|Chao|West|Chan|2020|p=303}} Additionally, ] and ] infections increase the risk of PD, possibly due to a ] alpha-synuclein.{{sfn|Tan|Chao|West|Chan|2020|p=304}} Parkinson's risk is also decreased with ].{{sfn|Morris|Spillantini|Sue|Williams-Gray|2024}}


== Pathophysiology ==
Mutations in some genes, including ''SNCA'', ''LRRK2'' and ''GBA'', have been found to be risk factors for "sporadic" (non-familial) PD.<ref name=lesage/> Mutations in the gene ''LRRK2'' are the most common known cause of familial and sporadic PD, accounting for approximately 5% of individuals with a family history of the disease and 3% of sporadic cases.<ref name="pmid18398010">{{cite journal | vauthors = Davie CA | title = A review of Parkinson's disease | journal = British Medical Bulletin | volume = 86 | issue = 1 | pages = 109–27 | year = 2008 | pmid = 18398010 | doi = 10.1093/bmb/ldn013 | doi-access = free }}</ref><ref name=lesage/> A mutation in ''GBA'' presents the greatest genetic risk of developing Parkinsons disease.<ref name="pmid25904081">{{cite journal|vauthors=Kalia LV, Lang AE|date=August 2015|title=Parkinson's disease|journal=Lancet|volume=386|issue=9996|pages=896–912|doi=10.1016/S0140-6736(14)61393-3|pmid=25904081|s2cid=5502904}}</ref>
{{Main|Pathophysiology of Parkinson's disease}}
]-releasing ]s in the ], seen by the loss of dark ] in the lower inset.]]
Parkinson's disease has two hallmark pathophysiological processes: the abnormal aggregation of alpha-synuclein that leads to Lewy pathology, and the degeneration of dopaminergic neurons in the ].{{sfn|Pardo-Moreno|García-Morales|Suleiman-Martos|Rivas-Domínguez|2023|p=3}}{{sfn|Vázquez-Vélez|Zoghbi|2021|p=88}} The death of these neurons reduces available dopamine in the ], which in turn affects circuits controlling movement in the ].{{sfn|Vázquez-Vélez|Zoghbi|2021|p=88}} By the time motor symptoms appear, 50–80 percent of all dopaminergic neurons in the substantia nigra have degenerated.{{sfn|Vázquez-Vélez|Zoghbi|2021|p=88}}


However, cell death and Lewy pathology are not limited to the substantia nigra.{{sfn|Dickson|2018|p=S32}} The ] holds that alpha-synuclein pathology begins in the ] or outside the central nervous system in the ] before ascending the brain stem.{{sfn|Ye|Robak|Yu|Cykowski|2023|p=98}} In the third Braak stage, Lewy body pathology appears in the substantia nigra,{{sfn|Ye|Robak|Yu|Cykowski|2023|p=98}} and, by the sixth step, Lewy pathology has spread to the limbic and neocortical regions.{{sfn|Vázquez-Vélez|Zoghbi|2021|p=93}} Although Braak staging offers a strong basis for PD progression, the Lewy pathology around 50 percent patients do not adhere to the predicted model.{{sfn|Henderson|Trojanowski|Lee|2019|p=2}} Indeed, Lewy pathology is highly variable and may be entirely absent in some PD patients.{{sfn|Dickson|2018|p=S32}}{{sfn|Ye|Robak|Yu|Cykowski|2023|p=96}}
Several Parkinson-related genes are involved in the function of ]s, organelles that digest cellular waste products. It has been suggested that some cases of PD may be caused by ] that reduce the ability of cells to break down ].<ref>{{cite journal | vauthors = Gan-Or Z, Dion PA, Rouleau GA | title = Genetic perspective on the role of the autophagy-lysosome pathway in Parkinson disease | journal = Autophagy | volume = 11 | issue = 9 | pages = 1443–57 | date = 2 September 2015 | pmid = 26207393 | pmc = 4590678 | doi = 10.1080/15548627.2015.1067364 }}</ref>


===Alpha-synuclein pathology===
*
{{Further|Protein aggregation|Lewy body}}
] stained brown in PD brain tissue]]
Alpha-synuclein is an intracellular protein typically localized to ] and involved in ], ], and ].{{sfn|Henderson|Trojanowski|Lee|2019|p=2}}{{sfn|Chen|Gu|Wang|2022}} When ], it can aggregate into oligomers and proto-fibrils that in turn lead to Lewy body formation.{{sfn|Chen|Gu|Wang|2022}}{{sfn|Menšíková|Matěj|Colosimo|Rosales|2022|p=8}}{{sfn|Borghammer|2018|p=5}} Due to their lower ], oligomers and proto-fibrils may disseminate and be transmitted to other cells more rapidly.{{sfn|Borghammer|2018|p=5}}


Lewy bodies consist of a fibrillar exterior and granular core. Although alpha-synuclein is the dominant ] component, the core contains mitochondrial and autophagosomal membrane components, suggesting a link with organelle dysfunction.{{sfn|Vázquez-Vélez|Zoghbi|2021|p=95}}{{sfn|Vázquez-Vélez|Zoghbi|2021|p=89}} It is unclear whether Lewy bodies themselves contribute to or are simply the result of PD pathogenesis: alpha-synuclein oligomers can independently mediate cell damage, and neurodegeneration can precede Lewy body formation.{{sfn|Menšíková|Matěj|Colosimo|Rosales|2022|p=6}}
=== Vascular Parkinsonism ===
Vascular parkinsonism is the phenomena of the presence of Parkinson's disease symptoms combined with findings of vascular events (such as a ]). The damaging of the ] are similar causes of both vascular parkinsonism and idiopathic Parkinson's Disease, so they can present with many of the same symptoms. Differentiation can be made with careful bedside examination, history taking, and imaging.<ref>{{Cite journal|last=Gupta|first=Deepak|last2=Kuruvilla|first2=Abraham|date=2011-12-01|title=Vascular parkinsonism: what makes it different?|url=https://pmj.bmj.com/content/87/1034/829|journal=Postgraduate Medical Journal|language=en|volume=87|issue=1034|pages=829–836|doi=10.1136/postgradmedj-2011-130051|issn=0032-5473|pmid=22121251}}</ref><ref name=":0" /><ref>{{Cite journal|last=Miguel-Puga|first=Adán|last2=Villafuerte|first2=Gabriel|last3=Salas-Pacheco|first3=José|last4=Arias-Carrión|first4=Oscar|date=2017-09-22|title=Therapeutic Interventions for Vascular Parkinsonism: A Systematic Review and Meta-analysis|url=http://journal.frontiersin.org/article/10.3389/fneur.2017.00481/full|journal=Frontiers in Neurology|volume=8|pages=481|doi=10.3389/fneur.2017.00481|issn=1664-2295|pmc=5614922|pmid=29018399}}</ref>


===Pathways involved in neurodegeneration===
Other identifiable causes of parkinsonism include infections and metabolic derangement. Several ] also may present with parkinsonism and are sometimes referred to as "atypical parkinsonism" or ] syndromes (illnesses with parkinsonism plus some other features distinguishing them from PD). They include ], ], ], and ] (DLB).<ref name="pmid15172778" /><ref name="pmid205063122">{{cite journal|vauthors=Nuytemans K, Theuns J, Cruts M, Van Broeckhoven C|date=July 2010|orig-year=18 May 2010|title=Genetic etiology of Parkinson disease associated with mutations in the SNCA, PARK2, PINK1, PARK7, and LRRK2 genes: a mutation update|journal=Human Mutation|volume=31|issue=7|pages=763–80|doi=10.1002/humu.21277|pmc=3056147|pmid=20506312}}</ref> Dementia with Lewy bodies is another synucleinopathy and it has close pathological similarities with PD, especially with the subset of PD cases with ] known as ]. The relationship between PD and DLB is complex and incompletely understood.<ref name="pmid191737622">{{cite journal|vauthors=Aarsland D, Londos E, Ballard C|date=April 2009|orig-year=28 January 2009|title=Parkinson's disease dementia and dementia with Lewy bodies: different aspects of one entity|journal=International Psychogeriatrics|volume=21|issue=2|pages=216–19|doi=10.1017/S1041610208008612|pmid=19173762}}</ref> They may represent parts of a continuum with variable distinguishing clinical and pathological features or they may prove to be separate diseases.<ref name="pmid191737622" />
{{See also|Neurodegeneration#Mechanisms}}
Three major pathways—], ], and mitochondrial maintenance—are known to be affected by and contribute to Parkinson's pathogenesis, with all three linked to alpha-synuclein.{{sfn|Vázquez-Vélez|Zoghbi|2021|pp=96-99}} High risk gene variants also impair all three of these processes.{{sfn|Vázquez-Vélez|Zoghbi|2021|pp=96-99}} All steps of vesicular trafficking are impaired by alpha-synuclein. It blocks ] (ER) vesicles from reaching the ]—leading to ]—and Golgi vesicles from reaching the ], preventing alpha-synuclein degradation and leading to its build-up.{{sfn|Vázquez-Vélez|Zoghbi|2021|pp=96-97}} Risky gene variants, chiefly ''GBA'', further compromise lysosomal function.{{sfn|Vázquez-Vélez|Zoghbi|2021|pp=98-99}} Although the mechanism is not well established, alpha-synuclein can impair mitochondrial function and cause subsequent ]. Mitochondrial dysfunction can in turn lead to further alpha-synuclein accumulation in a ].{{sfn|Vázquez-Vélez|Zoghbi|2021|p=99}} Microglial activation, possibly caused by alpha-synuclein, is also strongly indicated.{{sfn|Vázquez-Vélez|Zoghbi|2021|p=100}}{{sfn|Ye|Robak|Yu|Cykowski|2023|p=112}}


==Pathophysiology== ==Risk factors==
===Positive risk factors===
] (stained brown) in a brain cell of the ] in Parkinson's disease. The brown colour is positive ] staining for ].|alt=Several brain cells stained in blue. The largest one, a neurone, with an approximately circular form, has a brown circular body inside it. The brown body is about 40% the diameter of the cell in which it appears.]]
As 90 percent of Parkinson's cases are sporadic, the identification of the risk factors that may influence disease progression or severity is critical.{{sfn|Ascherio |Schwarzschild|2016|p=1257}}{{sfn|De Mirandaa|Goldmanb|Millerc|Greenamyred|2024|p=46}} The most significant risk factor in developing PD is age, with a prevalence of 1 percent in those aged over 65 and approximately 4.3 percent in age over 85.{{sfn|Coleman|Martin|2022|pp=2321-2322}} ] significant increases PD risk, especially if recent.{{sfn|Ascherio|Schwarzschild|2016|p=1260}}{{sfn|Delic|Beck|Pang|Citron|2020|pp=1-2}} Dairy consumption correlates with a higher risk, possibly due to contaminants like ].{{sfn|Ascherio |Schwarzschild|2016|p=1259}} Although the connection is unclear, ] diagnosis is associated with an approximately 45 percent risk increase.{{sfn|Ascherio |Schwarzschild|2016|p=1259}} There is also an association between ] use and PD risk.{{sfn|Ascherio|Schwarzschild|2016|p=1259}}
{{Main|Pathophysiology of Parkinson's disease}}


===Protective factors===
The main ] characteristics of PD are cell death in the brain's ] (affecting up to 70% of the ] neurons in the ] ] by the end of life).<ref name="pmid18398010"/> In Parkinson's disease, alpha-synuclein becomes ] and ] with other alpha-synuclein. Cells are unable to remove these clumps and the alpha synuclein becomes ], damaging the cells.<ref name=":9">{{Cite journal|last=Villar-Piqué|first=Anna|last2=Lopes da Fonseca|first2=Tomás|last3=Outeiro|first3=Tiago Fleming|date=October 2016|title=Structure, function and toxicity of alpha-synuclein: the Bermuda triangle in synucleinopathies|url=http://doi.wiley.com/10.1111/jnc.13249|journal=Journal of Neurochemistry|language=en|volume=139|pages=240–255|doi=10.1111/jnc.13249}}</ref><ref>{{Cite journal|last=Burré|first=Jacqueline|last2=Sharma|first2=Manu|last3=Südhof|first3=Thomas C.|date=1 March 2018|title=Cell Biology and Pathophysiology of α-Synuclein|url=https://pubmed.ncbi.nlm.nih.gov/28108534|journal=Cold Spring Harbor Perspectives in Medicine|volume=8|issue=3|doi=10.1101/cshperspect.a024091|issn=2157-1422|pmc=5519445|pmid=28108534}}</ref> These clumps can be seen in neurons under a microscope and are called ]. Loss of neurons is accompanied by the death of ]s (star-shaped ] cells) and a significant increase in the number of ] (another type of glial cell) in the substantia nigra.<ref name="Jankovic_book-Neuropathology">{{cite book|title=Parkinson's disease and movement disorders|publisher=Lippincott Williams & Wilkins|year=2007|isbn=978-0-7817-7881-7|veditors=Tolosa E, Jankovic JJ|location=Hagerstown, MD|pages=271–83|chapter=Neuropathology of movement disorders| vauthors = Dickson DV }}</ref> ] is a way to explain the progression of the parts of the brain affected by Parkinson's disease. According to this staging, PD starts in the medulla and the olfactory bulb before moving to the substantia nigra pars compacta and the rest of the midbrain/basal foerbrain. Movement symptom onset is associated when the disease begins to affect the substantia nigra pars compacta.<ref name=":1" />
]—a potent antioxidant—are associated with a lower risk of Parkinson's.]]
Although no compounds or activities have been mechanistically established as ] for Parkinson's,{{Sfn|Crotty|Schwarzschild|2020|p=1}}{{Sfn|Fabbri|Rascol|Foltynie|Carroll|2024|p=2}} several factors have been found to be associated with a decreased risk.{{Sfn|Crotty|Schwarzschild|2020|p=1}} ] and ] is strongly associated with a decreased risk, reducing the chance of developing PD by up to 70%.{{Sfn|Ascherio|Schwarzschild|2016|p=1262}}{{Sfn|Grotewolda|Albina|2024|pp=1–2}}{{sfn|Ascherio |Schwarzschild|2016|p=1259}} Various tobacco and smoke components have been hypothesized to be neuroprotective, including ], ], and ].{{Sfn|Grotewolda|Albina|2024|p=2}}{{Sfn|Rose|Schwarzschild|Gomperts|2024|pp=268—269}} Consumption of ], ], or ] is also strongly associated with neuroprotection.{{Sfn|Grotewolda|Albina|2024|p=3}}{{Sfn|Ren|Chen|2020|p=1}} Prescribed ] like ] may reduce risk.{{Sfn|Grotewolda|Albina|2024|p=3}}


Although findings have varied, usage of ] (NSAIDs) like ] may be neuroprotective.{{Sfn|Singh|Tripathi|Singh|2021|p=10}}{{Sfn|Ascherio|Schwarzschild|2016|pp=1265–1266}} ] may also have a protective effect, with a 22% risk reduction reported.{{Sfn|Lin|Pang|Li|Ou|2024|p=1}} Higher blood concentrations of ]—a potent ]—have been proposed to be neuroprotective.{{Sfn|Grotewolda|Albina|2024|p=2}}{{Sfn|Ascherio|Schwarzschild|2016|p=1263}} Although longitudinal studies observe a slight decrease in PD risk among those who consume ]—possibly due to alcohol's urate-increasing effect—alcohol abuse may increase risk.{{Sfn|Ascherio|Schwarzschild|2016|p=1261}}{{Sfn|Kamal|Tan|Ibrahim|Shaikh|2020|p=8}}
[[File:Journal.pone.0008247.g001.png|thumb|{{ordered list |list_style_type=upper-alpha
|1=<!--A-->Schematic initial progression of Lewy body deposits in the first stages of Parkinson's disease, as proposed by Braak and colleagues
|2=<!--B-->Localization of the area of significant brain ] in initial PD compared with a group of participants without the disease in a neuroimaging study, which concluded that ] damage may be the first identifiable stage of PD ]<ref name="pmid20011063">{{cite journal | vauthors = Jubault T, Brambati SM, Degroot C, Kullmann B, Strafella AP, Lafontaine AL, Chouinard S, Monchi O | title = Regional brain stem atrophy in idiopathic Parkinson's disease detected by anatomical MRI | journal = PLOS ONE | volume = 4 | issue = 12 | page = e8247 | date = December 2009 | pmid = 20011063 | pmc = 2784293 | doi = 10.1371/journal.pone.0008247 | veditors = Gendelman HE | bibcode = 2009PLoSO...4.8247J }}</ref>
}}|alt=Composite of three images, one in top row (referred to in caption as A), two in second row (referred to as B). Top shows a mid-line ] of the brainstem and ]. There are three circles superimposed along the brainstem and an arrow linking them from bottom to top and continuing upward and forward towards the frontal lobes of the brain. A line of text accompanies each circle: lower is "1. Dorsal Motor X Nucleus", middle is "2. Gain Setting Nuclei" and upper is "3. Substantia Nigra/Amygdala". The fourth line of text above the others says "4. ...". The two images at the bottom of the composite are magnetic resonance imaging (MRI) scans, one sagittal and the other transverse, centred at the same brain coordinates (x=-1, y=-36, z=-49). A colored blob marking volume reduction covers most of the brainstem.]]

There are five major pathways in the brain connecting other brain areas with the basal ganglia. These are known as the ], ], ], ] and ] circuits, with names indicating the main projection area of each circuit.<ref name="pmid18781672">{{cite journal | vauthors = Obeso JA, Rodríguez-Oroz MC, Benitez-Temino B, Blesa FJ, Guridi J, Marin C, Rodriguez M | title = Functional organization of the basal ganglia: therapeutic implications for Parkinson's disease | journal = Movement Disorders | volume = 23 Suppl 3 | issue = Suppl 3 | pages = S548–59 | year = 2008 | pmid = 18781672 | doi = 10.1002/mds.22062 | s2cid = 13186083 }}</ref> All of them are affected in PD, and their disruption explains many of the symptoms of the disease, since these circuits are involved in a wide variety of functions, including movement, attention and learning.<ref name="pmid18781672"/> Scientifically, the motor circuit has been examined the most intensively.<ref name="pmid18781672"/>

A particular conceptual model of the motor circuit and its alteration with PD has been of great influence since 1980, although some limitations have been pointed out which have led to modifications.<ref name="pmid18781672"/> In this model, the basal ganglia normally exert a constant inhibitory influence on a wide range of motor systems, preventing them from becoming active at inappropriate times. When a decision is made to perform a particular action, ] is reduced for the required motor system, thereby releasing it for activation. Dopamine acts to facilitate this release of inhibition, so high levels of dopamine function tend to promote motor activity, while low levels of dopamine function, such as occur in PD, demand greater exertions of effort for any given movement. Thus, the net effect of dopamine depletion is to produce ], an overall reduction in motor output.<ref name="pmid18781672"/> Drugs that are used to treat PD, conversely, may produce excessive dopamine activity, allowing motor systems to be activated at inappropriate times and thereby producing ]s.<ref name="pmid18781672"/>

===Brain cell death===
There is speculation of several mechanisms by which the brain cells could be lost.<ref name="pmid20495568">{{cite journal | vauthors = Obeso JA, Rodriguez-Oroz MC, Goetz CG, ''et al'' | title = Missing pieces in the Parkinson's disease puzzle | journal = Nature Medicine | volume = 16 | issue = 6 | pages = 653–61 | date = June 2010 | pmid = 20495568 | doi = 10.1038/nm.2165 | s2cid = 3146438 }}</ref> One mechanism consists of an abnormal accumulation of the protein ] bound to ] in the damaged cells. This insoluble ] accumulates inside neurons forming ] called Lewy bodies.<ref name="pmid18398010"/><ref name="pmid20563819">{{cite journal | vauthors = Schulz-Schaeffer WJ | title = The synaptic pathology of alpha-synuclein aggregation in dementia with Lewy bodies, Parkinson's disease and Parkinson's disease dementia | journal = Acta Neuropathologica | volume = 120 | issue = 2 | pages = 131–43 | date = August 2010 | pmid = 20563819 | pmc = 2892607 | doi = 10.1007/s00401-010-0711-0 }}</ref> According to the ], a classification of the disease based on pathological findings proposed by ], Lewy bodies first appear in the ], ] and ]; individuals at this stage may be asymptomatic or may have early non-motor symptoms (such as loss of sense of smell, or some sleep or automatic dysfunction). As the disease progresses, Lewy bodies develop in the substantia nigra, areas of the ] and basal ] and, finally, the ].<ref name="pmid18398010"/> These brain sites are the main places of neuronal degeneration in PD; however, Lewy bodies may not cause cell death and they may be protective (with the abnormal protein sequestered or walled off). Other forms of alpha-synuclein (e.g., ]s) that are not aggregated in Lewy bodies and ] may actually be the toxic forms of the protein.<ref name="pmid20495568"/><ref name="pmid20563819"/> In people with dementia, a generalized presence of Lewy bodies is common in cortical areas. ]s and ], characteristic of ], are not common unless the person is demented.<ref name="Jankovic_book-Neuropathology"/>

Other cell-death mechanisms include ] and ] system dysfunction and reduced ] activity.<ref name="pmid20495568"/> Iron accumulation in the substantia nigra is typically observed in conjunction with the protein inclusions. It may be related to ], ] and neuronal death, but the mechanisms are not fully understood.<ref name="pmid20082992">{{cite journal | vauthors = Hirsch EC | title = Iron transport in Parkinson's disease | journal = Parkinsonism & Related Disorders | volume = 15 Suppl 3 | issue = Suppl 3 | pages = S209–11 | date = December 2009 | pmid = 20082992 | doi = 10.1016/S1353-8020(09)70816-8 }}</ref>


==Diagnosis== ==Diagnosis==
Diagnosis of Parkinson's disease is largely clinical, relying on ] and examination of symptoms, with an emphasis on symptoms that appear in later stages.{{sfn|Armstrong|Okun|2020|p=548}}{{sfn|Rizzo|Copetti|Arcuti|Martino|2016|p=1}} Although early stage diagnosis is not reliable,{{sfn|Rizzo|Copetti|Arcuti|Martino|2016|p=1}}{{sfn|Ugrumov|2020|p=997}} prodromal diagnosis may consider previous family history of Parkinson's and possible early symptoms like ] (RBD), reduced sense of smell, and gastrointestinal issues.{{sfn|Armstrong|Okun|2020|p=551}} Isolated RBD is a particularly significant sign as 90% of those affected will develop some form of neurodegenerative parkinsonism.{{sfn|Tolosa|Garrido|Scholz|Poewe|2021|p=391}} Diagnosis in later stages requires the manifestation of parkinsonism, specifically bradykinesia and rigidity or tremor. Further support includes other motor and non-motor symptoms and genetic profiling.{{sfn|Armstrong|Okun|2020|pp=551-552}}
A physician will initially assess for Parkinson's disease with a careful ] and ].<ref name=Jankovic2008/> People may be given levodopa, with any resulting improvement in motor impairment helping to confirm the PD diagnosis. The finding of Lewy bodies in the midbrain on ] is usually considered final proof that the person had PD. The clinical course of the illness over time may reveal it is not Parkinson's disease, requiring that the clinical presentation be periodically reviewed to confirm accuracy of the diagnosis.<ref name=Jankovic2008/><ref name="Nice-Diagnosis">{{cite book| chapter=Diagnosing Parkinson's Disease| editor=The National Collaborating Centre for Chronic Conditions| title=Parkinson's Disease| chapter-url=http://guidance.nice.org.uk/CG35/Guidance/pdf/English| publisher=Royal College of Physicians| location=London| year=2006| isbn=978-1-86016-283-1| pages=29–47| url-status=live| archive-url=https://web.archive.org/web/20100924153546/http://guidance.nice.org.uk/CG35/Guidance/pdf/English| archive-date=24 September 2010| df=dmy-all}}</ref>

Other causes that can secondarily produce parkinsonism are ] and drugs.<ref name="Nice-Diagnosis"/> ]s such as ] and ] must be ].<ref name=Jankovic2008/> Anti-Parkinson's medications are typically less effective at controlling symptoms in Parkinson plus syndromes.<ref name=Jankovic2008/> Faster progression rates, early cognitive dysfunction or postural instability, minimal tremor or symmetry at onset may indicate a Parkinson plus disease rather than PD itself.<ref name="pmid12464118">{{cite journal | vauthors = Poewe W, Wenning G | title = The differential diagnosis of Parkinson's disease | journal = European Journal of Neurology | volume = 9 Suppl 3 | issue = Suppl 3 | pages = 23–30 | date = November 2002 | pmid = 12464118 | doi = 10.1046/j.1468-1331.9.s3.3.x }}</ref> Genetic forms with an autosomal ] or ] pattern of inheritance are sometimes referred to as familial Parkinson's disease or familial parkinsonism.<ref name="pmid15172778"/>

Medical organizations have created ] to ease and standardize the diagnostic process, especially in the early stages of the disease. The most widely known criteria come from the UK Queen Square Brain Bank for Neurological Disorders and the U.S. ]. The Queen Square Brain Bank criteria require slowness of movement (bradykinesia) plus either rigidity, resting tremor, or postural instability. Other possible causes of these symptoms need to be ruled out. Finally, three or more of the following supportive features are required during onset or evolution: unilateral onset, tremor at rest, progression in time, asymmetry of motor symptoms, response to levodopa for at least five years, clinical course of at least ten years and appearance of ]s induced by the intake of excessive levodopa.<ref>{{cite journal | vauthors = Gibb WR, Lees AJ | title = The relevance of the Lewy body to the pathogenesis of idiopathic Parkinson's disease | journal = Journal of Neurology, Neurosurgery, and Psychiatry | volume = 51 | issue = 6 | pages = 745–52 | date = June 1988 | pmid = 2841426 | pmc = 1033142 | doi = 10.1136/jnnp.51.6.745 }}</ref>

When PD diagnoses are checked by autopsy, movement disorders experts are found on average to be 79.6% accurate at initial assessment and 83.9% accurate after they have refined their diagnosis at a follow-up examination. When clinical diagnoses performed mainly by nonexperts are checked by autopsy, average accuracy is 73.8%. Overall, 80.6% of PD diagnoses are accurate, and 82.7% of diagnoses using the Brain Bank criteria are accurate.<ref>{{cite journal | vauthors = Rizzo G, Copetti M, Arcuti S, Martino D, Fontana A, Logroscino G | title = Accuracy of clinical diagnosis of Parkinson disease: A systematic review and meta-analysis | journal = Neurology | volume = 86 | issue = 6 | pages = 566–76 | date = February 2016 | pmid = 26764028 | doi = 10.1212/WNL.0000000000002350 | s2cid = 207110404 }}</ref>


A PD diagnosis is typically confirmed by two of the following criteria: responsiveness to levodopa, resting tremor, levodopa-induced dyskinesia, or with ].{{sfn|Armstrong|Okun|2020|pp=551-552}} If these criteria are not met, atypical parkinsonism is considered.{{sfn|Armstrong|Okun|2020|p=551}} However, definitive diagnoses can only be made post-mortem through pathological analysis.{{sfn|Rizzo|Copetti|Arcuti|Martino|2016|p=1}} Misdiagnosis is common, with a reported error rate of near 25 percent, and diagnoses often change during follow-ups.{{sfn|Rizzo|Copetti|Arcuti|Martino|2016|p=1}}{{sfn|Heim|Krismer|De Marzi|Seppi|2017|p=916}} Diagnosis can be further complicated by multiple overlapping conditions.{{sfn|Rizzo|Copetti|Arcuti|Martino|2016|p=1}}
A task force of the ] (MDS) has proposed diagnostic criteria for Parkinson’s disease as well as research criteria for the diagnosis of ] disease, but these will require validation against the more established criteria.<ref>{{cite journal | vauthors = Postuma RB, Berg D, Stern M, Poewe W, Olanow CW, Oertel W, Obeso J, Marek K, Litvan I, Lang AE, Halliday G, Goetz CG, Gasser T, Dubois B, Chan P, Bloem BR, Adler CH, Deuschl G | title = MDS clinical diagnostic criteria for Parkinson's disease | journal = Movement Disorders | volume = 30 | issue = 12 | pages = 1591–1601 | date = October 2015 | pmid = 26474316 | doi = 10.1002/mds.26424 | s2cid = 35567298 | url = https://semanticscholar.org/paper/4be7f3e8f8142247599eba69bacd9630bcb66a88 }}</ref><ref>{{cite journal | vauthors = Berg D, Postuma RB, Adler CH, Bloem BR, Chan P, Dubois B, Gasser T, Goetz CG, Halliday G, Joseph L, Lang AE, Liepelt-Scarfone I, Litvan I, Marek K, Obeso J, Oertel W, Olanow CW, Poewe W, Stern M, Deuschl G | title = MDS research criteria for prodromal Parkinson's disease | journal = Movement Disorders | volume = 30 | issue = 12 | pages = 1600–11 | date = October 2015 | pmid = 26474317 | doi = 10.1002/mds.26431 | s2cid = 206248344 | url = https://escholarship.org/content/qt2v885924/qt2v885924.pdf?t=nz28bb }}</ref>


===Imaging=== ===Imaging===
] ] uptake in the ] of a Parkinson's patient, captured through ]]]
] (CT) scans of people with PD usually appear normal.<ref name="pmid20351351">{{cite journal | vauthors = Brooks DJ | title = Imaging approaches to Parkinson disease | journal = Journal of Nuclear Medicine | volume = 51 | issue = 4 | pages = 596–609 | date = April 2010 | pmid = 20351351 | doi = 10.2967/jnumed.108.059998 | doi-access = free }}</ref> ] has become more accurate in diagnosis of the disease over time, specifically through iron-sensitive ] and ] sequences at a magnetic field strength of at least 3T, both of which can demonstrate absence of the characteristic 'swallow tail' imaging pattern in the ] ].<ref>{{cite journal | vauthors = Schwarz ST, Afzal M, Morgan PS, Bajaj N, Gowland PA, Auer DP | title = The 'swallow tail' appearance of the healthy nigrosome – a new accurate test of Parkinson's disease: a case-control and retrospective cross-sectional MRI study at 3T | journal = PLOS ONE | volume = 9 | issue = 4 | page = e93814 | date = 2014 | pmid = 24710392 | pmc = 3977922 | doi = 10.1371/journal.pone.0093814 | bibcode = 2014PLoSO...993814S }}</ref> In a meta-analysis, absence of this pattern was highly ] and ] for the disease.<ref>{{cite journal | vauthors = Mahlknecht P, Krismer F, Poewe W, Seppi K | title = Meta-analysis of dorsolateral nigral hyperintensity on magnetic resonance imaging as a marker for Parkinson's disease | journal = Movement Disorders | volume = 32 | issue = 4 | pages = 619–23 | date = April 2017 | pmid = 28151553 | doi = 10.1002/mds.26932 | s2cid = 7730034 }}</ref> A 2020 meta-analysis found that ] had a favorable diagnostic performance in discriminating individuals with Parkinson's from healthy subjects.<ref>{{cite journal | vauthors = Cho SJ, Bae YJ, Kim JM, et al | title = Diagnostic performance of neuromelanin-sensitive magnetic resonance imaging for patients with Parkinson's disease and factor analysis for its heterogeneity: a systematic review and meta-analysis | journal = European Radiology | volume = 30 | issue = 10 | pages = 1–13 | date = September 2020 | pmid = 32886201 | doi = 10.1007/s00330-020-07240-7 | s2cid = 221478854}}</ref> ] has shown potential in distinguishing between PD and Parkinson plus syndromes, though its diagnostic value is still under investigation.<ref name="pmid20351351"/> CT and MRI are also used to rule out other diseases that can be secondary causes of parkinsonism, most commonly ] and ], as well as less frequent entities such as basal ganglia ] and ].<ref name="pmid20351351"/>
Diagnosis can be aided by molecular imaging techniques such as ] (MRI), ] (PET), and ] (SPECT).{{sfn|Bidesi|Andersen|Windhorst|Shalgunov|2021|p=660}} As both conventional MRI and ] (CT) scans are usually normal in patients with early PD, they can be used to exclude other pathologies that cause parkinsonism.{{sfn|Heim|Krismer|De Marzi|Seppi|2017|p=916}}{{sfn|Brooks|2010|p=597}} ] can differentiate PD from ] (MSA).{{sfn|Tolosa|Garrido|Scholz|Poewe|2021|p=392}} Emerging MRI techniques of at least 3.0 T ]—including ], ], and ]—may detect abnormalities in the substantia nigra, nigrostriatal pathway, and elsewhere.{{sfn|Heim|Krismer|De Marzi|Seppi|2017|p=916}}


Unlike MRI, PET and SPECT use ] for imaging.{{sfn|Bidesi|Andersen|Windhorst|Shalgunov|2021|p=665}} Both techniques can aid diagnosis by characterizing PD-associated alterations in the metabolism and ] of dopamine in the basal ganglia.{{sfn|Suwijn|van Boheemen|de Haan|Tissingh|2015}}{{sfn|Bidesi|Andersen|Windhorst|Shalgunov|2021|pp=664-672}} Largely used outside the United States, iodine-123-meta-iodobenzylguanidine ] ] can assess heart muscle denervation to support a PD diagnosis.{{sfn|Armstrong|Okun|2020|p=552}}
The ] of ]s in the basal ganglia can be directly measured with ] and ] scans, with the ] being a common proprietary version of this study. It has shown high agreement with clinical diagnoses of Parkinson's.<ref>{{cite journal | vauthors = Suwijn SR, van Boheemen CJ, de Haan RJ, Tissingh G, Booij J, de Bie RM | title = The diagnostic accuracy of dopamine transporter SPECT imaging to detect nigrostriatal cell loss in patients with Parkinson's disease or clinically uncertain parkinsonism: a systematic review | journal = EJNMMI Research | volume = 5 | page = 12 | date = 2015 | pmid = 25853018 | pmc = 4385258 | doi = 10.1186/s13550-015-0087-1 }}</ref> Reduced dopamine-related activity in the basal ganglia can help exclude drug-induced Parkinsonism. This finding is not entirely specific, however, and can be seen with both PD and Parkinson-plus disorders.<ref name="pmid20351351"/> In the United States, DaTSCANs are only ] approved to distinguish Parkinson’s disease or Parkinsonian syndromes from ].<ref>{{cite web |title=DaTSCAN Approval Letter |url=https://www.accessdata.fda.gov/drugsatfda_docs/label/2011/022454Orig1s000Lbl.pdf |website=FDA.gov |publisher=Food and Drug Administration |access-date=22 March 2019}}</ref>


===Differential diagnosis=== ===Differential diagnosis===
] with MRI]]
Other conditions that can have similar presentations to PD include:<ref name=Greenland2018>{{cite book |last1=Greenland |first1=Julia C. |last2=Stoker |first2=Thomas B. | name-list-style = vanc |title=Parkinson's Disease: Pathogenesis and Clinical Aspects |date=2018 |publisher=Codon Publications |isbn=978-0-9944381-6-4 |pages=109–28 }}</ref>
{{See also|Parkinson-plus syndrome}}
{{refbegin|2}}
] of Parkinson's is among the most difficult in ].{{sfn|Heim|Krismer|De Marzi|Seppi|2017|p=915}} Differentiating early PD from atypical parkinsonian disorders is a major difficulty. In their initial stages, PD can be difficult to distinguish from the atypical neurodegenerative parkinsonisms, including MSA, dementia with Lewy bodies, and the ] ] and ].{{sfn|Tolosa|Garrido|Scholz|Poewe|2021|p=389}}{{sfn|Caproni|Colosimo|2020|p=21}} Other conditions that may present similarly to PD include vascular parkinsonism, ], and ].{{sfn|Tolosa|Garrido|Scholz|Poewe|2021|p=390}}{{sfn|Caproni|Colosimo|2020|pp=15, 21}}
* ]
* ]
* ]
* ]
* Drug induced parkinsonism
* ]
* ]
* ]
* ]
* ]
* ]
* ]
* Obsessional slowness
* ]
* Psychogenic parkinsonism
* ]
* ]
* Vascular parkinsonism
{{refend}}


The International Parkinson and Movement Disorder Society has proposed a set of criteria that, unlike the standard Queen's Square Brain Bank Criteria, includes non-exclusionary "red-flag" clinical features that may not suggest Parkinson's.{{sfn|Tolosa|Garrido|Scholz|Poewe|2021|pp=390-391}} A large number of "red flags" have been proposed and adopted for various conditions that might mimic the symptoms of PD.{{sfn|Caproni|Colosimo|2020|p=14}} Diagnostic tests, including gene sequencing, molecular imaging techniques, and assessment of smell may also distinguish PD.{{sfn|Tolosa|Garrido|Scholz|Poewe|2021|p=392}} MRI is particularly powerful due to several unique features for atypical parkinsonisms.{{sfn|Tolosa|Garrido|Scholz|Poewe|2021|p=392}} Key distinguishing symptoms and features include:{{sfn|Tolosa|Garrido|Scholz|Poewe|2021|p=391}}{{Sfn|Simon|Greenberg|Aminoff|2017}}{{Sfn|Greenland|Barker|2018}}
==Prevention==
Exercise in middle age may reduce the risk of Parkinson's disease later in life.<ref name=Neuro2011/> ] also appears protective with a greater decrease in risk occurring with a larger intake of caffeinated beverages such as coffee.<ref name="pmid20182023">{{cite journal | vauthors = Costa J, Lunet N, Santos C, Santos J, Vaz-Carneiro A | title = Caffeine exposure and the risk of Parkinson's disease: a systematic review and meta-analysis of observational studies | journal = Journal of Alzheimer's Disease | volume = 20 Suppl 1 | issue = Suppl 1 | pages = S221–38 | year = 2010 | pmid = 20182023 | doi = 10.3233/JAD-2010-091525 | doi-access = free }}</ref> People who smoke cigarettes or use ] are less likely than non-smokers to develop PD, and the more they have used tobacco, the less likely they are to develop PD. It is not known what underlies this effect. Tobacco use may actually protect against PD, or it may be that an unknown factor both increases the risk of PD and causes an aversion to tobacco or makes it easier to stop using tobacco.<ref>{{cite journal | vauthors = Ma C, Liu Y, Neumann S, Gao X | title = Nicotine from cigarette smoking and diet and Parkinson disease: a review | journal = Translational Neurodegeneration | volume = 6 | page = 18 | date = 2017 | pmid = 28680589 | pmc = 5494127 | doi = 10.1186/s40035-017-0090-8 }}</ref><ref>{{cite journal |vauthors=Dorsey ER, Sherer T, Okun MS, Bloem BR |title=The Emerging Evidence of the Parkinson Pandemic |journal=J Parkinsons Dis |volume=8 |issue=s1 |pages=S3–8 |date=2018 |pmid=30584159 |pmc=6311367 |doi=10.3233/JPD-181474 |type=Review}}</ref>


{| class="wikitable plainrowheaders"
]s, such as ] and ], have been proposed to protect against the disease, but results of studies have been contradictory and no positive effect has been proven.<ref name="pmid16713924"/> The results regarding fat and ]s have been contradictory, with various studies reporting protective effects, risk-increasing effects or no effects.<ref name="pmid16713924"/> There have been preliminary indications that the use of ] drugs and ]s may be protective.<ref name="Lancet2015" /> A 2010 ] found that ]s (apart from ]), have been associated with at least a 15 percent (higher in long-term and regular users) reduction in the incidence of the development of Parkinson's disease.<ref name="Gagne-2010">{{cite journal | vauthors = Gagne JJ, Power MC | title = Anti-inflammatory drugs and risk of Parkinson disease: a meta-analysis | journal = Neurology | volume = 74 | issue = 12 | pages = 995–1002 | date = March 2010 | pmid = 20308684 | pmc = 2848103 | doi = 10.1212/WNL.0b013e3181d5a4a3 }}</ref>
|-
!scope="col" | Disorder
!scope="col" | Distinguishing symptoms and features
|-
! scope="row" | ]
| Levodopa resistance, ], ], corticosensory loss, ], ], and ]
|-
! scope="row" | ]
| Levodopa resistance, cognitive predominance before motor symptoms, and fluctuating cognitive symptoms
|-
! scope="row" | ]
| Tremor that worsens with action, normal SPECT scan
|-
! scope="row" | ]
| Levodopa resistance, rapidly progressive, autonomic failure, stridor, present ], cerebellar ataxia, and specific MRI findings like the "Hot Cross Bun"
|-
! scope="row" | ]
| Levodopa resistance, restrictive vertical gaze, ], ], specific MRI findings, and early and different postural difficulties
|-
|}


==Management== ==Management==
{{Main|Management of Parkinson's disease}} {{Main|Management of Parkinson's disease}}
As of 2024, no disease-modifying therapies exist that reverse or slow neurodegeneration, processes respectively termed neurorestoration and neuroprotection.{{Sfn|Crotty|Schwarzschild|2020|p=1}}{{Sfn|Fabbri|Rascol|Foltynie|Carroll|2024|p=2}} Patients are typically managed with a holistic approach that combines lifestyle modifications with ].{{sfn|Connolly|Lang|2014}} Current pharmacological interventions purely target symptoms, by either increasing endogenous ] levels or directly mimicking dopamine's effect on the patient's brain.{{sfn|de Bie|Clarke|Espay|Fox|2020|p=3}}{{sfn|Connolly|Lang|2014}} These include dopamine agonists, MAO-B inhibitors, and levodopa: the most widely used and effective drug.{{sfn|de Bie|Clarke|Espay|Fox|2020|pp=1, 3}}{{sfn|Connolly|Lang|2014}} The optimal time to initiate pharmacological treatment is debated,{{sfn|Kobylecki|2020|p=395}} but initial dopamine agonist and MAO-B inhibitor treatment and later levodopa therapy is common.{{sfn|de Bie|Clarke|Espay|Fox|2020|p=4}} Invasive procedures such as ] may be used for patients that do not respond to medication.{{sfn|Limousin|Foltynie|2019|p=234}}{{sfn|Bronstein|Tagliati|Alterman|Lozano|2011|p=169}}
]
There is no cure for Parkinson's disease. Medications, surgery, and ] may provide relief, improve the quality of a persons life, and are much more effective than treatments available for other neurological disorders like Alzheimer’s disease, ], and ]s.<ref name=":3" /> The main families of drugs useful for treating motor symptoms are ] (always combined with a ] and sometimes also with a ], ]s and ]. The stage of the disease and the age at disease onset determine which group is most useful.<ref name=":3">{{cite journal | vauthors = Connolly BS, Lang AE | title = Pharmacological treatment of Parkinson disease: a review | journal = JAMA | volume = 311 | issue = 16 | pages = 1670–83 | date = 30 April 2014 | pmid = 24756517 | doi = 10.1001/jama.2014.3654 | s2cid = 205058847 | url = https://semanticscholar.org/paper/282b19727fa648f2fdc92597a40713d3708ae092 }}</ref>

] of Parkinson's disease gives six stages, that can be used to identify early stages, later stages, and late stages.<ref name=":4" /> The initial stage in which some disability has already developed and requires pharmacological treatment is followed by later stages associated with the development of complications related to levodopa usage, and a third stage when symptoms unrelated to dopamine deficiency or levodopa treatment may predominate.<ref name=":4">{{Cite book|title=Parkinson's Disease : Non-Motor and Non-Dopaminergic Features|date=2011|publisher=Wiley-Blackwell|chapter=The non-motor and non-dopaminergic fratures of PD|others=Olanow, C. Warren., Stocchi, Fabrizio., Lang, Anthony E.|isbn=978-1405191852|oclc=743205140}}</ref>

Treatment in the first stage aims for an optimal ] between symptom control and treatment side-effects. The start of levodopa treatment may be postponed by initially using other medications such as MAO-B inhibitors and dopamine agonists instead, in the hope of delaying the onset of complications due to levodopa use.<ref name="Nice-pharma">{{cite book| chapter=Symptomatic pharmacological therapy in Parkinson's disease| editor=The National Collaborating Centre for Chronic Conditions| title=Parkinson's Disease| chapter-url=http://guidance.nice.org.uk/CG35/Guidance/pdf/English| publisher=Royal College of Physicians| location=London| year=2006| isbn=978-1-86016-283-1| pages=59–100| url-status=live| archive-url=https://web.archive.org/web/20100924153546/http://guidance.nice.org.uk/CG35/Guidance/pdf/English| archive-date=24 September 2010| df=dmy-all}}</ref> However, levodopa is still the most effective treatment for the motor symptoms of PD and should not be delayed in people when their quality of life is impaired. Levodopa-related dyskinesias correlate more strongly with duration and severity of the disease than duration of levodopa treatment, so delaying this therapy may not provide much longer dyskinesia-free time than early use.<ref>{{cite journal | vauthors = Zhang J, Tan LC | title = Revisiting the Medical Management of Parkinson's Disease: Levodopa versus Dopamine Agonist | journal = Current Neuropharmacology | volume = 14 | issue = 4 | pages = 356–63 | date = 2016 | pmid = 26644151 | pmc = 4876591 | doi = 10.2174/1570159X14666151208114634 }}</ref>

In later stages the aim is to reduce PD symptoms while controlling fluctuations in the effect of the medication. Sudden withdrawals from medication or its overuse have to be managed.<ref name="Nice-pharma" /> When oral medications are not enough to control symptoms, surgery, ], subcutaneous waking day ] infusion and ] dopa pumps may be useful.<ref name=Pedrosa2013/> Late stage PD presents many challenges requiring a variety of treatments including those for psychiatric symptoms particularly ], ], bladder dysfunction and ].<ref name=Pedrosa2013>{{cite journal | vauthors = Pedrosa DJ, Timmermann L | title = Review: management of Parkinson's disease | journal = Neuropsychiatric Disease and Treatment | volume = 9 | pages = 321–40 | date = 2013 | pmid = 23487540 | pmc = 3592512 | doi = 10.2147/NDT.S32302 |type= Review}}</ref> In the final stages of the disease, ] is provided to improve a person's quality of life.<ref name="Nice-palliative">{{cite book | chapter=Palliative care in Parkinson's disease | editor=The National Collaborating Centre for Chronic Conditions | title=Parkinson's Disease | chapter-url=http://guidance.nice.org.uk/CG35/Guidance/pdf/English | publisher=Royal College of Physicians | location=London | year=2006 | isbn=978-1-86016-283-1 | pages=147–51 | url-status=live | archive-url=https://web.archive.org/web/20100924153546/http://guidance.nice.org.uk/CG35/Guidance/pdf/English | archive-date=24 September 2010 | df=dmy-all }}</ref>


===Medications=== ===Medications===
{{update|reason= {{PMID|32171387}} |date=October 2020}}

====Levodopa==== ====Levodopa====
]/]/]) pills contain a cocktail of the dopamine precursor <small>L</small>-DOPA and COMT and AAAD inhibitors.]]
The motor symptoms of PD are the result of reduced dopamine production in the brain's basal ganglia. Dopamine does not cross the ], so it cannot be taken as a medicine to boost the brain's depleted levels of dopamine. However a ] of dopamine, levodopa, can pass through to the brain where it is readily converted to dopamine, and administration of levodopa temporarily diminishes the motor symptoms of PD. Levodopa has been the most widely used PD treatment for over 40 years.<ref name="Nice-pharma"/>
] (<small>L</small>-DOPA) is the most widely used and the most effective therapy—the ]—for Parkinson's treatment.{{sfn|de Bie|Clarke|Espay|Fox|2020|pp=1, 3}} The compound occurs naturally and is the immediate precursor for dopamine synthesis in the dopaminergic neurons of the substantia nigra.{{sfn|Tambasco|Romoli|Calabresi|2018|p=1239}} Levodopa administration reduces the dopamine deficiency, alleviating parkinsonian symptoms.{{sfn|LeWitt|Fahn|2016|p=S5-S6}}{{sfn|Tambasco|Romoli|Calabresi|2018|pp=1239-1240}}


Despite its efficacy, levodopa poses several challenges and has been called the "pharmacologist's nightmare".{{sfn|Tambasco|Romoli|Calabresi|2018|p=1240}}{{sfn|Leta|Klingelhoefer|Longardner|Campagnolo|2023|p=1466}} Its metabolism outside the brain by ] (AAAD) and ] (COMT) can cause nausea and vomiting; inhibitors like ], ], and ] are usually taken with levodopa to mitigate these effects.{{sfn|Leta|Klingelhoefer|Longardner|Campagnolo|2023|pp=1466-1468}}{{sfn|Tambasco|Romoli|Calabresi|2018|p=1241}}{{efn|group=note|These inhibitors do not cross the ] and thus do not prevent levodopa metabolism there.{{sfn|Leta|Klingelhoefer|Longardner|Campagnolo|2023|p=1468}}}} Symptoms may become unresponsive to levodopa, with sudden changes between a state of mobility ("ON time") and immobility ("OFF time").{{sfn|Jing|Yang|Taximaimaiti|Wang|2023|p=1224}} Long-term levodopa use may also ] and motor fluctuations. Although this often causes levodopa use to be delayed to later stages, earlier administration leads to improved motor function and quality of life.{{sfn|de Bie|Clarke|Espay|Fox|2020|pp=1, 3-4}}
Only 5–10% of levodopa crosses the blood–brain barrier. Much of the remainder is metabolized to dopamine elsewhere in the body, causing a variety of side effects including ], vomiting and ].<ref>{{Cite book|page=10|title=Levodopa pharmacokinetics – from stomach to brain A study on patients with Parkinson's disease.|last=Maria|first=Nord | name-list-style = vanc |date=2017|publisher=Linköping University Electronic Press|isbn=978-9176855577|location=Linköping|oclc=993068595}}</ref> ] and ] are ] which do not cross the blood-brain barrier and inhibit the conversion of levodopa to dopamine outside the brain, reducing side effects and improving the availability of levodopa for passage into the brain. One of these drugs is usually taken along with levodopa, often combined with levodopa in the same pill.<ref name= Oertel2017>{{cite journal | vauthors = Oertel WH | title = Recent advances in treating Parkinson's disease | journal = F1000Research | volume = 6 | page = 260 | date = 13 March 2017 | pmid = 28357055 | pmc = 5357034 | doi = 10.12688/f1000research.10100.1 |type= Review}}</ref>

Levodopa-use leads in the long term to the development of complications: involuntary movements called ]s, and fluctuations in the effectiveness of the medication.<ref name="Nice-pharma"/> When fluctuations occur, a person can cycle through phases with good response to medication and reduced PD symptoms ("on" state), and phases with poor response to medication and significant PD symptoms ("off" state).<ref name="Nice-pharma" /> Using lower doses of levodopa may reduce the risk and severity of these levodopa-induced complications.<ref>{{cite journal | vauthors = Aquino CC, Fox SH | title = Clinical spectrum of levodopa-induced complications | journal = Movement Disorders | volume = 30 | issue = 1 | pages = 80–89 | date = January 2015 | pmid = 25488260 | doi = 10.1002/mds.26125 | s2cid = 22301199 }}</ref> A former strategy to reduce levodopa-related dyskinesia and fluctuations was to withdraw levodopa medication for some time. This is now discouraged since it can bring on dangerous side effects such as ].<ref name="Nice-pharma"/> Most people with PD will eventually need levodopa and will later develop levodopa-induced fluctuations and dyskinesias.<ref name="Nice-pharma" />

There are ] versions of levodopa. Older controlled-release levodopa preparations have poor and unreliable ] and ] and have not demonstrated improved control of PD motor symptoms or a reduction in levodopa-related complications when compared to immediate release preparations. A newer extended-release levodopa preparation does seem to be more effective in reducing fluctuation,s but in many people problems persist. Intestinal infusions of levodopa (Duodopa) can result in striking improvements in fluctuations compared to oral levodopa when the fluctuations are due to insufficient uptake caused by ]. Other oral, longer acting formulations are under study and other modes of delivery (inhaled, transdermal) are being developed.<ref name=Oertel2017/>

====COMT inhibitors====
]
During the course of Parkinson's disease, affected people can experience what's known as a "wearing off phenomena" where they have a recurrence of symptoms after a dose of levodopa but right before their next dose.<ref name=":1">{{Cite journal|last=Armstrong|first=Melissa J.|last2=Okun|first2=Michael S.|date=2020-02-11|title=Diagnosis and Treatment of Parkinson Disease: A Review|url=https://jamanetwork.com/journals/jama/fullarticle/2760741|journal=JAMA|language=en|volume=323|issue=6|pages=548|doi=10.1001/jama.2019.22360|issn=0098-7484}}</ref> Catechol-O-methyltransferase (COMT), is a protein that degrades levodopa before it can cross the ] and these inhibitors allow for more levodopa to cross.<ref name=":2">{{Cite journal|last=Akhtar|first=Md Jawaid|last2=Yar|first2=M. Shahar|last3=Grover|first3=Gourav|last4=Nath|first4=Rajarshi|date=January 2020|title=Neurological and psychiatric management using COMT inhibitors: A review|url=https://pubmed.ncbi.nlm.nih.gov/31708229|journal=Bioorganic Chemistry|volume=94|pages=103418|doi=10.1016/j.bioorg.2019.103418|issn=1090-2120|pmid=31708229|doi-access=free}}</ref> They are normally not used in the management of early symptoms however can be used in conjunction with levodopa/carbidopa when a person is experiencing the "wearing off phenomena" with their motor symptoms.<ref name=":1" />

There are three COMT inhibitors available to treat adults with Parkinson’s Disease and end-of-dose motor fluctuations: ], ] and ].<ref name=":1" /> Tolcapone has been available for several years however its usefulness is limited by possible liver damage complications and therefore requires liver function monitoring.<ref>{{Cite web|title=Tasmar 100 mg Tablets - Summary of Product Characteristics (SmPC) - (emc)|url=https://www.medicines.org.uk/emc/product/3902|access-date=2021-01-07|website=www.medicines.org.uk}}</ref><ref name=":0" /><ref name=":1" /><ref name=":2" /> Entacapone and opicapone have not been showed to cause significant alterations to liver function.<ref name=":2" /><ref>{{Cite journal|last=Scott|first=Lesley J.|date=September 2016|title=Opicapone: A Review in Parkinson's Disease|url=https://pubmed.ncbi.nlm.nih.gov/27498199|journal=Drugs|volume=76|issue=13|pages=1293–1300|doi=10.1007/s40265-016-0623-y|issn=1179-1950|pmid=27498199}}</ref><ref>{{Cite journal|last=Watkins|first=P.|date=2000|title=COMT inhibitors and liver toxicity|url=https://pubmed.ncbi.nlm.nih.gov/11147510|journal=Neurology|volume=55|issue=11 Suppl 4|pages=S51–52; discussion S53–56|issn=0028-3878|pmid=11147510}}</ref> Licensed preparations of entacapone contain entacapone alone or in combination with carbidopa and levodopa.<ref>{{Cite web|title=Comtess 200 mg film-coated Tablets - Summary of Product Characteristics (SmPC) - (emc)|url=https://www.medicines.org.uk/emc/product/1632|access-date=2021-01-07|website=www.medicines.org.uk}}</ref><ref name=":0" /><ref>{{Cite web|title=Stalevo 150 mg/37.5 mg/200 mg Film-coated Tablets - Summary of Product Characteristics (SmPC) - (emc)|url=https://www.medicines.org.uk/emc/product/6517/smpc|access-date=2021-01-07|website=www.medicines.org.uk}}</ref> Opicapone is a once-daily COMT inhibitor.<ref>{{Cite web|title=Ongentys 50 mg hard capsules - Summary of Product Characteristics (SmPC) - (emc)|url=https://www.medicines.org.uk/emc/product/7386|access-date=2021-01-07|website=www.medicines.org.uk}}</ref><ref name=":1" />


====Dopamine agonists==== ====Dopamine agonists====
] are an alternative or complement for levodopa therapy. They activate dopamine receptors in the striatum, with reduced risk of motor fluctuations and dyskinesia.{{sfn|Jing|Yang|Taximaimaiti|Wang|2023|p=1225}} ] dopamine agonists were commonly used, but have been largely replaced with non-ergot compounds due to severe adverse effects like ] and cardiovascular issues.{{sfn|Jing|Yang|Taximaimaiti|Wang|2023|p=1225}} Non-ergot agonists are efficacious in both early and late stage Parkinson's,{{sfn|Jing|Yang|Taximaimaiti|Wang|2023|p=1226}} The agonist ] is often used for drug-resistant OFF time in later-stage PD.{{sfn|Jing|Yang|Taximaimaiti|Wang|2023|p=1226}}{{sfn|Kobylecki|2020|p=396}} However, after five years of use, impulse control disorders may occur in over 40 percent of PD patients taking dopamine agonists.{{sfn|Kobylecki|2020|p=395}} A problematic, narcotic-like withdrawal effect may occur when agonist use is reduced or stopped.{{sfn|Kobylecki|2020|p=395}}{{sfn|de Bie|Clarke|Espay|Fox|2020|p=1}} Compared to levodopa, dopamine agonists are more likely to cause fatigue, daytime sleepiness, and hallucinations.{{sfn|de Bie|Clarke|Espay|Fox|2020|p=1}}
Several ]s that bind to dopamine receptors in the brain have similar effects to levodopa.<ref name="Nice-pharma"/> These were initially used as a complementary therapy to levodopa for individuals experiencing levodopa complications (on-off fluctuations and dyskinesias); they are now mainly used on their own as first therapy for the motor symptoms of PD with the aim of delaying the initiation of levodopa therapy and so delaying the onset of levodopa's complications.<ref name="Nice-pharma" /><ref>{{cite journal | vauthors = Goldenberg MM | title = Medical management of Parkinson's disease | journal = P & T | volume = 33 | issue = 10 | pages = 590–606 | date = October 2008 | pmid = 19750042 | pmc = 2730785 }}</ref> Dopamine agonists include ], ], ], ], ], ], ] and ].

Though dopamine agonists are less effective than levodopa at controlling PD motor symptoms, they are usually effective enough to manage these symptoms in the first years of treatment.<ref name="pmid15172778"/> Dyskinesias due to dopamine agonists are rare in younger people who have PD but, along with other complications, become more common with older age at onset.<ref name="pmid15172778"/> Thus dopamine agonists are the preferred initial treatment for younger onset PD, and levodopa is preferred for older onset PD.<ref name="pmid15172778"/>

Dopamine agonists produce significant, although usually mild, side effects including ], hallucinations, insomnia, nausea, and constipation.<ref name="Nice-pharma"/> Sometimes side effects appear even at a minimal clinically effective dose, leading the physician to search for a different drug.<ref name="Nice-pharma" /> Agonists have been related to impulse control disorders (such as compulsive sexual activity, eating, gambling and shopping) even more strongly than levodopa.<ref name="pmid20123548">{{cite journal | vauthors = Ceravolo R, Frosini D, Rossi C, Bonuccelli U | title = Impulse control disorders in Parkinson's disease: definition, epidemiology, risk factors, neurobiology and management | journal = Parkinsonism & Related Disorders | volume = 15 Suppl 4 | issue = Suppl 4 | pages = S111–15 | date = December 2009 | pmid = 20123548 | doi = 10.1016/S1353-8020(09)70847-8 }}</ref> They tend to be more expensive than levodopa.<ref name="pmid15172778"/>

], a non-orally administered dopamine agonist, may be used to reduce off periods and dyskinesia in late PD.<ref name="Nice-pharma"/> It is administered by intermittent injections or continuous ].<ref name="Nice-pharma" /> Since secondary effects such as confusion and hallucinations are common, individuals receiving apomorphine treatment should be closely monitored.<ref name="Nice-pharma" /> Two dopamine agonists that are administered through skin patches (] and ]) and are useful for people in the initial stages and possibly to control off states in those in the advanced state.<ref name="Jankovic_book-Pharma">{{cite book|title=Parkinson's disease and movement disorders|publisher=Lippincott Williams & Wilkins|year=2007|isbn=978-0-7817-7881-7|veditors=Tolosa E, Jankovic JJ|location=Hagerstwon, MD|pages=110–45|chapter=Pharmacological management of Parkinson's disease|vauthors=Tolosa E, Katzenschlager R}}</ref>


====MAO-B inhibitors==== ====MAO-B inhibitors====
] (], ] and ]) increase the amount of dopamine in the basal ganglia by inhibiting the activity of ] (MAO-B), an enzyme which breaks down dopamine.<ref name="Nice-pharma"/> Like dopamine agonists, their use may delay the commencement of levodopa therapy in early disease, but MAO-B inhibitors produce more adverse effects and are less effective than levodopa at controlling PD motor symptoms. There are few studies of their effectiveness in the advanced stage, although results suggest that they are useful to reduce fluctuations between on and off periods.<ref name="Nice-pharma" /> An initial study indicated that selegiline in combination with levodopa increased the risk of death, but this was later disproven.<ref name="Nice-pharma" /> MAO-B inhibitors—such as ], ] and ]—increase the amount of dopamine in the basal ganglia by inhibiting the activity of ], an enzyme that breaks down dopamine.{{sfn|Robakis|Fahn|2015|pp=433-434}} These compounds mildly alleviate motor symptoms when used as monotherapy but can also be used with levodopa and can be used at any disease stage.{{sfn|Robakis|Fahn|2015|p=433}} When used with levodopa, time spent in the off phase is reduced.{{Sfn|Binde|Tvete|Gåsemyr|Natvig|2018|p=1924}}{{sfn|Tan|Jenner|Chen|2022|p=477}} Selegiline has been shown to delay the need for initial levodopa, suggesting that it might be neuroprotective and slow the progression of the disease.{{sfn|Alborghetti|Nicoletti|2019}} Common side effects are nausea, dizziness, insomnia, sleepiness, and (in selegiline and rasagiline) orthostatic hypotension.{{sfn|Alborghetti|Nicoletti|2019}}{{sfn|Armstrong|Okun|2020}} MAO-Bs are known to increase serotonin and cause a potentially dangerous condition known as ].{{sfn|Alborghetti|Nicoletti|2019}}{{sfn|Robakis|Fahn|2015|p=435}}


====Other drugs==== ====Other drugs====
Treatments for non-motor symptoms of PD have not been well studied and many medications are used ].{{sfn|Tanner|Ostrem|2024}} A diverse range of symptoms beyond those related to motor function can be treated pharmaceutically.{{sfn|The National Collaborating Centre for Chronic Conditions}} Examples include ] for cognitive impairment and ] for ].{{sfn|Seppi|Ray Chaudhuri|Coelho|Fox|2019|pp=183, 185, 188}} ], ] and ] are commonly used off label for orthostatic hypotension related to autonomic dysfunction. Sublingual ] or ] injections may be used off-label for drooling. ] and ] are often used for depression related to PD, but there is a risk of ] with the SSRI or SNRI antidepressants.{{sfn|Tanner|Ostrem|2024}} Doxepin and rasagline may reduce physical fatigue in PD.{{sfn|Elbers|Verhoef|van Wegen|Berendse|2015}} Other treatments have received government approval, such as the first FDA-approved treatment for PD psychosis, ]. Although its efficacy is inferior to off-label ], it has significantly fewer side effects.{{sfn|Rissardo|Durante|Sharon|Caprara|2022|p=1}}
Other drugs such as ] and ]s may be useful as treatment of motor symptoms. However, the evidence supporting them lacks quality, so they are not first choice treatments.<ref name="Nice-pharma" /><ref>{{cite journal | vauthors = Crosby N, Deane KH, Clarke CE | title = Amantadine in Parkinson's disease | journal = The Cochrane Database of Systematic Reviews | issue = 1 | page = CD003468 | date = 2003 | pmid = 12535476 | doi = 10.1002/14651858.CD003468 }}</ref> In addition to motor symptoms, PD is accompanied by a diverse range of symptoms. A number of drugs have been used to treat some of these problems.<ref name="Nice-NonMotor">{{cite book|chapter=Non-motor features of Parkinson's disease|editor=The National Collaborating Centre for Chronic Conditions|title=Parkinson's Disease|chapter-url=http://guidance.nice.org.uk/CG35/Guidance/pdf/English|publisher=Royal College of Physicians|location=London|year=2006|isbn=978-1-86016-283-1|pages=113–33|url-status=live|archive-url=https://web.archive.org/web/20100924153546/http://guidance.nice.org.uk/CG35/Guidance/pdf/English|archive-date=24 September 2010}}</ref> Examples are the use of ] for psychosis, ] for dementia, and ] for ].<ref name="Nice-NonMotor" /><ref name="pmid19559160">{{cite journal | vauthors = Hasnain M, Vieweg WV, Baron MS, Beatty-Brooks M, Fernandez A, Pandurangi AK | title = Pharmacological management of psychosis in elderly patients with parkinsonism | journal = The American Journal of Medicine | volume = 122 | issue = 7 | pages = 614–22 | date = July 2009 | pmid = 19559160 | doi = 10.1016/j.amjmed.2009.01.025 }}</ref> In 2016 ] was approved for the management of Parkinson's disease psychosis.<ref>{{cite press release |title=FDA approves first drug to treat hallucinations and delusions associated with Parkinson's disease |url=https://www.fda.gov/newsevents/newsroom/pressannouncements/ucm498442.htm |website=www.fda.gov |access-date=12 October 2018 |date= 29 April 2016}}</ref>

Doxepin and rasagline may reduce physical fatigue in PD.<ref name= Elbers2015>{{cite journal | vauthors = Elbers RG, Verhoef J, van Wegen EE, Berendse HW, Kwakkel G | title = Interventions for fatigue in Parkinson's disease | journal = The Cochrane Database of Systematic Reviews | issue = 10 | page = CD010925 | date = October 2015 | pmid = 26447539 | doi = 10.1002/14651858.CD010925.pub2 |type= Review}}</ref>


===Surgery=== ===Invasive interventions===
{{Further|Deep brain stimulation}}
].]]
].]]
Treating motor symptoms with surgery was once a common practice, but since the discovery of levodopa, the number of operations has declined.<ref name="Nice-surgery">{{cite book|chapter=Surgery for Parkinson's disease|editor=The National Collaborating Centre for Chronic Conditions|title=Parkinson's Disease|chapter-url=http://guidance.nice.org.uk/CG35/Guidance/pdf/English|publisher=Royal College of Physicians|location=London|year=2006|isbn=978-1-86016-283-1|pages=101–11|url-status=live|archive-url=https://web.archive.org/web/20100924153546/http://guidance.nice.org.uk/CG35/Guidance/pdf/English|archive-date=24 September 2010}}</ref> Studies in the past few decades have led to great improvements in surgical techniques, so that surgery is again being used in people with advanced PD for whom drug therapy is no longer sufficient.<ref name="Nice-surgery" /> Surgery for PD can be divided in two main groups: lesional and ] (DBS). Target areas for DBS or lesions include the ], the ] or the ].<ref name="Nice-surgery" /> Deep brain stimulation is the most commonly used surgical treatment, developed in the 1980s by ] and others. It involves the implantation of a medical device called a ], which sends electrical impulses to specific parts of the brain. DBS is recommended for people who have PD with motor fluctuations and tremor inadequately controlled by medication, or to those who are intolerant to medication, as long as they do not have severe ] problems.<ref name="pmid20937936">{{cite journal | vauthors = Bronstein JM, Tagliati M, Alterman RL, et al| title = Deep brain stimulation for Parkinson disease: an expert consensus and review of key issues | journal = Archives of Neurology | volume = 68 | issue = 2 | page = 165 | date = February 2011 | pmid = 20937936 | pmc = 4523130 | doi = 10.1001/archneurol.2010.260 }}</ref> Other, less common, surgical therapies involve intentional formation of lesions to suppress overactivity of specific ] areas. For example, ] involves surgical destruction of the globus pallidus to control dyskinesia.<ref name="Nice-surgery" />
Surgery for Parkinson's first appeared in the 19th century and by the 1960s had evolved into ] that lesioned the ], ] or ] (a ]).{{sfn|Lozano|Tam|Lozano|2018|pp=1-2}} The discovery of <small>L</small>-DOPA for PD treatment caused ablative therapies to largely disappear.{{sfn|Lozano|Tam|Lozano|2018|p=2}}{{sfn|Bronstein|Tagliati|Alterman|Lozano|2011|p=165}} Ablative surgeries experienced a resurgence in the 1990s but were quickly superseded by newly-developed ] (DBS).{{sfn|Bronstein|Tagliati|Alterman|Lozano|2011|p=165}} Although ] and ] surgeries have been developed for pallidotomies and ], their use remains rare.{{sfn|Lozano|Tam|Lozano|2018|p=6}}{{sfn|Moosa|Martínez-Fernández|Elias|Del Alamo|2019|pp=1244-1249}}


DBS involves the implantation of ] called ]s, which sends electrical impulses to specific parts of the brain.{{sfn|Limousin|Foltynie|2019|p=234}} DBS for the ] and ] has high efficacy for up to 2 years, but longterm efficacy is unclear and likely decreases with time.{{sfn|Limousin|Foltynie|2019|p=234}} DBS typically targets rigidity and tremor,{{sfn|Bronstein|Tagliati|Alterman|Lozano|2011|p=168}} and is recommended for PD patients who are intolerant or do not respond to medication.{{sfn|Bronstein|Tagliati|Alterman|Lozano|2011|p=169}} Cognitive impairment is the most common exclusion criteria.{{sfn|Bronstein|Tagliati|Alterman|Lozano|2011|p=166}}
Four areas of the brain have been treated with neural stimulators in PD.<ref name=Dallapiazza2018>{{cite book | vauthors = Dallapiazza RF, Vloo PD, Fomenko A, et al| date = 2018 | chapter = Considerations for Patient and Target Selection in Deep Brain Stimulation surgery for Parkinson’s disease | veditors = Stoker TB, Greenland JC | title = Parkinson's disease: Pathogenesis and clinical aspects. | location = Brisbane | publisher = Codon Publications }}</ref> These are the ], ], ] and the ]. DBS of the globus pallidus interna improves motor function while DBS of the thalamic DBS improves tremor but has little effect on bradykinesia or rigidity. DBS of the subthalamic nucleus is usually avoided if a history of depression or neurocognitive impairment is present. DBS of the subthalamic nucleus is associated with reduction in medication. Pedunculopontine nucleus DBS remains experimental at present. Generally DBS is associated with 30–60% improvement in motor score evaluations.{{citation needed|date=August 2020}}


===Rehabilitation=== ===Rehabilitation===
{{Further|Rehabilitation in Parkinson's disease}} {{Further|Management of Parkinson's disease#Rehabilitation}}
] ride of this PD patient, is often recommended.]]
Exercise programs are recommended in people with Parkinson's disease.<ref name=Neuro2011/> There is some evidence that speech or mobility problems can improve with rehabilitation, although studies are scarce and of low quality.<ref name="Nice-rehab">{{cite book|chapter=Other key interventions|editor=The National Collaborating Centre for Chronic Conditions|title=Parkinson's Disease|chapter-url=http://guidance.nice.org.uk/CG35/Guidance/pdf/English|publisher=Royal College of Physicians|location=London|year=2006|isbn=978-1-86016-283-1|pages=135–46|url-status=live|archive-url=https://web.archive.org/web/20100924153546/http://guidance.nice.org.uk/CG35/Guidance/pdf/English|archive-date=24 September 2010}}</ref><ref name="pmid18181210">{{cite journal | vauthors = Goodwin VA, Richards SH, Taylor RS, Taylor AH, Campbell JL | title = The effectiveness of exercise interventions for people with Parkinson's disease: a systematic review and meta-analysis | journal = Movement Disorders | volume = 23 | issue = 5 | pages = 631–40 | date = April 2008 | pmid = 18181210 | doi = 10.1002/mds.21922 | url = https://semanticscholar.org/paper/2d8f7fdb1698e642f375c876181cbfee96ed45e8 | hdl = 10871/17451 | s2cid = 3808899 | hdl-access = free }}</ref> Regular ] with or without ] can be beneficial to maintain and improve mobility, flexibility, strength, gait speed, and quality of life.<ref name="pmid18181210" /> When an exercise program is performed under the supervision of a physiotherapist, there are more improvements in motor symptoms, mental and emotional functions, daily living activities, and quality of life compared to a self-supervised exercise program at home.<ref>{{cite journal | vauthors = Dereli EE, Yaliman A | title = Comparison of the effects of a physiotherapist-supervised exercise programme and a self-supervised exercise programme on quality of life in patients with Parkinson's disease | journal = Clinical Rehabilitation | volume = 24 | issue = 4 | pages = 352–62 | date = April 2010 | pmid = 20360152 | doi = 10.1177/0269215509358933 | s2cid = 10947269 }}</ref> In terms of improving flexibility and range of motion for people experiencing ], generalized relaxation techniques such as gentle rocking have been found to decrease excessive muscle tension. Other effective techniques to promote relaxation include slow rotational movements of the extremities and trunk, rhythmic initiation, ], and ] techniques.<ref>{{harvnb|O'Sullivan|Schmitz|2007|pp=873, 876}}</ref> As for gait and addressing the challenges associated with the disease such as ] (slowness of movement), shuffling and decreased arm swing; physiotherapists have a variety of strategies to improve functional mobility and safety. Areas of interest with respect to gait during rehabilitation programs focus on, but are not limited to improving gait speed, the base of support, stride length, trunk and arm swing movement. Strategies include utilizing assistive equipment (pole walking and treadmill walking), verbal cueing (manual, visual and auditory), exercises (marching and PNF patterns) and altering environments (surfaces, inputs, open vs. closed).<ref>{{harvnb|O'Sullivan|Schmitz|2007|p=879}}</ref> Strengthening exercises have shown improvements in strength and motor function for people with primary muscular weakness and weakness related to inactivity with mild to moderate Parkinson's disease. However, reports show a significant interaction between strength and the time the medications was taken. Therefore, it is recommended that people with PD should perform exercises 45 minutes to one hour after medications when they are at their best.<ref>{{harvnb|O'Sullivan|Schmitz|2007|p=877}}</ref> Also, due to the forward flexed posture, and respiratory dysfunctions in advanced Parkinson's disease, deep diaphragmatic breathing exercises are beneficial in improving chest wall mobility and vital capacity.<ref>{{harvnb|O'Sullivan|Schmitz|2007|p=880}}</ref> Exercise may improve constipation.<ref name="pmid19691125"/> It is unclear if exercise reduces physical fatigue in PD.<ref name=Elbers2015/>
Although pharmacological therapies can improve symptoms, patients' autonomy and ability to perform everyday tasks is still reduced by PD. As a result, rehabilitation is often useful. However, the scientific support for any single rehabilitation treatment is limited.{{sfn|Tofani|Ranieri|Fabbrini|Berardi|2020|p=891}}


Exercise programs are often recommended, with preliminary evidence of efficacy.{{sfn|Ernst|Folkerts|Gollan|Lieker|2023}}{{Sfn|Crotty|Schwarzschild|2020|pp=1—2}}{{sfn|Ahlskog|2011|p=292}} Regular ] with or without physical therapy can be beneficial to maintain and improve mobility, flexibility, strength, gait speed, and quality of life.{{sfn|Ernst|Folkerts|Gollan|Lieker|2023}} Aerobic, mind-body, and resistance training may be beneficial in alleviating PD-associated depression and anxiety.{{sfn|Ahlskog|2011|p=292}}{{sfn|Costa|Prati|de Oliveira|Brito|2024}} ] may increase ] and strength, facilitating daily tasks that require grasping objects.{{sfn|Ramazzina|Bernazzoli|Costantino|2017|pp=620-623}}
One of the most widely practiced ] disorders associated with Parkinson's disease is the ] (LSVT).<ref name="Nice-rehab" /><ref name="pmid17117354">{{cite journal | vauthors = Fox CM, Ramig LO, Ciucci MR, Sapir S, McFarland DH, Farley BG | title = The science and practice of LSVT/LOUD: neural plasticity-principled approach to treating individuals with Parkinson disease and other neurological disorders | journal = Seminars in Speech and Language | volume = 27 | issue = 4 | pages = 283–99 | date = November 2006 | pmid = 17117354 | doi = 10.1055/s-2006-955118 }}</ref> Speech therapy and specifically LSVT may improve speech.<ref name="Nice-rehab" /> ] (OT) aims to promote health and quality of life by helping people with the disease to participate in as many of their ] as possible.<ref name="Nice-rehab" /> There have been few studies on the effectiveness of OT and their quality is poor, although there is some indication that it may improve motor skills and quality of life for the duration of the therapy.<ref name="Nice-rehab" /><ref name="pmid17636709">{{cite journal | vauthors = Dixon L, Duncan D, Johnson P, ''et al'' | title = Occupational therapy for patients with Parkinson's disease | journal = The Cochrane Database of Systematic Reviews | issue = 3 | page = CD002813 | date = July 2007 | pmid = 17636709 | doi = 10.1002/14651858.CD002813.pub2 | pmc = 6991932 }}</ref>


In improving flexibility and range of motion for people experiencing rigidity, generalized relaxation techniques such as gentle rocking have been found to decrease excessive muscle tension. Other effective techniques to promote relaxation include slow rotational movements of the extremities and trunk, rhythmic initiation, ], and ].{{Sfn|O'Sullivan|Schmitz|2007|pp=873, 876}} Deep diaphragmatic breathing may also improve chest-wall mobility and ] decreased by the stooped posture and respiratory dysfunctions of advanced Parkinson's.{{Sfn|O'Sullivan|Schmitz|2007|p=880}} Rehabilitation techniques targeting gait and the challenges posed by bradykinesia, shuffling, and decreased arm swing include ], ], and ] exercises.{{Sfn|O'Sullivan|Schmitz|2007|p=879}}
===Palliative care===
] is specialized medical care for people with serious illnesses, including Parkinson's. The goal of this speciality is to improve quality of life for both the person with Parkinson's and the family by providing relief from the symptoms, pain, and stress of illnesses.<ref name="pmid17531914">{{cite journal | vauthors = Ferrell B, Connor SR, Cordes A, ''et al'' | title = The national agenda for quality palliative care: the National Consensus Project and the National Quality Forum | journal = Journal of Pain and Symptom Management | volume = 33 | issue = 6 | pages = 737–44 | date = June 2007 | pmid = 17531914 | doi = 10.1016/j.jpainsymman.2007.02.024 | doi-access = free }}</ref> As Parkinson's is not a curable disease, all treatments are focused on slowing decline and improving quality of life, and are therefore palliative in nature.<ref name="pmid24182372">{{cite book | vauthors = Lorenzl S, Nübling G, Perrar KM, Voltz R | chapter = Palliative treatment of chronic neurologic disorders | volume = 118 | pages = 133–39 | year = 2013 | pmid = 24182372 | doi = 10.1016/B978-0-444-53501-6.00010-X | isbn = 978-0444535016 | series = Handbook of Clinical Neurology | title = Ethical and Legal Issues in Neurology }}</ref>


] such as the ] may reduce the effect of speech disorders associated with PD.{{sfn|McDonnell|Rischbieth|Schammer|Seaforth|2018|pp=607-609}}{{sfn|Pu|Huang|Kong|Wang|2021|pp=1-2}} ] is another rehabilitation strategy and can improve quality of life by enabling PD patients to find engaging activities and communal roles, adapt to their living environment, and improving domestic and work abilities.{{sfn|Tofani|Ranieri|Fabbrini|Berardi|2020|pp=891, 900}}
Palliative care should be involved earlier, rather than later in the disease course.<ref name="pmid22771241">{{cite journal | vauthors = Ghoche R | title = The conceptual framework of palliative care applied to advanced Parkinson's disease | journal = Parkinsonism & Related Disorders | volume = 18 Suppl 3 | issue = Suppl 3 | pages = S2–5 | date = December 2012 | pmid = 22771241 | doi = 10.1016/j.parkreldis.2012.06.012 }}</ref><ref name="pmid20081638">{{cite journal | vauthors = Wilcox SK | title = Extending palliative care to patients with Parkinson's disease | journal = British Journal of Hospital Medicine | volume = 71 | issue = 1 | pages = 26–30 | date = January 2010 | pmid = 20081638 | doi = 10.12968/hmed.2010.71.1.45969 }}</ref> Palliative care specialists can help with physical symptoms, emotional factors such as loss of function and jobs, depression, fear, and existential concerns.<ref name="pmid22771241" /><ref name="pmid20081638" /><ref name="pmid24801658">{{cite journal | vauthors = Moens K, Higginson IJ, Harding R | title = Are there differences in the prevalence of palliative care-related problems in people living with advanced cancer and eight non-cancer conditions? A systematic review | journal = Journal of Pain and Symptom Management | volume = 48 | issue = 4 | pages = 660–77 | date = October 2014 | pmid = 24801658 | doi = 10.1016/j.jpainsymman.2013.11.009 | doi-access = free }}</ref>


===Diet===
Along with offering emotional support to both the affected person and family, palliative care serves an important role in addressing goals of care. People with Parkinson's may have many difficult decisions to make as the disease progresses such as wishes for ], ], and ]; wishes for or against ]; and when to use ] care.<ref name="pmid24182372" /> Palliative care team members can help answer questions and guide people with Parkinson's on these complex and emotional topics to help them make the best decision based on their own values.<ref name="pmid20081638" /><ref name="pmid24195263">{{cite journal | vauthors = Casey G | title = Parkinson's disease: a long and difficult journey | journal = Nursing New Zealand | volume = 19 | issue = 7 | pages = 20–24 | date = August 2013 | pmid = 24195263 }}</ref>
Parkinson's poses digestive problems like constipation and ], and a balanced diet with periodical nutritional assessments is recommended to avoid weight loss or gain and minimize the consequences of gastrointestinal dysfunction. In particular, a Mediterranean diet is advised and may slow disease progression.{{sfn|Lister|2020|pp=99-100}}{{sfn|Barichella|Cereda|Pezzoli|2009|pp=1888}} As it can compete for uptake with ] derived from protein, levodopa should be taken 30 minutes before meals to minimize such competition. Low protein diets may also be needed by later stages.{{sfn|Barichella|Cereda|Pezzoli|2009|pp=1888}} As the disease advances, swallowing difficulties often arise. Using ]s for liquid intake and an upright posture when eating may be useful; both measures reduce the risk of choking. ] can be used to deliver food directly into the stomach.{{sfn|Barichella|Cereda|Pezzoli|2009|pp=1887}}{{sfn|Pasricha|Guerrero-Lopez|Kuo|2024|p=212}} Increased water and fiber intake is used to treat constipation.{{sfn|Pasricha|Guerrero-Lopez|Kuo|2024|p=216}}


===Palliative care===
Muscles and nerves that control the digestive process may be affected by PD, resulting in ] and ] (food remaining in the stomach for a longer period than normal).<ref name="pmid19691125"/> A balanced diet, based on periodical nutritional assessments, is recommended and should be designed to avoid weight loss or gain and minimize consequences of gastrointestinal dysfunction.<ref name="pmid19691125"/> As the disease advances, swallowing difficulties (]) may appear. In such cases it may be helpful to use ]s for liquid intake and an upright posture when eating, both measures reducing the risk of choking. ] to deliver food directly into the stomach is possible in severe cases.<ref name="pmid19691125"/>
As Parkinson's is incurable, palliative care aims to improve the quality of life for both the patient and family by alleviating the symptoms and stress associated with illness.{{sfn|Ghoche|2012|pp=S2-S3}}{{sfn|Wilcox|2010|p=26}}{{sfn|Ferrell|Connor|Cordes|Dahlin|2007|p=741}} Early integration of palliative care into the disease course is recommended, rather than delaying until later stages.{{sfn|Ghoche|2012|pp=S2-S3}} Palliative care specialists can help with physical symptoms, emotional factors such as loss of function and jobs, depression, fear, as well as existential concerns.{{sfn|Ghoche|2012|p=S3}} Palliative care team members also help guide patients and families on difficult decisions caused by disease progression, such as wishes for a ], ] or ], use of ], and entering ] care.{{sfn|Casey|2013|pp=20-22}}{{sfn|Bernat|Beresford|2013|pp=135, 137, 138}}

Levodopa and ]s use the same transportation system in the intestine and the blood–brain barrier, thereby competing for access.<ref name="pmid19691125"/> When they are taken together, this results in a reduced effectiveness of the drug.<ref name="pmid19691125"/> Therefore, when levodopa is introduced, excessive ] is discouraged and well balanced ] is recommended. In advanced stages, additional intake of low-protein products such as bread or pasta is recommended for similar reasons.<ref name="pmid19691125"/> To minimize interaction with proteins, levodopa should be taken 30 minutes before meals.<ref name="pmid19691125"/> At the same time, regimens for PD restrict proteins during breakfast and lunch, allowing protein intake in the evening.<ref name="pmid19691125"/>


==Prognosis== ==Prognosis==
{{See also|Unified Parkinson's disease rating scale}} {{See also|Unified Parkinson's disease rating scale}}
{| class="wikitable" style="float:right; margin-left:1em; font-size:90%; line-height:1.4em; width:350px;"
]s per 100,000&nbsp;inhabitants in 2004
|+ Prognosis of PD subtypes{{sfn|Corcoran|Kluger|2021|p=956}}{{sfn|Fereshtehnejad|Zeighami|Dagher|Postuma|2017|p=1967}}
{{Col-begin}}
! rowspan="2" style="background:#011E41;color:white;text-align:center;" |Parkinson's subtype
{{Col-break}}
! colspan="2" style="background:#011E41;color:white;text-align:center;" |Mean years post-diagnosis until:
{{legend|#b3b3b3|no data}}
|-
{{legend|#ffff65|<&nbsp;5}}
! style="background:#011E41;color:white;" |Severe cognitive or movement abnormalities{{efn|group=note|Defined as the onset of development of recurrent falls, wheelchair dependence, dementia, or facility placement.{{sfn|Corcoran|Kluger|2021|p=956}}}}
{{legend|#fff200|5–12.5}}
! style="background:#011E41;color:white;" |Death
{{legend|#ffdc00|12.5–20}}
|-
{{legend|#ffc600|20–27.5}}
! Mild-motor predominant
{{legend|#ffb000|27.5–35}}
|style="text-align:center;"| 14.3
{{legend|#ff9a00|35–42.5}}
|style="text-align:center;"| 20.2
{{Col-break}}
|-
{{legend|#ff8400|42.5–50}}
! Intermediate
{{legend|#ff6e00|50–57.5}}
|style="text-align:center;"| 8.2
{{legend|#ff5800|57.5–65}}
|style="text-align:center;"| 13.1
{{legend|#ff4200|65–72.5}}
|-
{{legend|#ff2c00|72.5–80}}
! Diffuse malignant
{{legend|#cb0000|>&nbsp;80}}
|style="text-align:center;"| 3.5
{{col-end}}]]
|style="text-align:center;"| 8.1
|-
|}
As Parkinson's is a ] with multiple ], prognostication can be difficult and prognoses can be highly variable.{{sfn|Corcoran|Kluger|2021|p=956}}{{sfn|Tolosa|Garrido|Scholz|Poewe|2021|p=385}} On average, life expectancy is reduced in those with Parkinson's, with younger age of onset resulting in greater life expectancy decreases.{{sfn|Dommershuijsen|Darweesh|Ben-Shlomo|Kluger|2023|pp=2–3}} Although PD subtype categorization is controversial, the 2017 Parkinson's Progression Markers Initiative study identified three broad scorable subtypes of increasing severity and more rapid progression: mild-motor predominant, intermediate, and diffuse malignant. Mean years of survival post-diagnosis were 20.2, 13.1, and 8.1.{{sfn|Corcoran|Kluger|2021|p=956}}


Around 30% of Parkinson's patients develop dementia, and is 12 times more likely to occur in elderly patients of those with severe PD.{{sfn|Murueta-Goyena|Muiño|Gómez-Esteban|2017|p=26}} Dementia is less likely to arise in patients with tremor-dominant PD.{{sfn|Murueta-Goyena|Muiño|Gómez-Esteban|2017|p=27}} Parkinson's disease dementia is associated with a reduced ] in people with PD and their ]s, increased mortality, and a higher probability of needing ].{{sfn|Caballol|Martí|Tolosa|2007|p=S358}}
PD invariably progresses with time. A severity rating method known as the ] (UPDRS) is the most commonly used metric for clinical study. A modified version known as the MDS-UPDRS is also sometimes used. An older scaling method known as the ] (originally published in 1967), and a similar scale known as the Modified Hoehn and Yahr scale, have also been commonly used. The Hoehn and Yahr scale defines five basic stages of progression.


The incidence rate of falls in Parkinson's patients is approximately 45 to 68%, thrice that of healthy individuals, and half of such falls result in serious secondary injuries. Falls increase ] and ].{{sfn|Murueta-Goyena|Muiño|Gómez-Esteban|2024|p=395}} Around 90% of those with PD develop ], which worsens with disease progression and can hinder communication.{{sfn|Atalar|Oguz|Genc|2023|p=163}} Additionally, over 80% of PD patients develop dysphagia: consequent inhalation of gastric and oropharyngeal secretions can lead to ].{{sfn|Chua|Wang|Chan|Chan|2024|p=1}} Aspiration pneumonia is responsible for 70% of deaths in those with PD.{{sfn|Corcoran|Muiño|Kluger|2021|p=1}}
Motor symptoms, if not treated, advance aggressively in the early stages of the disease and more slowly later. Untreated, individuals are expected to lose independent ] after an average of eight years and be bedridden after ten years.<ref name="pmid17131223" /> However, it is uncommon to find untreated people nowadays. Medication has improved the prognosis of motor symptoms, while at the same time it is a new source of disability, because of the undesired effects of levodopa after years of use.<ref name="pmid17131223" /> In people taking levodopa, the progression time of symptoms to a stage of high dependency from caregivers may be over 15 years.<ref name="pmid17131223" /> However, it is hard to predict what course the disease will take for a given individual.<ref name="pmid17131223" /> Age is the best predictor of disease progression.<ref name="pmid20495568"/> The rate of motor decline is greater in those with less impairment at the time of diagnosis, while cognitive impairment is more frequent in those who are over 70 years of age at symptom onset.<ref name="pmid20495568"/>


==Epidemiology==
Since current therapies improve motor symptoms, disability at present is mainly related to non-motor features of the disease.<ref name="pmid20495568"/> Nevertheless, the relationship between disease progression and disability is not linear. Disability is initially related to motor symptoms.<ref name="pmid17131223">{{cite journal | vauthors = Poewe W | title = The natural history of Parkinson's disease | journal = Journal of Neurology | volume = 253 Suppl 7 | issue = Suppl 7 | pages = vii2–vii6| date = December 2006 | pmid = 17131223 | doi = 10.1007/s00415-006-7002-7 | s2cid = 35082340 }}</ref> As the disease advances, disability is more related to motor symptoms that do not respond adequately to medication, such as swallowing/speech difficulties, and gait/balance problems; and also to levodopa-induced complications, which appear in up to 50% of individuals after 5 years of levodopa usage.<ref name="pmid17131223" /> Finally, after ten years most people with the disease have autonomic disturbances, sleep problems, mood alterations and cognitive decline.<ref name="pmid17131223" /> All of these symptoms, especially cognitive decline, greatly increase disability.<ref name="pmid20495568"/><ref name="pmid17131223" />
], possibly due to exposure to pesticides and industrial waste.]]
As of 2024, Parkinson's is the second most common neurodegenerative disease and the fastest-growing in total number of cases.{{Sfn|Ben-Shlomo|Darweesh|Llibre-Guerra|Marras|2024|p=283}}{{Sfn|Varden|Walker|O'Callaghan|2024|p=1}} As of 2023, global ] was estimated to be 1.51 per 1000.{{Sfn|Zhu|Cui|Zhang|Yan|2024|p=e464}} Although it is around 40% more common in men,{{Sfn|Ben-Shlomo|Darweesh|Llibre-Guerra|Marras|2024|p=286}} age is the dominant predeterminant of Parkinson's.{{Sfn|Deliz|Tanner|Gonzalez-Latapi|2024|p=166}} Consequently, as ] has increased, Parkinson's disease prevalence has also risen, with an estimated increase in cases by 74% from 1990 to 2016.{{Sfn|Ben-Shlomo|Darweesh|Llibre-Guerra|Marras|2024|p=284}} The total number is predicted to rise to over 12 million patients by 2040.{{Sfn|Dorsey|Sherer|Okun|Bloem|2018|p=S4}} Some label this a ].{{Sfn|Ben-Shlomo|Darweesh|Llibre-Guerra|Marras|2024|p=284}}


This increase may be due to a number of global factors, including prolonged life expectancy, increased industrialisation, and ].{{Sfn|Ben-Shlomo|Darweesh|Llibre-Guerra|Marras|2024|p=284}} Although genetics is the sole factor in a minority of cases, most cases of Parkinson's are likely a result of ]: ] with ] have found Parkinson's ] to be just 30%.{{Sfn|Ben-Shlomo|Darweesh|Llibre-Guerra|Marras|2024|p=286}} The influence of multiple genetic and environmental factors complicates epidemiological efforts.{{Sfn|Deliz|Tanner|Gonzalez-Latapi|2024|p=165}}
The ] of people with PD is reduced.<ref name="pmid17131223" /> ] are around twice those of unaffected people.<ref name="pmid17131223" /> Cognitive decline and dementia, old age at onset, a more advanced disease state and presence of swallowing problems are all mortality ]s. On the other hand, a disease pattern mainly characterized by tremor as opposed to rigidity predicts an improved survival.<ref name="pmid17131223" /> Death from ] is twice as common in individuals with PD as in the healthy population.<ref name="pmid17131223" />


Relative to Europe and North America, disease prevalence is lower in Africa but similar in Latin America.{{Sfn|Ben-Shlomo|Darweesh|Llibre-Guerra|Marras|2024|p=285}} Although China is predicted to have nearly half of the global Parkinson's population by 2030,{{Sfn|Li|Ma|Cui|He|2019|p=1}} estimates of prevalence in Asia vary.{{Sfn|Ben-Shlomo|Darweesh|Llibre-Guerra|Marras|2024|p=285}} Potential explanations for these geographic differences include genetic variation, environmental factors, ], and life expectancy.{{Sfn|Ben-Shlomo|Darweesh|Llibre-Guerra|Marras|2024|p=285}} Although PD incidence and prevalence may vary by race and ethnicity, significant disparities in care, diagnosis, and study participation limit ] and lead to conflicting results.{{Sfn|Ben-Shlomo|Darweesh|Llibre-Guerra|Marras|2024|p=285}}{{Sfn|Deliz|Tanner|Gonzalez-Latapi|2024|p=165}} Within the United States, high rates of PD have been identified in the ], the ], and agricultural regions of other states: collectively termed the "PD belt".{{Sfn|Deliz|Tanner|Gonzalez-Latapi|2024|pp=164–165}} The association between rural residence and Parkinson's has been hypothesized to be caused by environmental factors like herbicides, pesticides, and industrial waste.{{Sfn|Deliz|Tanner|Gonzalez-Latapi|2024|pp=164–165}}{{Sfn|Huang|Bargues-Carot|Riaz|Wickham|2022|pp=1–2}}
In 2016 PD resulted in about 211,000 deaths globally, an increase of 161% since 1990.<ref name=GlobalBurden2016>{{cite journal |title=Global, regional, and national burden of neurological disorders, 1990-2016: a systematic analysis for the Global Burden of Disease Study 2016 |journal=Lancet Neurol |volume=18 |issue=5 |pages=459–80 |date=May 2019 |pmid=30879893 |pmc=6459001 |doi=10.1016/S1474-4422(18)30499-X |vauthors= Feigin VL, Nichols E, Alam T, et al}}</ref> The death rate increased by 19% to 1.81 per 100,000 people during that time.<ref name=GlobalBurden2016/>

==Epidemiology==
]
PD is the second most common ] after ] and affects approximately seven million people globally and one million people in the United States.<ref name="OFP">{{cite journal | vauthors = Yao SC, Hart AD, Terzella MJ |title=An evidence-based osteopathic approach to Parkinson disease |journal=Osteopathic Family Physician |volume=5 |issue=3 |pages=96–101 |date=May 2013 |doi=10.1016/j.osfp.2013.01.003 }}</ref><ref name="pmid16713924">{{cite journal | vauthors = de Lau LM, Breteler MM | title = Epidemiology of Parkinson's disease | journal = The Lancet. Neurology | volume = 5 | issue = 6 | pages = 525–35 | date = June 2006 | pmid = 16713924 | doi = 10.1016/S1474-4422(06)70471-9 | s2cid = 39310242 }}</ref><ref name="pmid23225012">{{cite book | vauthors = Mhyre TR, Boyd JT, Hamill RW, Maguire-Zeiss KA | title = Parkinson's disease | volume = 65 | pages = 389–455 | date = 2012 | pmid = 23225012 | pmc = 4372387 | doi = 10.1007/978-94-007-5416-4_16 | series = Subcellular Biochemistry | isbn = 978-94-007-5415-7 }}</ref> The ] is about 0.3% in industrialized countries. PD is more common in the elderly and rates rise from 1% in those over 60 years of age to 4% of the population over 80.<ref name="pmid16713924"/> The mean age of onset is around 60 years, although 5–10% of cases, classified as young onset PD, begin between the ages of 20 and 50.<ref name="pmid15172778"/> Males are more often affected than females at a ratio of around 3:2.<ref name=Lancet2015/> PD may be less prevalent in those of African and Asian ancestry, although this finding is disputed.<ref name="pmid16713924"/> Some studies have proposed that it is more common in men than women, but others failed to detect any differences between the two sexes.<ref name="pmid16713924"/> The ] of PD is between 8 and 18 per 100,000 person–years.<ref name="pmid16713924"/> The age adjusted rate of Parkinson's disease in Estonia is 28.0/100,000 person years.<ref name=Kad2019>{{cite journal | vauthors = Kadastik-Eerme L, Taba N, Asser T, Taba P | title = Incidence and Mortality of Parkinson's Disease in Estonia | journal = Neuroepidemiology | volume = 53 | issue = 1–2 | pages = 63–72 | date = 16 April 2019 | pmid = 30991384 | doi = 10.1159/000499756 | s2cid = 119103425 }}</ref> The Estonian rate has been stable between 2000 and 2019.<ref name=Kad2019/>


==History== ==History==
{{Main|History of Parkinson's disease}} {{Main|History of Parkinson's disease}}
{{Multiple image
], who made important contributions to the understanding of the disease and proposed its current name honoring ]]]
| align = left
Several early sources, including an ] ], an ] medical treatise, the ], and ]'s writings, describe symptoms resembling those of PD.<ref name="pmid15568171">{{cite journal |url=https://www.researchgate.net/publication/8159672| vauthors = García Ruiz PJ | title = Prehistoria de la enfermedad de Parkinson| language = es | journal = Neurologia | volume = 19 | issue = 10 | pages = 735–37 | date = December 2004 | pmid = 15568171 | trans-title = Prehistory of Parkinson's disease}}. The article mistakenly refers to Job 34:19 instead of Job 33:19.</ref> After Galen there are no references unambiguously related to PD until the 17th century.<ref name="pmid15568171" /> In the 17th and 18th centuries, several authors wrote about elements of the disease, including ], ], ] and ].<ref name="pmid15568171" /><ref name="pmid19892136">{{cite book | vauthors = Lanska DJ | title = Chapter 33: the history of movement disorders | volume = 95 | pages = 501–46 | year = 2010 | pmid = 19892136 | doi = 10.1016/S0072-9752(08)02133-7 | isbn = 978-0444520098 | series = Handbook of Clinical Neurology }}</ref><ref name="pmid9380070">{{cite journal | vauthors = Koehler PJ, Keyser A | title = Tremor in Latin texts of Dutch physicians: 16th-18th centuries | journal = Movement Disorders | volume = 12 | issue = 5 | pages = 798–806 | date = September 1997 | pmid = 9380070 | doi = 10.1002/mds.870120531 | s2cid = 310819 }}</ref>
| total_width = 360
| image1 = Jean-Martin Charcot.jpg
| alt1 =
| image2 = Photographs of a Parkinson patient Pierre D.jpg
| alt2 =
| footer = In 1877, ] (left) named the disease for ], credited as the first to comprehensively describe it. Patient Pierre D. (right) served as the model for ]' widely distributed illustration of Parkinson's disease.{{Sfn|Lewis|Plun-Favreau|Rowley|Spillane|2020|p=389}}}}
In 1817, English physician ] published the first full medical description of the disease as a neurological syndrome in his monograph ''An Essay on the Shaking Palsy''.{{Sfn|Goetz|2011|pp=1–2}}{{Sfn|Lees|2007|p=S327}} He presented six clinical cases, including three he had observed on the streets near ] in ].{{Sfn|Goetz|2011|p=2}} Parkinson described three cardinal symptoms: tremor, postural instability and "paralysis" (undistinguished from rigidity or bradykinesia), and speculated that the disease was caused by trauma to the ].{{Sfn|Louis|1997|p=1069}}{{Sfn|Lees|2007|p=S328}}


There was little discussion or investigation of the "shaking palsy" until 1861, when Frenchman ]—regarded as the father of ]—began expanding Parkinson's description, adding bradykinesia as one of the four cardinal symptoms.{{Sfn|Louis|1997|p=1069}}{{Sfn|Goetz|2011|p=2}}{{Sfn|Lees|2007|p=S328}} In 1877, Charcot renamed the disease after Parkinson, as not all patients displayed the tremor suggested by "shaking palsy".{{Sfn|Goetz|2011|p=2}}{{Sfn|Lees|2007|p=S328}} Subsequent neurologists who made early advances to the understanding of Parkinson's include ], ], ], and ].{{Sfn|Lees|2007|p=S329}}
In 1817 an English doctor, ], published his essay reporting six cases of paralysis agitans.<ref name="pmid18175393"/> ''An Essay on the Shaking Palsy'' described the characteristic resting tremor, abnormal posture and gait, paralysis and diminished muscle strength, and the way that the disease progresses over time.<ref name=ParkinsonJEssay/><ref name="pmid9399240">{{cite journal | vauthors = Louis ED | title = The shaking palsy, the first forty-five years: a journey through the British literature | journal = Movement Disorders | volume = 12 | issue = 6 | pages = 1068–72 | date = November 1997 | pmid = 9399240 | doi = 10.1002/mds.870120638 | s2cid = 34630080 }}</ref> Early neurologists who made further additions to the knowledge of the disease include ], ], ] and ], and most notably ], whose studies between 1868 and 1881 were a landmark in the understanding of the disease.<ref name="pmid18175393"/> Among other advances, he made the distinction between rigidity, weakness and bradykinesia.<ref name="pmid18175393"/> He also championed the renaming of the disease in honor of James Parkinson.<ref name="pmid18175393"/>
] (pictured), details a disease with strikingly parkinsonian symptoms.]]
Although Parkinson is typically credited with the first detailed description of PD, many previous texts reference some of the disease's clinical signs.{{Sfn|Bereczki|2010|p=290}} In his essay, Parkinson himself acknowledged partial descriptions by ], ], ], and others.{{Sfn|Lees|2007|p=S328}} Possible earlier but incomplete descriptions include a ] Egyptian ], the ] text '']'', ], and a discussion of tremors by ].{{Sfn|Lees|2007|p=S328}}{{Sfn|Blonder|2018|pp=3–4}} Multiple ] texts may include references to PD, including a discussion in the ]'s Internal Classic ({{Circa|425–221 BC}}) of a disease with symptoms of tremor, stiffness, staring, and stooped posture.{{Sfn|Blonder|2018|pp=3–4}} In 2009, a systematic description of PD was found in the Hungarian medical text ''Pax corporis'' written by Ferenc Pápai Páriz in 1690, some 120 years before Parkinson. Although Páriz correctly described all four cardinal signs, it was only published in Hungarian and was not widely distributed.{{Sfn|Bereczki|2010|pp=290–293}}{{Sfn|Blonder|2018|p=3}}


In 1912 ] described microscopic particles in affected brains, later named "]".<ref name="pmid18175393"/> In 1919 ] reported that the substantia nigra was the main cerebral structure affected, but this finding was not widely accepted until it was confirmed by further studies published by ] in 1938.<ref name="pmid18175393"/> The underlying ] changes in the ] were identified in the 1950s, due largely to the work of ] on the neurotransmitter dopamine and ] on its role on PD.<ref name="pmid18781671" /> In 1997, alpha-synuclein was found to be the main component of Lewy bodies by ], ], ] and others.<ref name="pmid20563819"/> In 1912, ] described microscopic particles in affected brains, later named Lewy bodies.{{Sfn|Sousa-Santos|Pozzobon|Teixeira|2024|pp=1–2}} In 1919, ] reported that the substantia nigra was the main brain structure affected, corroborated by ] in 1938.{{Sfn|Lees|2007|p=S331}} The underlying changes in dopamine signaling were identified in the 1950s, largely by ] and ].{{Sfn|Fahn|2008|p=S500—S501, S504–S505}} In 1997, Polymeropoulos and colleagues at the ] discovered the first gene for PD,{{sfn|Polymeropoulos|Lavedan|Leroy|Ide|1997}} ''SNCA'', which encodes alpha-synuclein. Alpha-synuclein was in turn found to be the main component of Lewy bodies by ], ], ], and others.{{Sfn|Schulz-Schaeffer|2010|p=131}} Anticholinergics and surgery were the only treatments until the use of levodopa,{{Sfn|Lanska|2010|p=507}}{{Sfn|Guridi|Lozano|1997|pp=1180–1183}} which, although first synthesized by ] in 1911,{{Sfn|Fahn|2008|p=S497}} did not enter clinical use until 1967.{{Sfn|Fahn|2008|p=S501}} By the late 1980s, deep brain stimulation introduced by ] and colleagues at ], France, emerged as an additional treatment.{{Sfn|Coffey|2009|pp=209–210}}

Anticholinergics and surgery (lesioning of the ] or some of the basal ganglia structures) were the only treatments until the arrival of levodopa, which reduced their use dramatically.<ref name="pmid19892136" /><ref name="pmid9361073">{{cite journal | vauthors = Guridi J, Lozano AM | title = A brief history of pallidotomy | journal = Neurosurgery | volume = 41 | issue = 5 | pages = 1169–80; discussion 1180–83 | date = November 1997 | pmid = 9361073 | doi = 10.1097/00006123-199711000-00029 }}</ref> ] was first synthesized in 1911 by ], but it received little attention until the mid 20th century.<ref name="pmid18781671" /> It entered clinical practice in 1967 and brought about a revolution in the management of PD.<ref name="pmid18781671">{{cite journal | vauthors = Fahn S | title = The history of dopamine and levodopa in the treatment of Parkinson's disease | journal = Movement Disorders | volume = 23 Suppl 3 | issue = Suppl 3 | pages = S497–508 | year = 2008 | pmid = 18781671 | doi = 10.1002/mds.22028 | s2cid = 45572523 }}</ref><ref>{{cite journal | vauthors = Hornykiewicz O | title = L-DOPA: from a biologically inactive amino acid to a successful therapeutic agent | journal = Amino Acids | volume = 23 | issue = 1–3 | pages = 65–70 | year = 2002 | pmid = 12373520 | doi = 10.1007/s00726-001-0111-9 | s2cid = 25117208 }}</ref> By the late 1980s ] introduced by ] and colleagues at ], France, emerged as a possible treatment.<ref name="pmid18684199">{{cite journal | vauthors = Coffey RJ | title = Deep brain stimulation devices: a brief technical history and review | journal = Artificial Organs | volume = 33 | issue = 3 | pages = 208–20 | date = March 2009 | pmid = 18684199 | doi = 10.1111/j.1525-1594.2008.00620.x }}</ref>


==Society and culture== ==Society and culture==
]—as depicted here by French anatomist ] in 1888—can harm social well-being.]]
===Social impact===
For some people with PD, masked facial expressions and difficulty moderating facial expressions of emotion or recognizing other people's facial expressions can impact social well-being.{{sfn|Prenger|Madray|Van Hedger|Anello|2020|p=2}} As the condition progresses, tremor, other motor symptoms, difficulty communicating, or mobility issues may interfere with social engagement, causing individuals with PD to feel isolated.{{sfn|Crooks|Carter|Wilson|Wynne|2023|p=2,7}} Public perception and awareness of PD symptoms such as shaking, hallucinating, slurring speech, and being off balance is lacking in some countries and can lead to stigma.{{sfn|Crooks|Carter|Wilson|Wynne|2023|p=2}}


===Cost=== ===Cost===
The economic cost of Parkinson's to both individuals and society is high.{{sfn|Schiess|Cataldi|Okun|Fothergill-Misbah|2022|p=931}} Globally, most government health insurance plans do not cover Parkinson's therapies, requiring patients to pay out-of-pocket.{{sfn|Schiess|Cataldi|Okun|Fothergill-Misbah|2022|p=931}} Indirect costs include lifetime earnings losses due to premature death, productivity losses, and caregiver burdens.{{sfn|Yang|Hamilton|Kopil|Beck|2020|p=1}} The duration and progessive nature of PD can place a heavy burden on caregivers:{{sfn|Schiess|Cataldi|Okun|Fothergill-Misbah|2022|p=933}} family members like spouses dedicate around 22 hours per week to care.{{sfn|Yang|Hamilton|Kopil|Beck|2020|p=1}}
{{update|date=August 2020}}

]
In 2010, the total economic burden of Parkinson's across Europe, including indirect and direct medical costs, was estimated to be €13.9 billion (US $14.9 billion) in 2010.{{sfn|Schiess|Cataldi|Okun|Fothergill-Misbah|2022|p=929}} The total burden in the United States was estimated to be $51.9&nbsp;billion in 2017, and is project to surpass $79&nbsp;billion by 2037.{{sfn|Yang|Hamilton|Kopil|Beck|2020|p=1}} However, as of 2022, no rigorous economic surveys had been performed for low or middle income nations.{{sfn|Schiess|Cataldi|Okun|Fothergill-Misbah|2022|p=930}} Regardless, preventative care has been identified as crucial to prevent the rapidly increasing incidence of Parkinson's from overwhelming national health systems.{{sfn|Schiess|Cataldi|Okun|Fothergill-Misbah|2022|p=933}}
The costs of PD to society are high, but precise calculations are difficult due to methodological issues in research and differences between countries.<ref name="pmid17702630">{{cite journal | vauthors = Findley LJ | title = The economic impact of Parkinson's disease | journal = Parkinsonism & Related Disorders | volume = 13 Suppl | issue = Suppl | pages = S8–12 | date = September 2007 | pmid = 17702630 | doi = 10.1016/j.parkreldis.2007.06.003 }}</ref> The annual cost in the UK is estimated to be between £49 million and £3.3 billion, while the cost per affected person per year in the U.S. is probably around $10,000 and the total burden around $23 billion.<ref name="pmid17702630" /> The largest share of direct cost comes from ] and nursing homes, while the share coming from medication is substantially lower.<ref name="pmid17702630" /> Indirect costs are high, due to reduced productivity and the burden on caregivers.<ref name="pmid17702630" /> In addition to economic costs, PD reduces ] of those with the disease and their caregivers.<ref name="pmid17702630" />


===Advocacy=== ===Advocacy===
] signs a pledge from the ]]]
The birthday of James Parkinson, 11 April, has been designated as World Parkinson's Day.<ref name="pmid18175393"/> A red tulip was chosen by international organizations as the symbol of the disease in 2005: it represents the James Parkinson Tulip ], registered in 1981 by a Dutch horticulturalist.<ref name="tulip">{{cite web|url=http://www.gsk.com/infocus/parkinsons.htm|title=Parkinson's – 'the shaking palsy'|date=1 April 2009|publisher=GlaxoSmithKline|url-status=dead|archive-url=https://web.archive.org/web/20110514151652/http://www.gsk.com/infocus/parkinsons.htm|archive-date=14 May 2011}}</ref> Advocacy organizations include the ], which has provided more than $180 million in care, research and support services since 1982,<ref name="urlNational Parkinson Foundation – Mission">{{cite web|url=http://www.parkinson.org/About-Us/Mission|title=National Parkinson Foundation – Mission|access-date=28 March 2011|url-status=dead|archive-url=https://web.archive.org/web/20101221103201/http://parkinson.org/About-Us/Mission|archive-date=21 December 2010}}</ref> ], which has distributed more than $115 million for research and nearly $50 million for education and advocacy programs since its founding in 1957 by William Black;<ref>{{cite journal|journal=Time|url=http://www.time.com/time/magazine/article/0,9171,828597,00.html|title=Education: Joy in Giving|date=18 January 1960|access-date=2 April 2011|url-status=live|archive-url=https://web.archive.org/web/20110220012106/http://www.time.com/time/magazine/article/0,9171,828597,00.html|archive-date=20 February 2011}}</ref><ref>{{cite web|url=http://www.pdf.org/en/about_pdf|title=About PDF|publisher=Parkinson's Disease Foundation|access-date=24 July 2016|url-status=dead|archive-url=https://web.archive.org/web/20110515204903/http://www.pdf.org/en/about_pdf|archive-date=15 May 2011}}</ref> the ], founded in 1961;<ref>{{cite web|url=http://www.apdaparkinson.org/userND/index.asp|title=American Parkinson Disease Association: Home|publisher=American Parkinson Disease Association|access-date=9 August 2010|url-status=dead|archive-url=https://web.archive.org/web/20120510165933/http://www.apdaparkinson.org/userND/index.asp|archive-date=10 May 2012}}</ref> and the ], founded in 1992.<ref>{{cite web|url=http://www.epda.eu.com/about-us/|title=About EPDA|year=2010|publisher=European Parkinson's Disease Association|access-date=9 August 2010|url-status=live|archive-url=https://web.archive.org/web/20100815232300/http://www.epda.eu.com/about-us/|archive-date=15 August 2010}}</ref>
The birthday of James Parkinson, 11 April, has been designated as World Parkinson's Day.<ref name="pmid18175393">{{Harvnb|Lees|2007|pages=S327–S334}}</ref> A red tulip was chosen by international organizations as the symbol of the disease in 2005; it represents the 'James Parkinson' tulip ], registered in 1981 by a Dutch horticulturalist.{{sfn|GlaxoSmithKline}}

Advocacy organizations include the ], which has provided more than $180&nbsp;million in care, research, and support services since 1982,{{sfn|National Parkinson Foundation}} ], which has distributed more than $115&nbsp;million for research and nearly $50&nbsp;million for education and advocacy programs since its founding in 1957 by William Black;{{sfn|Time 1960}}{{sfn|Parkinson's Disease Foundation}} the ], founded in 1961;{{sfn|American Parkinson Disease Association}} and the European Parkinson's Disease Association, founded in 1992.{{sfn|European Parkinson's Disease Association}}


===Notable cases=== ===Notable cases===
{{Main|List of people diagnosed with Parkinson's disease}} {{Main|List of people diagnosed with Parkinson's disease}}
] at the ] in ], at the age of 64. He had shown signs of parkinsonism from the age of 38 until his death.]] ] and boxer ] (center) are pictured in 2002 speaking before the ] to urge increased funding for Parkinson's research.]]
In the 21st century, the diagnosis of Parkinson's among notable figures has increased the public's understanding of the disorder.{{sfn|Parkinson's Foundation}} Actor ] was diagnosed with PD at 29 years old,{{sfn|The Michael J. Fox Foundation for Parkinson's Research}} and has used his diagnosis to increase awareness of the disease.{{sfn|Davis|2007}} To illustrate the effects of the disease, Fox has appeared without medication in television roles and before the ] without medication.{{sfn|Brockes|2009}} ], which he founded in 2000, has raised over $2 billion for Parkinson's research.{{sfn|Burleson|Breen|2023}}
<!--


Boxer ] showed signs of PD when he was 38, but was undiagnosed until he was 42, and has been called the "world's most famous Parkinson's patient".
Parkinson's is a common disease, so lots of notable people have it. Please only add people here who have played a MAJOR role in supporting research or public understanding of the disease. All others can be listed at the main article about people diagnosed with Parkinson's disease.
{{sfn|Brey|2006}} Whether he had PD or ] is unresolved.{{sfn|Matthews|2006|p=10–23}} Cyclist and Olympic medalist ], diagnosed with Parkinson's at 40, started the ] in 2004 to support PD research.{{sfn|Macur|2008}}{{sfn|Davis Phinney Foundation}}


Several historical figures have been theorized to have had Parkinson's, often framed in the industriousness and inflexibility of the so-called "Parkinsonian personality".{{sfn|Luca|Nicoletti|Mostile|Zappia|2018|pp=1–2}} For instance, English philosopher ] was diagnosed with "shaking palsy"—assumed to have been Parkinson's—but continued writing works such as '']''.{{sfn|McCrum|2017}}{{sfn|Kinsley|2014}}{{sfn|Raudino|2011|pp=945–949}} ] is widely believed to have had Parkinson's, and the condition may have influenced his decision making.{{sfn|Gupta|Kim|Agarwal|Lieber|2015|pp=1447–1452}}{{sfn|Boettcher|Bonney|Smitherman|Sughrue|2015|p=E8}}{{sfn|Lieberman|1996|p=95}} ] was also reported to have died from the disorder.{{sfn|Glass|2016}}
-->Actor ] has PD and has greatly increased the public awareness of the disease.<ref name="MJF_TIME"/> After diagnosis, Fox embraced his Parkinson's in television roles, sometimes acting without medication, in order to further illustrate the effects of the condition. He has written two autobiographies in which his fight against the disease plays a major role,<ref name="MJF_guardian">{{cite news|url=https://www.theguardian.com/lifeandstyle/2009/apr/11/michael-j-fox-parkinsons|title='It's the gift that keeps on taking'|date=11 April 2009| vauthors = Brockes E |work=The Guardian|access-date=25 October 2010|url-status=live|archive-url=https://web.archive.org/web/20131008000425/http://www.theguardian.com/lifeandstyle/2009/apr/11/michael-j-fox-parkinsons|archive-date=8 October 2013}}</ref> and appeared before the ] without medication to illustrate the effects of the disease.<ref name="MJF_guardian" /> ] aims to develop a cure for Parkinson's disease.<ref name="MJF_guardian" /> Fox received an ] in medicine from ] for his contributions to research in Parkinson's disease.<ref name="doctorate_Fox">{{cite news|url=http://ki.se/ki/jsp/polopoly.jsp?d=25844&a=96573&l=en&newsdep=25844|title=Michael J. Fox to be made honorary doctor at Karolinska Institutet|date=5 March 2010|publisher=Karolinska Institutet|access-date=2 April 2011|url-status=dead|archive-url=https://web.archive.org/web/20110930040553/http://ki.se/ki/jsp/polopoly.jsp?d=25844&a=96573&l=en&newsdep=25844|archive-date=30 September 2011}}</ref>


==Clinical research==
Professional cyclist and Olympic medalist ], who was diagnosed with young onset Parkinson's at age 40, started the ] in 2004 to support Parkinson's research, focusing on quality of life for people with the disease.<ref name=Mac2008/><ref name="DPF">{{cite web|url=http://davisphinneyfoundation.org/dpf/who-we-are/|title=Who We Are|publisher=Davis Phinney Foundation|access-date=18 January 2012|url-status=live|archive-url=https://web.archive.org/web/20120111054225/http://davisphinneyfoundation.org/dpf/who-we-are/|archive-date=11 January 2012}}</ref>
{{Main|Research in Parkinson's disease}}
] conducts Parkinson's research aboard the ] in 2018]]
As of 2024, no disease-modifying therapies exist that reverse or slow the progression of Parkinson's.{{Sfn|Crotty|Schwarzschild|2020|p=1}}{{Sfn|Fabbri|Rascol|Foltynie|Carroll|2024|p=2}} Active research directions include the search for new ]s of the disease and development and trial of ], ] transplants, and ] agents.{{sfn|Poewe|Seppi|Tanner|Halliday|2017}} Improved treatments will likely combine therapeutic strategies to manage symptoms and enhance outcomes.{{sfn|Pardo-Moreno|García-Morales|Suleiman-Martos|Rivas-Domínguez|2023|p=1}} Reliable ] are needed for early diagnosis, and research criteria for their identification have been established.{{sfn|Li|Le|2020|p=183}}{{sfn|Heinzel|Berg|Gasser|Chen|2019}}


===Neuroprotective treatments===
Boxer ] showed signs of Parkinson's when he was 38, but was not diagnosed until he was 42, and has been called the "World's most famous Parkinson's patient".<ref name="Ali_NN_comment"/> Whether he had PD or ] is unresolved.<ref name="Ali_NN">{{cite journal|title=Ali's Fighting Spirit|date=April 2006|journal=Neurology Now| vauthors= Matthews W |volume=2|issue=2|pages=10–23|doi=10.1097/01222928-200602020-00004|s2cid=181104230}}</ref><ref name="Ali_NYT">{{cite news |url= https://www.nytimes.com/1988/07/17/magazine/ali-still-magic.html |title=Ali: Still Magic |date=17 July 1988 | vauthors = Tauber P |work=The New York Times |access-date=2 April 2011 |url-status=live |archive-url= https://web.archive.org/web/20161117151827/http://www.nytimes.com/1988/07/17/magazine/ali-still-magic.html |archive-date=17 November 2016}}</ref>
{{See also|Anti-α-synuclein drug}}
] that prevent alpha-synuclein oligomerization and aggregation or promote their clearance are under active investigation, and potential therapeutic strategies include ] and ] like ] and ].{{sfn|Pardo-Moreno|García-Morales|Suleiman-Martos|Rivas-Domínguez|2023|pp=12-13}}{{sfn|Alfaidi|Barker|Kuan|2024|p=1}}{{sfn|Jasutkar|Oh|Mouradian|2022|p=208}} While immunotherapies show promise, their effiacy is often inconsistent.{{sfn|Alfaidi|Barker|Kuan|2024|p=1}} Anti-inflammatory drugs that target ] and the ] offer another potential therapeutic approach.{{sfn|Pardo-Moreno|García-Morales|Suleiman-Martos|Rivas-Domínguez|2023|pp=10-11}}


As the ] in PD is often disrupted and produces toxic compounds, ] might restore a healthy microbiome and alleviate various motor and non-motor symptoms.{{sfn|Pardo-Moreno|García-Morales|Suleiman-Martos|Rivas-Domínguez|2023|pp=12-13}} ]—] that enhance the growth, maturation, and survival of neurons—show modest results but require invasive surgical administration. ] may represent a more feasible delivery platform.{{sfn|Pardo-Moreno|García-Morales|Suleiman-Martos|Rivas-Domínguez|2023|p=13}} ] may restore the calcium imbalance present in Parkinson's, and are being investigated as a neuroprotective treatment.{{sfn|Pardo-Moreno|García-Morales|Suleiman-Martos|Rivas-Domínguez|2023|p=10}} Other therapies, like ], may reduce the abnormal accumulation of iron in PD.{{sfn|Pardo-Moreno|García-Morales|Suleiman-Martos|Rivas-Domínguez|2023|p=10}}
==Research==
{{update|date=July 2020}}
{{See also|Parkinson's disease clinical research}}
There are no approved disease modifying drugs (drugs that target the causes or damage) for Parkinson's, this is a major focus of Parkinson's research.<ref name="Poewe2017" /> Active research directions include the search for new ]s of the disease and studies of the potential usefulness of ], ] transplants and ] agents.<ref name="Poewe2017" />


===Animal models=== ===Cell-based therapies===
{{Main|Cell-based therapies for Parkinson's disease}}
PD is not known to occur naturally in any species other than humans, although animal models which show some features of the disease are used in research. The appearance of parkinsonism in a group of drug addicts in the early 1980s who consumed a contaminated batch of the synthetic ] ] led to the discovery of the chemical ] as an agent that causes parkinsonism in non-human primates as well as in humans.<ref name="pmid6823561">{{cite journal | vauthors = Langston JW, Ballard P, Tetrud JW, Irwin I | title = Chronic Parkinsonism in humans due to a product of meperidine-analog synthesis | journal = Science | volume = 219 | issue = 4587 | pages = 979–80 | date = February 1983 | pmid = 6823561 | doi = 10.1126/science.6823561 | bibcode = 1983Sci...219..979L | s2cid = 31966839 | url = https://semanticscholar.org/paper/0fa587e1e8aba5327f1de9237279c47477b9e12d }}</ref> Other predominant toxin-based models employ the insecticide ], the herbicide paraquat and the fungicide ].<ref name="pmid19729209">{{cite journal | vauthors = Cicchetti F, Drouin-Ouellet J, Gross RE | title = Environmental toxins and Parkinson's disease: what have we learned from pesticide-induced animal models? | journal = Trends in Pharmacological Sciences | volume = 30 | issue = 9 | pages = 475–83 | date = September 2009 | pmid = 19729209 | doi = 10.1016/j.tips.2009.06.005 }}</ref> Models based on toxins are most commonly used in ]s. ] rodent models that replicate various aspects of PD have been developed.<ref name="pmid18642640">{{cite book | vauthors = Harvey BK, Wang Y, Hoffer BJ | title = Transgenic rodent models of Parkinson's disease | journal = ] | volume = 101 | pages = 89–92 | year = 2008 | pmid = 18642640 | pmc = 2613245 | doi = 10.1007/978-3-211-78205-7_15 | isbn = 978-3-211-78204-0 | series = Acta Neurochirurgica Supplementum }}</ref> The use of ] ], creates a model of Parkinson's disease in rats by targeting and destroying dopaminergic neurons in the nigrostriatal pathway when injected into the substantia nigra.<ref>{{cite journal | vauthors = Blum D, Torch S, Lambeng N, ''et al'' | title = Molecular pathways involved in the neurotoxicity of 6-OHDA, dopamine and MPTP: contribution to the apoptotic theory in Parkinson's disease | journal = Progress in Neurobiology | volume = 65 | issue = 2 | pages = 135–72 | date = October 2001 | pmid = 11403877 | doi = 10.1016/S0301-0082(01)00003-X | s2cid = 19095092 }}</ref>
{{Multiple image
| align = right
| total_width = 400
| image1 = Parkinson's induced pluripotent stem cell.jpg
| alt1 = Researchers at Argonne National Laboratory examining induced pluripotent stem cells
| image2 = Efficient-Conversion-of-Astrocytes-to-Functional-Midbrain-Dopaminergic-Neurons-Using-a-Single-pone.0028719.s002.ogv
| alt2 = The action potentials of an astrocyte converted into a dopaminergic neuron
| footer = Researchers at ] examine ] (iPSCs) for use in Parkinson's and other diseases: the ] of one such iPSC differentiated into a ] are visible at right.
}}
In contrast to other neurodegenerative disorders, many Parkinson's symptoms can be attributed to the loss of a single cell type. Consequently, dopaminergic neuron regeneration is a promising therapeutic approach.{{Sfn|Parmar|Grealish|Henchcliffe|2020|pp=103}} Although most initial research sought to generate dopaminergic neuron precursor cells from fetal brain tissue,{{Sfn|Parmar|Grealish|Henchcliffe|2020|pp=103-104}} ]—particularly ] (iPSCs)—have become an increasingly popular tissue source.{{Sfn|Parmar|Grealish|Henchcliffe|2020|pp=106}}{{Sfn|Henchcliffe|Parmar|2018|pp=134}}

Both fetal and iPSC-derived DA neurons have been transplanted into patients in clinical trials.{{Sfn|Parmar|Grealish|Henchcliffe|2020|pp=106, 108}}{{sfn|Schweitzer|Song|Herrington|Park|2020|p=1926}} Although some patients see improvements, the results are highly variable. Adverse effects, such as ] arising from excess dopamine release by the transplanted tissues, have also been observed.{{Sfn|Parmar|Grealish|Henchcliffe|2020|pp=105, 109}}{{Sfn|Henchcliffe|Parmar|2018|pp=132}}


===Gene therapy=== ===Gene therapy===
{{Main|Gene therapy in Parkinson's disease}}
Gene therapy typically involves the use of a non-infectious ] (i.e., a ] such as the ]) to shuttle genetic material into a part of the brain. Several approaches have been tried. These approaches have involved the expression of growth factors to try to prevent damage (] – a ]-family growth factor), and enzymes such as glutamic acid decarboxylase (] – the enzyme that produces ]), tyrosine hydroxylase (the enzyme that produces L-DOPA) and ] (COMT – the enzyme that converts L-DOPA to dopamine). There have been no reported safety concerns, but the approaches have largely failed in phase 2 clinical trials.<ref name=Poewe2017>{{Cite journal|vauthors= Poewe W, Seppi K, Tanner CM, ''et al''|date=23 March 2017|title=Parkinson disease |journal=Nature Reviews Disease Primers|language=en|volume=3|issue=1|page=17013|doi=10.1038/nrdp.2017.13|pmid=28332488|s2cid=11605091|issn=2056-676X}}</ref> The delivery of GAD showed promise in phase 2 trials in 2011, but whilst effective at improving motor function was inferior to DBS. Follow-up studies in the same cohort have suggested persistent improvement.<ref>{{cite journal|vauthors=Hitti FL, Yang AI, Gonzalez-Alegre P, Baltuch GH|date=September 2019|title=Human gene therapy approaches for the treatment of Parkinson's disease: An overview of current and completed clinical trials|journal=Parkinsonism Relat. Disord.|volume=66|pages=16–24|doi=10.1016/j.parkreldis.2019.07.018|pmid=31324556}}</ref>
] for Parkinson's seeks to restore the healthy function of dopaminergic neurons in the substantia nigra by delivering genetic material—typically through a viral vector—to these diseased cells.{{sfn|Van Laar|Van Laar|San Sebastian|Merola|2021|p=S174}}{{sfn|Hitti|Yang|Gonzalez-Alegre|Baltuch|2019|p=16}} This material may deilver a functional, ] version of a gene, or ] a pathological variants.{{sfn|Hitti|Yang|Gonzalez-Alegre|Baltuch|2019|pp=16-17}} Experimental gene therapies for PD have aimed to increase the expression of ] or enzymes involved in dopamine synthesis, like ].{{sfn|Van Laar|Van Laar|San Sebastian|Merola|2021|p=S174, S176}} The one-time delivery of genes circumvents the recurrent invasive administration required to administer some peptides and proteins to the brain.{{sfn|Hitti|Yang|Gonzalez-Alegre|Baltuch|2019|p=21}} MicroRNAs are an emerging PD gene therapy platform that may serve as an alternative to viral vectors.{{sfn|Shaheen|Shaheen|Osama|Nashwan|2024|pp=5-6}}


==Notes and references==
===Neuroprotective treatments===
===Notes===
] (chemical structure pictured) have been proposed as neuroprotectors in PD, but their effectiveness has not been proven.]]
{{reflist|group=note}}
Investigations on ] are at the forefront of PD research. Several molecules have been proposed as potential treatments.<ref name="pmid20495568"/> However, none of them have been conclusively demonstrated to reduce degeneration.<ref name="pmid20495568"/> Agents currently under investigation include, ], ]s (], ]), ] (], ]), ]s (]) and ]s (]).<ref name="pmid20495568"/> Reducing ] pathology is a major focus of preclinical research.<ref name="Dimond">{{cite web|url=http://www.genengnews.com/analysis-and-insight/no-new-parkinson-disease-drug-expected-anytime-soon/77899336/|title=No New Parkinson Disease Drug Expected Anytime Soon| vauthors = Dimond PF |date=16 August 2010|work=GEN news highlights|publisher=GEN-Genetic Engineering & Biotechnology News|url-status=live|archive-url=https://web.archive.org/web/20101031023451/http://www.genengnews.com/analysis-and-insight/no-new-parkinson-disease-drug-expected-anytime-soon/77899336/|archive-date=31 October 2010}}</ref> A ] that primes the human immune system to destroy ], PD01A (developed by Austrian company, Affiris), entered clinical trials and a phase 1 report in 2020 suggested safety and tolerability.<ref>{{cite journal | vauthors = Volc D, Poewe W, Kutzelnigg A, ''et al'' | title = Safety and immunogenicity of the α-synuclein active immunotherapeutic PD01A in patients with Parkinson's disease: a randomised, single-blinded, phase 1 trial | journal = The Lancet. Neurology | volume = 19 | issue = 7 | pages = 591–600 | date = July 2020 | pmid = 32562684 | doi = 10.1016/S1474-4422(20)30136-8 | s2cid = 219947651 }}</ref><ref name="NS1">{{cite news |url= https://www.newscientist.com/article/mg21428682.000-worlds-first-parkinsons-vaccine-is-trialled.html |title=World's first Parkinson's vaccine is trialled |date=7 June 2012 |work=New Scientist |url-status=live |archive-url= https://web.archive.org/web/20150423080305/http://www.newscientist.com/article/mg21428682.000-worlds-first-parkinsons-vaccine-is-trialled.html |location= London |archive-date=23 April 2015}}</ref> In 2018, an antibody, PRX002/RG7935, showed preliminary safety evidence in stage I trials supporting continuation to stage II trials.<ref name="JAMA">{{cite journal | vauthors = Jankovic J, Goodman I, Safirstein B, ''et al'' | title = Safety and Tolerability of Multiple Ascending Doses of PRX002/RG7935, an Anti-α-Synuclein Monoclonal Antibody, in Patients With Parkinson Disease: A Randomized Clinical Trial | journal = JAMA Neurology | volume = 75 | issue = 10 | pages = 1206–14 | date = October 2018 | pmid = 29913017 | pmc = 6233845 | doi = 10.1001/jamaneurol.2018.1487 }}</ref>


===Cell-based therapies=== ===Citations===
{{Reflist}}
{{Main|Cell-based therapies for Parkinson's disease}}
Since early in the 1980s, ], ], ] or ]l tissues have been used in ], in which dissociated cells are injected into the substantia nigra in the hope that they will incorporate themselves into the brain in a way that replaces the dopamine-producing cells that have been lost.<ref name="pmid20495568"/> These sources of tissues have been largely replaced by ] derived dopaminergic neurons as this is thought to represent a more feasible source of tissue. There was initial evidence of ] dopamine-producing cell transplants being beneficial, ] to date have not determined whether there is a long-term benefit.<ref name="hench">{{cite journal | vauthors = Henchcliffe C, Parmar M | title = Repairing the Brain: Cell Replacement Using Stem Cell-Based Technologies | journal = Journal of Parkinson's Disease | year = 2018 | volume = 8 | issue = s1 | pages = S131–37 | pmid = 30584166 | pmc = 6311366 | doi = 10.3233/JPD-181488 }}</ref> An additional significant problem was the excess release of dopamine by the transplanted tissue, leading to ].<ref name=hench/> In 2020, a first in human clinical trial reported the transplantation of induced pluripotent stem cells into the brain of a person suffering from Parkinson's disease.<ref>{{cite journal | vauthors = Schweitzer JS, Song B, Herrington TM, ''et al'' | title = Personalized iPSC-Derived Dopamine Progenitor Cells for Parkinson's Disease | journal = The New England Journal of Medicine | volume = 382 | issue = 20 | pages = 1926–32 | date = May 2020 | pmid = 32402162 | pmc = 7288982 | doi = 10.1056/NEJMoa1915872 }}</ref>


===Other=== ===Works cited===
====Books====
] temporarily improves levodopa-induced dyskinesias.<ref name="pmid20714078">{{cite journal | vauthors = Koch G | title = rTMS effects on levodopa induced dyskinesias in Parkinson's disease patients: searching for effective cortical targets | journal = Restorative Neurology and Neuroscience | volume = 28 | issue = 4 | pages = 561–68 | year = 2010 | pmid = 20714078 | doi = 10.3233/RNN-2010-0556 }}</ref> Its usefulness in PD is an open research topic.<ref name="pmid20714064">{{cite journal | vauthors = Platz T, Rothwell JC | title = Brain stimulation and brain repair – rTMS: from animal experiment to clinical trials – what do we know? | journal = Restorative Neurology and Neuroscience | volume = 28 | issue = 4 | pages = 387–98 | year = 2010 | pmid = 20714064 | doi = 10.3233/RNN-2010-0570}}</ref> Several ]s have been proposed as possible treatments; however there is no evidence that ]s or ]s improve symptoms.<ref name="pmid16606908">{{cite journal | vauthors = Suchowersky O, Gronseth G, Perlmutter J, Reich S, Zesiewicz T, Weiner WJ | title = Practice Parameter: neuroprotective strategies and alternative therapies for Parkinson disease (an evidence-based review): report of the Quality Standards Subcommittee of the American Academy of Neurology | journal = Neurology | volume = 66 | issue = 7 | pages = 976–82 | date = April 2006 | pmid = 16606908 | doi = 10.1212/01.wnl.0000206363.57955.1b | doi-access = free }}</ref> There is no evidence to substantiate that ] and practice of ], or ], have any effect on the course of the disease or symptoms.<ref name="pmid18374620">{{cite journal | vauthors = Lee MS, Lam P, Ernst E | title = Effectiveness of tai chi for Parkinson's disease: a critical review | journal = Parkinsonism & Related Disorders | volume = 14 | issue = 8 | pages = 589–94 | date = December 2008 | pmid = 18374620 | doi = 10.1016/j.parkreldis.2008.02.003 }}</ref><ref name="pmid18973253">{{cite journal | vauthors = Lee MS, Ernst E | title = Qigong for movement disorders: A systematic review | journal = Movement Disorders | volume = 24 | issue = 2 | pages = 301–03 | date = January 2009 | pmid = 18973253 | doi = 10.1002/mds.22275 | s2cid = 206239252 }}</ref><ref name="pmid18618661">{{cite journal | vauthors = Lee MS, Shin BC, Kong JC, Ernst E | title = Effectiveness of acupuncture for Parkinson's disease: a systematic review | journal = Movement Disorders | volume = 23 | issue = 11 | pages = 1505–15 | date = August 2008 | pmid = 18618661 | doi = 10.1002/mds.21993 | s2cid = 24713983 | url = https://semanticscholar.org/paper/b99f5e8de469d13d5a065bcd34f0d3da68d6e34e }}</ref>
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{{Refend}}


====Journal articles====
The role of the ] and the ] in Parkinsons became a topic of study in the 2010s, starting with work in germ-free transgenic mice, in which ]s from people with PD had worse outcomes. Some studies in humans have shown a correlation between patterns of ] in the gut flora in the people with PD, and these patterns, along with a measure of severity of constipation, could diagnose PD with a 90% specificity but only a 67% sensitivity. As of 2017 some scientists hypothesized that changes in the gut flora might be an early site of PD pathology, or might be part of the pathology.<ref>{{cite journal | vauthors = Tremlett H, Bauer KC, Appel-Cresswell S, Finlay BB, Waubant E | title = The gut microbiome in human neurological disease: A review | journal = Annals of Neurology | volume = 81 | issue = 3 | pages = 369–82 | date = March 2017 | pmid = 28220542 | doi = 10.1002/ana.24901 | s2cid = 25394413 }}</ref><ref>{{cite book | vauthors = Klingelhoefer L, Reichmann H | title = Nonmotor Parkinson's: The Hidden Face – Management and the Hidden Face of Related Disorders | chapter = The Gut and Nonmotor Symptoms in Parkinson's Disease | journal = International Review of Neurobiology | volume = 134 | pages = 787–809 | date = 2017 | pmid = 28805583 | doi = 10.1016/bs.irn.2017.05.027 | isbn = 978-0128126035 }}</ref> Evidence indicates that gut microbiota can produce ] that interferes with the normal function of α-synuclein.<ref>{{cite journal|last1=Bhattacharyya|first1=Dipita|last2=Mohite|first2=Ganesh M.|last3=Krishnamoorthy|first3=Janarthanan|last4=Gayen|first4=Nilanjan|last5=Mehra|first5=Surabhi|last6=Navalkar|first6=Ambuja|last7=Kotler|first7=Samuel A.|last8=Ratha|first8=Bhisma N.|last9=Ghosh|first9=Anirban|last10=Kumar|first10=Rakesh|last11=Garai|first11=Kanchan|last12=Mandal|first12=Atin K.|last13=Maji|first13=Samir K.|last14=Bhunia|first14=Anirban|title=Lipopolysaccharide from Gut Microbiota Modulates α-Synuclein Aggregation and Alters Its Biological Function|journal=ACS Chemical Neuroscience|volume=10|issue=5|year=2019|pages=2229–2236|issn=1948-7193|doi=10.1021/acschemneuro.8b00733|pmid=30855940}}</ref>
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* {{Cite journal |vauthors=Blauwendraat C, Nalls MA, Singleton AB |date=February 2020 |title=The genetic architecture of Parkinson's disease |journal=The Lancet. Neurology |volume=19 |issue=2 |pages=170–178 |doi=10.1016/S1474-4422(19)30287-X |pmc=8972299 |pmid=31521533}}
* {{Cite journal |vauthors=Winiker K, Kertscher B |date=2023 |title=Behavioural interventions for swallowing in subjects with Parkinson's disease: A mixed methods systematic review |journal=International Journal of Language & Communication Disorders |volume=58 |issue=4 |pages=1375–1404 |doi=10.1111/1460-6984.12865 |pmid=36951546 |ref=none |doi-access=free}}
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Ventures have been undertaken to explore antagonists of ]s (specifically ]) as an avenue for novel drugs for Parkinson's.<ref>{{Cite journal|vauthors= Jenner P|date=2014|title=An overview of adenosine A2A receptor antagonists in Parkinson's disease|journal=International Review of Neurobiology|volume=119|pages=71–86|doi=10.1016/B978-0-12-801022-8.00003-9|issn=2162-5514|pmid=25175961|isbn=978-0128010228}}</ref> Of these, ] has emerged as the most successful medication and was approved for medical use in the United States in 2019.<ref name=FDA2020>{{Cite web|url=http://www.fda.gov/news-events/press-announcements/fda-approves-new-add-drug-treat-episodes-adults-parkinsons-disease|title=FDA approves new add-on drug to treat off episodes in adults with Parkinson's disease | author = Office of the Commissioner |date=20 February 2020|website=FDA|language=en|access-date=23 February 2020}}</ref> It is approved as an add-on treatment to the levodopa/carbidopa regime.<ref name=FDA2020/>
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* {{Cite journal|vauthors=Tolosa E, Garrido A, Scholz SW, Poewe W|date=May 2022|title=Challenges in the diagnosis of Parkinson's disease|journal=Lancet Neurology|volume=20|issue=5|pages=385–397|doi=10.1016/S1474-4422(21)00030-2 |pmid=33894193|pmc=8185633}}
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* {{Cite journal|vauthors=Ugrumov M|date=June 2020|title=Development of early diagnosis of Parkinson's disease: Illusion or reality?|journal=CNS Neuroscience and Therapeutics|volume=26|issue=10|pages=997–1009|doi=10.1111/cns.13429 |pmid=32597012|pmc=7539842}}
* {{Cite journal|vauthors=Rizzo G, Copetti M, Arcuti S, Martino D, Fontana A, Logroscino G|date=February 2016|title=Accuracy of clinical diagnosis of Parkinson disease: A systematic review and meta-analysis|journal=Neurology|volume=86|issue=6|pages=566–576|doi=10.1212/WNL.0000000000002350 |pmid=26764028}}
* {{Cite journal|vauthors=Bidesi NS, Andersen IV, Windhorst AD, Shalgunov V, Herth MM|date=November 2021|title=The role of neuroimaging in Parkinson's disease|journal=Journal of Neurochemistry|volume=159|issue=4|pages=660–689|doi=10.1111/jnc.15516 |pmid=34532856|pmc=9291628}}
*{{Cite journal |vauthors=Brooks DJ |date=April 2010 |title=Imaging approaches to Parkinson disease |journal=Journal of Nuclear Medicine |volume=51 |issue=4 |pages=596–609 |doi=10.2967/jnumed.108.059998 |pmid=20351351}}
*{{Cite journal |vauthors=Suwijn SR, van Boheemen CJ, de Haan RJ, Tissingh G, Booij J, de Bie RM |date=2015 |title=The diagnostic accuracy of dopamine transporter SPECT imaging to detect nigrostriatal cell loss in patients with Parkinson's disease or clinically uncertain parkinsonism: a systematic review |journal=EJNMMI Research |volume=5 |pages=12 |doi=10.1186/s13550-015-0087-1 |pmc=4385258 |pmid=25853018 |doi-access=free}}
*{{Cite journal|vauthors=Caproni S, Colosimo C|date=February 2020|title=Diagnosis and Differential Diagnosis of Parkinson Disease|journal=Clinical Geriatric Medicine|volume=36|pages=13–24|doi=10.1016/j.cger.2019.09.014 |pmid=31733693}}
*{{Cite journal|vauthors=Lieberman A|date=April 1996|title=Adolf Hitler had post-encephalitic Parkinsonism|journal=Parkinsonism & Related Disorders|volume=2|issue=2|pages=95-103|pmid=18591024}}
{{Refend}}


== References == ====Web sources====
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*{{Cite web |title=About PDF |url=http://www.pdf.org/en/about_pdf |archive-url=https://web.archive.org/web/20110515204903/http://www.pdf.org/en/about_pdf |archive-date=15 May 2011 |access-date=24 July 2016 |publisher=Parkinson's Disease Foundation|ref={{Harvid|Parkinson's Disease Foundation}}}}
*{{Cite web |title=American Parkinson Disease Association: Home |url=http://www.apdaparkinson.org/userND/index.asp |archive-url=https://web.archive.org/web/20120510165933/http://www.apdaparkinson.org/userND/index.asp |archive-date=10 May 2012 |access-date=9 August 2010 |publisher=American Parkinson Disease Association|ref={{Harvid|American Parkinson Disease Association}}}}
*{{cite news | vauthors = Macur J |title=For the Phinney Family, a Dream and a Challenge |url= https://www.nytimes.com/2008/03/26/sports/othersports/26cycling.html |newspaper=The New York Times |access-date=25 May 2013 |date=26 March 2008 |quote=About 1.5 million Americans have received a diagnosis of Parkinson's disease, but only 5 to 10 percent learn of it before age 40, according to the National Parkinson Foundation. Davis Phinney was among the few. |url-status=live |archive-url= https://web.archive.org/web/20141106025145/http://www.nytimes.com/2008/03/26/sports/othersports/26cycling.html |archive-date=6 November 2014}}
*{{cite web |title=Michael's Story |url=https://www.michaeljfox.org/michaels-story |website=The Michael J. Fox Foundation for Parkinson's Research |access-date=7 May 2023|ref={{Harvid|The Michael J. Fox Foundation for Parkinson's Research}}}}
*{{Cite web |title=National Parkinson Foundation – Mission |url=http://www.parkinson.org/About-Us/Mission |archive-url=https://web.archive.org/web/20101221103201/http://parkinson.org/About-Us/Mission |archive-date=21 December 2010 |access-date=28 March 2011|ref={{Harvid|National Parkinson Foundation}}}}
*{{cite web|url=https://www.parkinson.org/understanding-parkinsons/statistics/notable-figures|title=Notable Figures with Parkinson's|publisher=Parkinson's Foundation|access-date=22 November 2023|ref={{Harvid|Parkinson's Foundation}}}}
* {{Wikicite|reference ={{Cite web |title=Parkinson's Disease |url=https://www.ninds.nih.gov/health-information/disorders/parkinsons-disease#:~:text=Parkinson's%20disease%20(PD)%20is%20movement,the%20body%2C%20or%20impaired%20balance. |access-date=2 September 2024 |publisher=National Institute of Neurological Disorders and Stroke}}|ref={{Harvid|National Institute of Neurological Disorders and Stroke}}}}
*{{Cite web |date=1 April 2009 |title=Parkinson's – 'the shaking palsy' |url=http://www.gsk.com/infocus/parkinsons.htm |archive-url=https://web.archive.org/web/20110514151652/http://www.gsk.com/infocus/parkinsons.htm |archive-date=14 May 2011 |publisher=GlaxoSmithKline|ref={{Harvid|GlaxoSmithKline}}}}
* {{Wikicite|reference ={{Cite web |title=Symptoms of PD |url=https://med.stanford.edu/parkinsons/symptoms-PD.html |access-date=2 September 2024 |website=Stanford Parkinson's Community Outreach |publisher=Stanford University School Medicine}}|ref={{Harvid|Stanford University School Medicine}}}}
*{{cite web|url=http://davisphinneyfoundation.org/dpf/who-we-are/|title=Who We Are|publisher=Davis Phinney Foundation|access-date=18 January 2012|url-status=live|archive-url=https://web.archive.org/web/20120111054225/http://davisphinneyfoundation.org/dpf/who-we-are/|archive-date=11 January 2012|ref={{Harvid|Davis Phinney Foundation}}}}

{{Refend}}

====News publications====
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*{{cite news|last1=Burleson|first1=Nate|last2=Breen|first2=Kerry|date=9 November 2023|title=Michael J. Fox talks funding breakthrough research for Parkinson's disease|url=https://www.cbsnews.com/news/michael-j-fox-parkinsons-research-funded-by-his-foundation/|work=CBS News|access-date=23 November 2023}}
*{{cite news|last=Glass|first=Andrew|date=9 September 2016|title=Mao Zedong dies in Beijing at age 82, Sept. 9, 1976|url=https://www.politico.com/story/2016/09/mao-zedong-dies-in-beijing-at-age-82-sept-9-1976-227742|work=Politico|access-date=30 October 2023}}
*{{cite news|url= https://www.nytimes.com/1988/07/17/magazine/ali-still-magic.html|title=Ali: Still Magic|date=17 July 1988|vauthors=Tauber P |work=The New York Times|access-date=2 April 2011|url-status=live|archive-url= https://web.archive.org/web/20161117151827/http://www.nytimes.com/1988/07/17/magazine/ali-still-magic.html|archive-date=17 November 2016}}
*{{cite news|last=McCrum|first=Robert|date=20 November 2017|title=The 100 best nonfiction books: No 94 – Leviathan by Thomas Hobbes (1651)|url=https://www.theguardian.com/books/2017/nov/20/the-100-best-nonfiction-books-no-94-leviathan-thomas-hobbes-1651|work=The Guardian|access-date=23 November 2023}}
*{{cite magazine|last=Kinsley|first=Michael|date=21 April 2014|title=Have You Lost Your Mind?|url=https://www.newyorker.com/magazine/2014/04/28/have-you-lost-your-mind|magazine=The New Yorker|access-date=23 November 2023}}
*{{Cite magazine |date=18 January 1960 |title=Education: Joy in Giving |url=http://www.time.com/time/magazine/article/0,9171,828597,00.html |archive-url=https://web.archive.org/web/20110220012106/http://www.time.com/time/magazine/article/0,9171,828597,00.html |archive-date=20 February 2011 |access-date=2 April 2011 |magazine=Time|ref={{Harvid|Time 1960}}}}
*{{cite news| url= http://www.time.com/time/specials/2007/time100/article/0,28804,1595326_1615754_1615882,00.html| title=Michael J. Fox| date=3 May 2007| vauthors = Davis P| work=The Time 100| publisher=] |location=New York |access-date=2 April 2011 |archive-url= https://web.archive.org/web/20110425013526/http://www.time.com/time/specials/2007/time100/article/0,28804,1595326_1615754_1615882,00.html| archive-date=25 April 2011 }}
*{{cite news|url=https://www.theguardian.com/lifeandstyle/2009/apr/11/michael-j-fox-parkinsons|title='It's the gift that keeps on taking'|date=11 April 2009| vauthors = Brockes E |work=The Guardian|access-date=25 October 2010|url-status=live|archive-url=https://web.archive.org/web/20131008000425/http://www.theguardian.com/lifeandstyle/2009/apr/11/michael-j-fox-parkinsons|archive-date=8 October 2013}}

{{Refend}}


== External links ==
{{Sister project links|d=Q11085}}
* {{curlie|Health/Conditions_and_Diseases/Neurological_Disorders/Parkinson's_Disease/|Parkinson's Disease}}
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{{Medical condition classification and resources {{Medical condition classification and resources
| DiseasesDB = 9651 | DiseasesDB = 9651
| ICD10 = {{ICD10|G|20||g|20}}, {{ICD10|F|02|3|f|00}} | ICD11 = {{ICD11|8A00.0}}
| ICD10 = {{ICD10|G20}}, {{ICD10|F02.3}}
| ICD9 = {{ICD9|332}} | ICD9 = {{ICD9|332}}
| ICDO = | ICDO =
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|MeSH=D010300 |MeSH=D010300
| GeneReviewsNBK = NBK1223 | GeneReviewsNBK = NBK1223
| GeneReviewsName = Parkinson Disease Overview | GeneReviewsName = Parkinson Disease Overview
}} }}
{{Mental and behavioral disorders|selected=neurological}}
{{CNS diseases of the nervous system}}
{{Antiparkinson}} {{Antiparkinson}}
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Revision as of 07:57, 30 December 2024

Progressive neurodegenerative disease "Parkinson's" redirects here. For the medical journal, see Parkinson's Disease (journal). For other uses, see Parkinson's (disambiguation).

Medical condition
Parkinson's disease
Other namesIdiopathic or primary parkinsonism, hypokinetic rigid syndrome, paralysis agitans, shaking palsy
A. 1880s illustration of Parkinson's disease (PD)B. Mild motor-predominant PDC. Intermediate PDD. Diffuse malignant PD
SpecialtyNeurology Edit this on Wikidata
Symptoms
ComplicationsFalls, dementia, aspiration pneumonia
Usual onsetAge over 60
DurationLong-term
Risk factorsFamily history, dyspepsia, general anesthesia, pesticide exposure, head injuries
Diagnostic methodSymptomatic, medical imaging
Differential diagnosisDementia with Lewy bodies, progressive supranuclear palsy, essential tremor, antipsychotic use, fragile X-associated tremor/ataxia syndrome, Huntington's disease, dopamine-responsive dystonia, Wilson's disease
PreventionPhysical activity, nicotine, caffeine
TreatmentPhysical therapy, deep brain stimulation
MedicationL-DOPA, COMT inhibitors, AAAD inhibitors, dopamine agonists, MAO-B inhibitors
PrognosisNear-normal life expectancy
Frequency8.5 million (2019)
Named afterJames Parkinson

Parkinson's disease (PD), or simply Parkinson's, is a neurodegenerative disease primarily of the central nervous system, affecting both motor and non-motor systems. Symptoms typically develop gradually, with non-motor issues becoming more prevalent as the disease progresses. Common motor symptoms include tremors, bradykinesia (slowness of movement), rigidity, and balance difficulties, collectively termed parkinsonism. In later stages, Parkinson's disease dementia, falls, and neuropsychiatric problems such as sleep abnormalities, psychosis, mood swings, or behavioral changes may arise.

Most cases of Parkinson's disease are sporadic, though contributing factors have been identified. Pathophysiology involves progressive degeneration of nerve cells in the substantia nigra, a midbrain region that provides dopamine to the basal ganglia, a system involved in voluntary motor control. The cause of this cell death is poorly understood but involves the aggregation of alpha-synuclein into Lewy bodies within neurons. Other potential factors involve genetic and environmental influences, medications, lifestyle, and prior health conditions.

Diagnosis is primarily based on signs and symptoms, typically motor-related, identified through neurological examination. Medical imaging techniques like positron emission tomography can support the diagnosis. Parkinson's typically manifests in individuals over 60, with about one percent affected. In those younger than 50, it is termed "early-onset PD".

No cure for Parkinson's is known, and treatment focuses on alleviating symptoms. Initial treatment typically includes L-DOPA, MAO-B inhibitors, or dopamine agonists. As the disease progresses, these medications become less effective and may cause involuntary muscle movements. Diet and rehabilitation therapies can help improve symptoms. Deep brain stimulation is used to manage severe motor symptoms when drugs are ineffective. There is little evidence for treatments addressing non-motor symptoms, such as sleep disturbances and mood instability. Life expectancy for those with PD is near-normal but is decreased for early-onset.

Classification and terminology

See also: Parkinsonism and Parkinson-plus syndrome

Parkinson's disease (PD) is a neurodegenerative disease affecting both the central and peripheral nervous systems, characterized by the loss of dopamine-producing neurons in the substantia nigra region of the brain. It is classified as a synucleinopathy due to the abnormal accumulation of the protein alpha-synuclein, which aggregates into Lewy bodies within affected neurons.

The loss of dopamine-producing neurons in the substantia nigra initially presents as movement abnormalities, leading to Parkinson's further categorization as a movement disorder. In 30% of cases, disease progression leads to the cognitive decline known as Parkinson's disease dementia (PDD). Alongside dementia with Lewy bodies, PDD is one of the two subtypes of Lewy body dementia.

The four cardinal motor symptoms of Parkinson's—bradykinesia (slowed movements), postural instability, rigidity, and tremor—are called parkinsonism. These four symptoms are not exclusive to Parkinson's and can occur in many other conditions, including HIV infection and recreational drug use. Neurodegenerative diseases that feature parkinsonism but have distinct differences are grouped under the umbrella of Parkinson-plus syndromes or, alternatively, atypical parkinsonian disorders. Parkinson's disease can be attributed to genetic factors or be idiopathic, in which there is no clearly identifiable cause. The latter, also called sporadic Parkinson's, makes up some 85–90% of cases.

Signs and symptoms

Main article: Signs and symptoms of Parkinson's disease

Motor

See also: Parkinsonism Motor symptoms include a stooping posture, the "Parkinsonian gait", and micrographia—jagged, diminutive handwriting.

Although a wide spectrum of motor and non-motor symptoms appear in Parkinson's, the cardinal features remain tremor, bradykinesia, rigidity, and postural instability, collectively termed parkinsonism. Appearing in 70–75 percent of PD patients, tremor is often the predominant motor symptom. Resting tremor is the most common, but kinetic tremors—occurring during voluntary movements—and postural tremor—preventing upright, stable posture—also occur. Tremor largely affects the hands and feet: a classic parkinsonian tremor is "pill-rolling", a resting tremor in which the thumb and index finger make contact in a circular motion at 4–6 Hz frequency.

Bradykinesia describes difficulties in motor planning, beginning, and executing, resulting in overall slowed movement with reduced amplitude that affects sequential and simultaneous tasks. Bradykinesia can also lead to hypomimia, reduced facial expressions. Rigidity, also called rigor, refers to a feeling of stiffness and resistance to passive stretching of muscles that occurs in up to 89 percent of cases. Postural instability typically appears in later stages, leading to impaired balance and falls. Postural instability also leads to a forward stooping posture.

Beyond the cardinal four, other motor deficits, termed secondary motor symptoms, commonly occur. Notably, gait disturbances result in the Parkinsonian gait, which includes shuffling and paroxysmal deficits, where a normal gait is interrupted by rapid footsteps—known as festination—or sudden stops, impairing balance and causing falls. Most PD patients experience speech problems, including stuttering, hypophonic, "soft" speech, slurring, and festinating speech (rapid and poorly intelligible). Handwriting is commonly altered in Parkinson's, decreasing in size—known as micrographia—and becoming jagged and sharply fluctuating. Grip and dexterity are also impaired.

Non-motor

Neuropsychiatric and cognitive

Neuropsychiatric symptom prevalence in Parkinson's disease
Symptom
Prevalence (%)
Anxiety 40–50
Apathy 40
Depression 20–40
Impulse control disorders 36–60
Psychosis 15–30

Neuropsychiatric symptoms like anxiety, apathy, depression, hallucinations, and impulse control disorders occur in up to 60% of those with Parkinson's. They often precede motor symptoms and vary with disease progression. Non-motor fluctuations, including dysphoria, fatigue, and slowness of thought, are also common. Some neuropsychiatric symptoms are not directly caused by neurodegeneration but rather by its pharmacological management.

Cognitive impairments rank among the most prevalent and debilitating non-motor symptoms. These deficits may emerge in the early stages or before diagnosis, and their prevalence and severity tend to increase with disease progression. Ranging from mild cognitive impairment to severe Parkinson's disease dementia, these impairments include executive dysfunction, slowed cognitive processing speed, and disruptions in time perception and estimation.

Autonomic

Dysphagia—an autonomic failure—can lead to aspiration pneumonia (pictured).

Autonomic nervous system failures, known as dysautonomia, can appear at any stage of Parkinson's. They are among the most debilitating symptoms and greatly reduce quality of life. Although almost all PD patients suffer cardiovascular autonomic dysfunction, only some are symptomatic. Chiefly, orthostatic hypotension—a sustained blood pressure drop of at least 20 mmHg systolic or 10 mmHg diastolic after standing—occurs in 30–50 percent of cases. This can result in lightheadedness or fainting: subsequent falls are associated with higher morbidity and mortality.

Other autonomic failures include gastrointestinal issues like chronic constipation, impaired stomach emptying and subsequent nausea, excessive salivation, and dysphagia (difficulty swallowing): all greatly reduce quality of life. Dysphagia, for instance, can prevent pill swallowing and lead to aspiration pneumonia. Urinary incontinence, sexual dysfunction, and thermoregulatory dysfunction—including heat and cold intolerance and excessive sweating—also frequently occur.

Other non-motor symptoms

Sensory deficits appear in up to 90 percent of patients and are usually present at early stages. Nociceptive and neuropathic pain are common, with peripheral neuropathy affecting up to 55 percent of individuals. Visual impairments are also frequently observed, including deficits in visual acuity, color vision, eye coordination, and visual hallucinations. An impaired sense of smell is also prevalent. PD patients often struggle with spatial awareness, recognizing faces and emotions, and may experience challenges with reading and double vision.

Sleep disorders are highly prevalent in PD, affecting up to 98%. These disorders include insomnia, excessive daytime sleepiness, restless legs syndrome, REM sleep behavior disorder (RBD), and sleep-disordered breathing, many of which can be worsened by medication. RBD may begin years before the initial motor symptoms. Individual presentation of symptoms varies, although most people affected by PD show an altered circadian rhythm at some point of disease progression.

PD is also associated with a variety of skin disorders that include melanoma, seborrheic dermatitis, bullous pemphigoid, and rosacea. Seborrheic dermatitis is recognized as a premotor feature that indicates dysautonomia and demonstrates that PD can be detected not only by changes of nervous tissue, but tissue abnormalities outside the nervous system as well.

Causes

Main article: Causes of Parkinson's disease The protein alpha-synuclein aggregates into Lewy bodies and neurites. Structural model of alpha-synuclein (left), photomicrograph of Lewy bodies (right).

As of 2024, the cause of neurodegeneration in Parkinson's remains unclear, though it is believed to result from the interplay of genetic and environmental factors. The majority of cases are sporadic with no clearly identifiable cause, while approximately 5–10 percent are familial. Around a third of familial cases can be attributed to a single monogenic cause.

Molecularly, abnormal aggregation of alpha-synuclein is considered a key contributor to PD pathogenesis, although the trigger for this aggregation remains debated. Proteostasis disruption and the dysfunction of cell organelles, including endosomes, lysosomes, and mitochondria, are implicated in pathogenesis. Additionally, maladaptive immune and inflammatory responses are potential contributors. The substantial heterogeneity in PD presentation and progression suggests the involvement of multiple interacting triggers and pathogenic pathways.

Genetic

Ribbon diagram of parkin

Parkinson's can be narrowly defined as a genetic disease, as rare inherited gene variants have been firmly linked to monogenic PD, and the majority of sporadic cases carry variants that increase PD risk. PD heritability is estimated to range from 22 to 40 percent. Around 15 percent of diagnosed individuals have a family history, of which 5–10 percent can be attributed to a causative risk gene mutation. However, carrying one of these mutations may not lead to disease. Rates of familial PD vary by ethnicity: monogenic PD occurs in up to 40% of Arab-Berber patients and 20% of Ashkenazi Jewish patients.

As of 2024, around 90 genetic risk variants across 78 genomic loci have been identified. Notable risk variants include SNCA (which encodes alpha-synuclein), LRRK2, and VPS35 for autosomal dominant inheritance, and PRKN, PINK1, and DJ1 for autosomal recessive inheritance. LRRK2 is the most common autosomal dominant variant, responsible for 1–2 percent of all PD cases and 40 percent of familial cases. Parkin variants are associated with nearly half of recessive, early-onset monogenic PD. Mutations in the GBA1 gene, linked to Gaucher's disease, are found in 5–15 percent of PD cases. The GBA1 variant frequently leads to cognitive decline.

Environmental

See also: Environmental health and Exposome
Environmental toxicants like pesticides are believed to be a trigger for Parkinson's.

The limited heritability of Parkinson's strongly suggests environmental factors are involved, though identifying these risk factors and establishing causality is challenging due to PD's decade-long prodromal period. However, environmental toxicants such as air pollution, pesticides, and industrial solvents like trichloroethylene are strongly linked to Parkinson's.

Certain pesticides—like paraquat, glyphosate, and rotenone—are the most established environmental toxicants for Parkinson's and are likely causal. PD prevalence is strongly associated with local pesticide use, and many pesticides are mitochondrial toxins. Paraquat, for instance, structurally resembles metabolized MPTP, which selectively kills dopaminergic neurons by inhibiting mitochondrial complex 1 and is widely used to model PD. Pesticide exposure after diagnosis may also accelerate disease progression. Without pesticide exposure, an estimated 20 percent of all PD cases would be prevented.

Hypotheses

Prionic hypothesis

See also: Prion

The hallmark of Parkinson's is the formation of protein aggregates, beginning with alpha-synuclein fibrils and followed by Lewy bodies and Lewy neurites. The prion hypothesis suggests that alpha-synuclein aggregates are pathogenic and can spread to neighboring, healthy neurons and seed new aggregates. Some propose that the heterogeneity of PD may stem from different "strains" of alpha-synuclein aggregates and varying anatomical sites of origin. Alpha-synuclein propagation has been demonstrated in cell and animal models and is the most popular explanation for the progressive spread through specific neuronal systems. However, therapeutic efforts to clear alpha-synuclein have failed. Additionally, postmortem brain tissue analysis shows that alpha-synuclein pathology does not clearly progress through the nearest neural connections.

Braak's hypothesis

Main article: Parkinson's disease and gut-brain axis § Braak's hypothesis

In 2002, Heiko Braak and colleagues proposed that Parkinson's disease begins outside the brain and is triggered by a "neuroinvasion" of some unknown pathogen. The pathogen enters through the nasal cavity and is swallowed into the digestive tract, initiating Lewy pathology in both areas. This alpha-synuclein pathology may then travel from the gut to the central nervous system through the vagus nerve. This theory could explain the presence of Lewy pathology in both the enteric nervous system and olfactory tract neurons, as well as clinical symptoms like loss of small and gastrointestinal problems. It has also been suggested that environmental toxicants might be ingested in a similar manner to trigger PD.

Catecholaldehyde hypothesis

Main article: Catecholaldehyde hypothesis
The catecholaldehyde hypothesis argues that the dopamine metabolite DOPAL (pictured) triggers alpha-synuclein aggregation.

The enzyme monoamine oxidase (MAO) plays a central role in the metabolism of the neurotransmitter dopamine and other catecholamines. The catecholaldehyde hypothesis argues that the oxidation of dopamine by MAO into 3,4-dihydroxyphenylacetaldehyde (DOPAL) and hydrogen peroxide and the subsequent abnormal accumulation thereof leads to neurodegeneration. The theory posits that DOPAL interacts with alpha-synuclein and causes it to aggregate.

Mitochondrial dysfunction

Whether mitochondrial dysfunction is a cause or consequence of PD pathology remains unclear. Impaired ATP production, increased oxidative stress, and reduced calcium buffering may contribute to neurodegeneration. The finding that MPP—a respiratory complex I inhibitor and MPTP metabolite—caused parkinsonian symptoms strongly implied that mitochondria contributed to PD pathogenesis. Alpha-synuclein and toxicants like rotenone similarly disrupt respiratory complex I. Additionally, faulty gene variants involved in familial Parkinson's—including PINK1 and Parkin—prevent the elimination of dysfunctional mitochondria through mitophagy.

Neuroinflammation

Some hypothesize that neurodegeneration arises from a chronic neuroinflammatory state created by local activated microglia and infiltrating immune cells. Mitochondrial dysfunction may also drive immune activation, particularly in monogenic PD. Some autoimmune disorders increase the risk of developing PD, supporting an autoimmune contribution. Additionally, influenza and herpes simplex virus infections increase the risk of PD, possibly due to a viral protein resembling alpha-synuclein. Parkinson's risk is also decreased with immunosuppressants.

Pathophysiology

Main article: Pathophysiology of Parkinson's disease
Parkinson's results from the death of dopamine-releasing neurons in the substantia nigra pars compacta, seen by the loss of dark neuromelanin in the lower inset.

Parkinson's disease has two hallmark pathophysiological processes: the abnormal aggregation of alpha-synuclein that leads to Lewy pathology, and the degeneration of dopaminergic neurons in the substantia nigra pars compacta. The death of these neurons reduces available dopamine in the striatum, which in turn affects circuits controlling movement in the basal ganglia. By the time motor symptoms appear, 50–80 percent of all dopaminergic neurons in the substantia nigra have degenerated.

However, cell death and Lewy pathology are not limited to the substantia nigra. The six-stage Braak system holds that alpha-synuclein pathology begins in the olfactory bulb or outside the central nervous system in the enteric nervous system before ascending the brain stem. In the third Braak stage, Lewy body pathology appears in the substantia nigra, and, by the sixth step, Lewy pathology has spread to the limbic and neocortical regions. Although Braak staging offers a strong basis for PD progression, the Lewy pathology around 50 percent patients do not adhere to the predicted model. Indeed, Lewy pathology is highly variable and may be entirely absent in some PD patients.

Alpha-synuclein pathology

Further information: Protein aggregation and Lewy body
Lewy bodies and Lewy neurites stained brown in PD brain tissue

Alpha-synuclein is an intracellular protein typically localized to presynaptic terminals and involved in synaptic vesicle trafficking, intracellular transport, and neurotransmitter release. When misfolded, it can aggregate into oligomers and proto-fibrils that in turn lead to Lewy body formation. Due to their lower molecular weight, oligomers and proto-fibrils may disseminate and be transmitted to other cells more rapidly.

Lewy bodies consist of a fibrillar exterior and granular core. Although alpha-synuclein is the dominant proteinaceous component, the core contains mitochondrial and autophagosomal membrane components, suggesting a link with organelle dysfunction. It is unclear whether Lewy bodies themselves contribute to or are simply the result of PD pathogenesis: alpha-synuclein oligomers can independently mediate cell damage, and neurodegeneration can precede Lewy body formation.

Pathways involved in neurodegeneration

See also: Neurodegeneration § Mechanisms

Three major pathways—vesicular trafficking, lysosomal degradation, and mitochondrial maintenance—are known to be affected by and contribute to Parkinson's pathogenesis, with all three linked to alpha-synuclein. High risk gene variants also impair all three of these processes. All steps of vesicular trafficking are impaired by alpha-synuclein. It blocks endoplasmic reticulum (ER) vesicles from reaching the Golgi—leading to ER stress—and Golgi vesicles from reaching the lysosome, preventing alpha-synuclein degradation and leading to its build-up. Risky gene variants, chiefly GBA, further compromise lysosomal function. Although the mechanism is not well established, alpha-synuclein can impair mitochondrial function and cause subsequent oxidative stress. Mitochondrial dysfunction can in turn lead to further alpha-synuclein accumulation in a positive feedback loop. Microglial activation, possibly caused by alpha-synuclein, is also strongly indicated.

Risk factors

Positive risk factors

As 90 percent of Parkinson's cases are sporadic, the identification of the risk factors that may influence disease progression or severity is critical. The most significant risk factor in developing PD is age, with a prevalence of 1 percent in those aged over 65 and approximately 4.3 percent in age over 85. Traumatic brain injury significant increases PD risk, especially if recent. Dairy consumption correlates with a higher risk, possibly due to contaminants like heptachlor epoxide. Although the connection is unclear, melanoma diagnosis is associated with an approximately 45 percent risk increase. There is also an association between methamphetamine use and PD risk.

Protective factors

Higher blood concentration of urate—a potent antioxidant—are associated with a lower risk of Parkinson's.

Although no compounds or activities have been mechanistically established as neuroprotective for Parkinson's, several factors have been found to be associated with a decreased risk. Tobacco use and smoking is strongly associated with a decreased risk, reducing the chance of developing PD by up to 70%. Various tobacco and smoke components have been hypothesized to be neuroprotective, including nicotine, carbon monoxide, and monoamine oxidase B inhibitors. Consumption of coffee, tea, or caffeine is also strongly associated with neuroprotection. Prescribed adrenergic antagonists like terazosin may reduce risk.

Although findings have varied, usage of nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen may be neuroprotective. Calcium channel blockers may also have a protective effect, with a 22% risk reduction reported. Higher blood concentrations of urate—a potent antioxidant—have been proposed to be neuroprotective. Although longitudinal studies observe a slight decrease in PD risk among those who consume alcohol—possibly due to alcohol's urate-increasing effect—alcohol abuse may increase risk.

Diagnosis

Diagnosis of Parkinson's disease is largely clinical, relying on medical history and examination of symptoms, with an emphasis on symptoms that appear in later stages. Although early stage diagnosis is not reliable, prodromal diagnosis may consider previous family history of Parkinson's and possible early symptoms like rapid eye movement sleep behavior disorder (RBD), reduced sense of smell, and gastrointestinal issues. Isolated RBD is a particularly significant sign as 90% of those affected will develop some form of neurodegenerative parkinsonism. Diagnosis in later stages requires the manifestation of parkinsonism, specifically bradykinesia and rigidity or tremor. Further support includes other motor and non-motor symptoms and genetic profiling.

A PD diagnosis is typically confirmed by two of the following criteria: responsiveness to levodopa, resting tremor, levodopa-induced dyskinesia, or with dopamine transporter single-proton emission computed tomography. If these criteria are not met, atypical parkinsonism is considered. However, definitive diagnoses can only be made post-mortem through pathological analysis. Misdiagnosis is common, with a reported error rate of near 25 percent, and diagnoses often change during follow-ups. Diagnosis can be further complicated by multiple overlapping conditions.

Imaging

Reduced radioisotopic F-DOPA uptake in the striatum of a Parkinson's patient, captured through PET

Diagnosis can be aided by molecular imaging techniques such as magnetic resonance imaging (MRI), positron emission tomography (PET), and single-photon emission computed tomography (SPECT). As both conventional MRI and computed tomography (CT) scans are usually normal in patients with early PD, they can be used to exclude other pathologies that cause parkinsonism. Diffusion MRI can differentiate PD from multiple systems atrophy (MSA). Emerging MRI techniques of at least 3.0 T field strength—including neuromelanin-MRI, 1H-MRSI, and resting state fMRI—may detect abnormalities in the substantia nigra, nigrostriatal pathway, and elsewhere.

Unlike MRI, PET and SPECT use radioisotopes for imaging. Both techniques can aid diagnosis by characterizing PD-associated alterations in the metabolism and transport of dopamine in the basal ganglia. Largely used outside the United States, iodine-123-meta-iodobenzylguanidine myocardial scintigraphy can assess heart muscle denervation to support a PD diagnosis.

Differential diagnosis

An MRI finding that is seen commonly in Multiple System atrophy. This occurs on the Pons.
The "Hot Cross Bun" sign, found in multiple system atrophy with MRI
See also: Parkinson-plus syndrome

Differential diagnosis of Parkinson's is among the most difficult in neurology. Differentiating early PD from atypical parkinsonian disorders is a major difficulty. In their initial stages, PD can be difficult to distinguish from the atypical neurodegenerative parkinsonisms, including MSA, dementia with Lewy bodies, and the tauopathies progressive supranuclear palsy and corticobasal degeneration. Other conditions that may present similarly to PD include vascular parkinsonism, Alzheimer's disease, and frontotemporal dementia.

The International Parkinson and Movement Disorder Society has proposed a set of criteria that, unlike the standard Queen's Square Brain Bank Criteria, includes non-exclusionary "red-flag" clinical features that may not suggest Parkinson's. A large number of "red flags" have been proposed and adopted for various conditions that might mimic the symptoms of PD. Diagnostic tests, including gene sequencing, molecular imaging techniques, and assessment of smell may also distinguish PD. MRI is particularly powerful due to several unique features for atypical parkinsonisms. Key distinguishing symptoms and features include:

Disorder Distinguishing symptoms and features
Corticobasal syndrome Levodopa resistance, myoclonus, dystonia, corticosensory loss, alien limb phenomenon, apraxia, and non-fluent aphasia
Dementia with Lewy bodies Levodopa resistance, cognitive predominance before motor symptoms, and fluctuating cognitive symptoms
Essential tremor Tremor that worsens with action, normal SPECT scan
Multiple system atrophy Levodopa resistance, rapidly progressive, autonomic failure, stridor, present Babinski sign, cerebellar ataxia, and specific MRI findings like the "Hot Cross Bun"
Progressive supranuclear palsy Levodopa resistance, restrictive vertical gaze, pseudobulbar crying, eyelid twitching, specific MRI findings, and early and different postural difficulties

Management

Main article: Management of Parkinson's disease

As of 2024, no disease-modifying therapies exist that reverse or slow neurodegeneration, processes respectively termed neurorestoration and neuroprotection. Patients are typically managed with a holistic approach that combines lifestyle modifications with physical therapy. Current pharmacological interventions purely target symptoms, by either increasing endogenous dopamine levels or directly mimicking dopamine's effect on the patient's brain. These include dopamine agonists, MAO-B inhibitors, and levodopa: the most widely used and effective drug. The optimal time to initiate pharmacological treatment is debated, but initial dopamine agonist and MAO-B inhibitor treatment and later levodopa therapy is common. Invasive procedures such as deep brain stimulation may be used for patients that do not respond to medication.

Medications

Levodopa

LCE (levodopa/carbidopa/entacapone) pills contain a cocktail of the dopamine precursor L-DOPA and COMT and AAAD inhibitors.

Levodopa (L-DOPA) is the most widely used and the most effective therapy—the gold standard—for Parkinson's treatment. The compound occurs naturally and is the immediate precursor for dopamine synthesis in the dopaminergic neurons of the substantia nigra. Levodopa administration reduces the dopamine deficiency, alleviating parkinsonian symptoms.

Despite its efficacy, levodopa poses several challenges and has been called the "pharmacologist's nightmare". Its metabolism outside the brain by aromatic L-amino acid decarboxylase (AAAD) and catechol-O-methyltransferase (COMT) can cause nausea and vomiting; inhibitors like carbidopa, entacapone, and benserazide are usually taken with levodopa to mitigate these effects. Symptoms may become unresponsive to levodopa, with sudden changes between a state of mobility ("ON time") and immobility ("OFF time"). Long-term levodopa use may also induce dyskinesia and motor fluctuations. Although this often causes levodopa use to be delayed to later stages, earlier administration leads to improved motor function and quality of life.

Dopamine agonists

Dopamine agonists are an alternative or complement for levodopa therapy. They activate dopamine receptors in the striatum, with reduced risk of motor fluctuations and dyskinesia. Ergot dopamine agonists were commonly used, but have been largely replaced with non-ergot compounds due to severe adverse effects like pulmonary fibrosis and cardiovascular issues. Non-ergot agonists are efficacious in both early and late stage Parkinson's, The agonist apomorphine is often used for drug-resistant OFF time in later-stage PD. However, after five years of use, impulse control disorders may occur in over 40 percent of PD patients taking dopamine agonists. A problematic, narcotic-like withdrawal effect may occur when agonist use is reduced or stopped. Compared to levodopa, dopamine agonists are more likely to cause fatigue, daytime sleepiness, and hallucinations.

MAO-B inhibitors

MAO-B inhibitors—such as safinamide, selegiline and rasagiline—increase the amount of dopamine in the basal ganglia by inhibiting the activity of monoamine oxidase B, an enzyme that breaks down dopamine. These compounds mildly alleviate motor symptoms when used as monotherapy but can also be used with levodopa and can be used at any disease stage. When used with levodopa, time spent in the off phase is reduced. Selegiline has been shown to delay the need for initial levodopa, suggesting that it might be neuroprotective and slow the progression of the disease. Common side effects are nausea, dizziness, insomnia, sleepiness, and (in selegiline and rasagiline) orthostatic hypotension. MAO-Bs are known to increase serotonin and cause a potentially dangerous condition known as serotonin syndrome.

Other drugs

Treatments for non-motor symptoms of PD have not been well studied and many medications are used off-label. A diverse range of symptoms beyond those related to motor function can be treated pharmaceutically. Examples include cholinesterase inhibitors for cognitive impairment and modafinil for excessive daytime sleepiness. Fludrocortisone, midodrine and droxidopa are commonly used off label for orthostatic hypotension related to autonomic dysfunction. Sublingual atropine or botulinum toxin injections may be used off-label for drooling. SSRIs and SNRIs are often used for depression related to PD, but there is a risk of serotonin syndrome with the SSRI or SNRI antidepressants. Doxepin and rasagline may reduce physical fatigue in PD. Other treatments have received government approval, such as the first FDA-approved treatment for PD psychosis, pimavanserin. Although its efficacy is inferior to off-label clozapine, it has significantly fewer side effects.

Invasive interventions

Further information: Deep brain stimulation
Placement of an electrode into the brain for deep brain stimulation.

Surgery for Parkinson's first appeared in the 19th century and by the 1960s had evolved into ablative brain surgery that lesioned the basal ganglia, thalamus or globus pallidus (a pallidotomy). The discovery of L-DOPA for PD treatment caused ablative therapies to largely disappear. Ablative surgeries experienced a resurgence in the 1990s but were quickly superseded by newly-developed deep brain stimulation (DBS). Although gamma knife and high-intensity focused ultrasound surgeries have been developed for pallidotomies and thalamotomies, their use remains rare.

DBS involves the implantation of electrodes called neurostimulators, which sends electrical impulses to specific parts of the brain. DBS for the subthalamic nucleus and globus pallidus interna has high efficacy for up to 2 years, but longterm efficacy is unclear and likely decreases with time. DBS typically targets rigidity and tremor, and is recommended for PD patients who are intolerant or do not respond to medication. Cognitive impairment is the most common exclusion criteria.

Rehabilitation

Further information: Management of Parkinson's disease § Rehabilitation
A Parkinson's patient on a tricycle
Exercise, like the tricycle ride of this PD patient, is often recommended.

Although pharmacological therapies can improve symptoms, patients' autonomy and ability to perform everyday tasks is still reduced by PD. As a result, rehabilitation is often useful. However, the scientific support for any single rehabilitation treatment is limited.

Exercise programs are often recommended, with preliminary evidence of efficacy. Regular physical exercise with or without physical therapy can be beneficial to maintain and improve mobility, flexibility, strength, gait speed, and quality of life. Aerobic, mind-body, and resistance training may be beneficial in alleviating PD-associated depression and anxiety. Strength training may increase manual dexterity and strength, facilitating daily tasks that require grasping objects.

In improving flexibility and range of motion for people experiencing rigidity, generalized relaxation techniques such as gentle rocking have been found to decrease excessive muscle tension. Other effective techniques to promote relaxation include slow rotational movements of the extremities and trunk, rhythmic initiation, diaphragmatic breathing, and meditation. Deep diaphragmatic breathing may also improve chest-wall mobility and vital capacity decreased by the stooped posture and respiratory dysfunctions of advanced Parkinson's. Rehabilitation techniques targeting gait and the challenges posed by bradykinesia, shuffling, and decreased arm swing include pole walking, treadmill walking, and marching exercises.

Speech therapies such as the Lee Silverman voice treatment may reduce the effect of speech disorders associated with PD. Occupational therapy is another rehabilitation strategy and can improve quality of life by enabling PD patients to find engaging activities and communal roles, adapt to their living environment, and improving domestic and work abilities.

Diet

Parkinson's poses digestive problems like constipation and prolonged emptying of stomach contents, and a balanced diet with periodical nutritional assessments is recommended to avoid weight loss or gain and minimize the consequences of gastrointestinal dysfunction. In particular, a Mediterranean diet is advised and may slow disease progression. As it can compete for uptake with amino acids derived from protein, levodopa should be taken 30 minutes before meals to minimize such competition. Low protein diets may also be needed by later stages. As the disease advances, swallowing difficulties often arise. Using thickening agents for liquid intake and an upright posture when eating may be useful; both measures reduce the risk of choking. Gastrostomy can be used to deliver food directly into the stomach. Increased water and fiber intake is used to treat constipation.

Palliative care

As Parkinson's is incurable, palliative care aims to improve the quality of life for both the patient and family by alleviating the symptoms and stress associated with illness. Early integration of palliative care into the disease course is recommended, rather than delaying until later stages. Palliative care specialists can help with physical symptoms, emotional factors such as loss of function and jobs, depression, fear, as well as existential concerns. Palliative care team members also help guide patients and families on difficult decisions caused by disease progression, such as wishes for a feeding tube, noninvasive ventilator or tracheostomy, use of cardiopulmonary resuscitation, and entering hospice care.

Prognosis

See also: Unified Parkinson's disease rating scale
Prognosis of PD subtypes
Parkinson's subtype Mean years post-diagnosis until:
Severe cognitive or movement abnormalities Death
Mild-motor predominant 14.3 20.2
Intermediate 8.2 13.1
Diffuse malignant 3.5 8.1

As Parkinson's is a heterogeneous condition with multiple etiologies, prognostication can be difficult and prognoses can be highly variable. On average, life expectancy is reduced in those with Parkinson's, with younger age of onset resulting in greater life expectancy decreases. Although PD subtype categorization is controversial, the 2017 Parkinson's Progression Markers Initiative study identified three broad scorable subtypes of increasing severity and more rapid progression: mild-motor predominant, intermediate, and diffuse malignant. Mean years of survival post-diagnosis were 20.2, 13.1, and 8.1.

Around 30% of Parkinson's patients develop dementia, and is 12 times more likely to occur in elderly patients of those with severe PD. Dementia is less likely to arise in patients with tremor-dominant PD. Parkinson's disease dementia is associated with a reduced quality of life in people with PD and their caregivers, increased mortality, and a higher probability of needing nursing home care.

The incidence rate of falls in Parkinson's patients is approximately 45 to 68%, thrice that of healthy individuals, and half of such falls result in serious secondary injuries. Falls increase morbidity and mortality. Around 90% of those with PD develop hypokinetic dysarthria, which worsens with disease progression and can hinder communication. Additionally, over 80% of PD patients develop dysphagia: consequent inhalation of gastric and oropharyngeal secretions can lead to aspiration pneumonia. Aspiration pneumonia is responsible for 70% of deaths in those with PD.

Epidemiology

Agricultural areas are associated with higher Parkinson's prevalence, possibly due to exposure to pesticides and industrial waste.

As of 2024, Parkinson's is the second most common neurodegenerative disease and the fastest-growing in total number of cases. As of 2023, global prevalence was estimated to be 1.51 per 1000. Although it is around 40% more common in men, age is the dominant predeterminant of Parkinson's. Consequently, as global life expectancy has increased, Parkinson's disease prevalence has also risen, with an estimated increase in cases by 74% from 1990 to 2016. The total number is predicted to rise to over 12 million patients by 2040. Some label this a pandemic.

This increase may be due to a number of global factors, including prolonged life expectancy, increased industrialisation, and decreased smoking. Although genetics is the sole factor in a minority of cases, most cases of Parkinson's are likely a result of gene-environment interactions: concordance studies with twins have found Parkinson's heritability to be just 30%. The influence of multiple genetic and environmental factors complicates epidemiological efforts.

Relative to Europe and North America, disease prevalence is lower in Africa but similar in Latin America. Although China is predicted to have nearly half of the global Parkinson's population by 2030, estimates of prevalence in Asia vary. Potential explanations for these geographic differences include genetic variation, environmental factors, health care access, and life expectancy. Although PD incidence and prevalence may vary by race and ethnicity, significant disparities in care, diagnosis, and study participation limit generalizability and lead to conflicting results. Within the United States, high rates of PD have been identified in the Midwest, the South, and agricultural regions of other states: collectively termed the "PD belt". The association between rural residence and Parkinson's has been hypothesized to be caused by environmental factors like herbicides, pesticides, and industrial waste.

History

Main article: History of Parkinson's disease In 1877, Jean-Martin Charcot (left) named the disease for James Parkinson, credited as the first to comprehensively describe it. Patient Pierre D. (right) served as the model for William Gowers' widely distributed illustration of Parkinson's disease.

In 1817, English physician James Parkinson published the first full medical description of the disease as a neurological syndrome in his monograph An Essay on the Shaking Palsy. He presented six clinical cases, including three he had observed on the streets near Hoxton Square in London. Parkinson described three cardinal symptoms: tremor, postural instability and "paralysis" (undistinguished from rigidity or bradykinesia), and speculated that the disease was caused by trauma to the spinal cord.

There was little discussion or investigation of the "shaking palsy" until 1861, when Frenchman Jean-Martin Charcot—regarded as the father of neurology—began expanding Parkinson's description, adding bradykinesia as one of the four cardinal symptoms. In 1877, Charcot renamed the disease after Parkinson, as not all patients displayed the tremor suggested by "shaking palsy". Subsequent neurologists who made early advances to the understanding of Parkinson's include Armand Trousseau, William Gowers, Samuel Kinnier Wilson, and Wilhelm Erb.

The Internal Classic (c. 425–221 BC), a Chinese text credited to the Yellow Emperor (pictured), details a disease with strikingly parkinsonian symptoms.

Although Parkinson is typically credited with the first detailed description of PD, many previous texts reference some of the disease's clinical signs. In his essay, Parkinson himself acknowledged partial descriptions by Galen, William Cullen, Johann Juncker, and others. Possible earlier but incomplete descriptions include a Nineteenth Dynasty Egyptian papyrus, the ayurvedic text Charaka Samhita, Ecclesiastes 12:3, and a discussion of tremors by Leonardo da Vinci. Multiple traditional Chinese medicine texts may include references to PD, including a discussion in the Yellow Emperor's Internal Classic (c. 425–221 BC) of a disease with symptoms of tremor, stiffness, staring, and stooped posture. In 2009, a systematic description of PD was found in the Hungarian medical text Pax corporis written by Ferenc Pápai Páriz in 1690, some 120 years before Parkinson. Although Páriz correctly described all four cardinal signs, it was only published in Hungarian and was not widely distributed.

In 1912, Frederic Lewy described microscopic particles in affected brains, later named Lewy bodies. In 1919, Konstantin Tretiakoff reported that the substantia nigra was the main brain structure affected, corroborated by Rolf Hassler in 1938. The underlying changes in dopamine signaling were identified in the 1950s, largely by Arvid Carlsson and Oleh Hornykiewicz. In 1997, Polymeropoulos and colleagues at the NIH discovered the first gene for PD, SNCA, which encodes alpha-synuclein. Alpha-synuclein was in turn found to be the main component of Lewy bodies by Spillantini, Trojanowski, Goedert, and others. Anticholinergics and surgery were the only treatments until the use of levodopa, which, although first synthesized by Casimir Funk in 1911, did not enter clinical use until 1967. By the late 1980s, deep brain stimulation introduced by Alim Louis Benabid and colleagues at Grenoble, France, emerged as an additional treatment.

Society and culture

A sketch showing hypomimia, a blank, expressionless face
The reduced ability to facially express emotions—as depicted here by French anatomist Paul Richer in 1888—can harm social well-being.

Social impact

For some people with PD, masked facial expressions and difficulty moderating facial expressions of emotion or recognizing other people's facial expressions can impact social well-being. As the condition progresses, tremor, other motor symptoms, difficulty communicating, or mobility issues may interfere with social engagement, causing individuals with PD to feel isolated. Public perception and awareness of PD symptoms such as shaking, hallucinating, slurring speech, and being off balance is lacking in some countries and can lead to stigma.

Cost

The economic cost of Parkinson's to both individuals and society is high. Globally, most government health insurance plans do not cover Parkinson's therapies, requiring patients to pay out-of-pocket. Indirect costs include lifetime earnings losses due to premature death, productivity losses, and caregiver burdens. The duration and progessive nature of PD can place a heavy burden on caregivers: family members like spouses dedicate around 22 hours per week to care.

In 2010, the total economic burden of Parkinson's across Europe, including indirect and direct medical costs, was estimated to be €13.9 billion (US $14.9 billion) in 2010. The total burden in the United States was estimated to be $51.9 billion in 2017, and is project to surpass $79 billion by 2037. However, as of 2022, no rigorous economic surveys had been performed for low or middle income nations. Regardless, preventative care has been identified as crucial to prevent the rapidly increasing incidence of Parkinson's from overwhelming national health systems.

Advocacy

Scottish rugby player Gavin Hastings signs a pledge from the World Parkinson Congress

The birthday of James Parkinson, 11 April, has been designated as World Parkinson's Day. A red tulip was chosen by international organizations as the symbol of the disease in 2005; it represents the 'James Parkinson' tulip cultivar, registered in 1981 by a Dutch horticulturalist.

Advocacy organizations include the National Parkinson Foundation, which has provided more than $180 million in care, research, and support services since 1982, Parkinson's Disease Foundation, which has distributed more than $115 million for research and nearly $50 million for education and advocacy programs since its founding in 1957 by William Black; the American Parkinson Disease Association, founded in 1961; and the European Parkinson's Disease Association, founded in 1992.

Notable cases

Main article: List of people diagnosed with Parkinson's disease
Actor Michael J. Fox and boxer Muhammad Ali (center) are pictured in 2002 speaking before the US Senate to urge increased funding for Parkinson's research.

In the 21st century, the diagnosis of Parkinson's among notable figures has increased the public's understanding of the disorder. Actor Michael J. Fox was diagnosed with PD at 29 years old, and has used his diagnosis to increase awareness of the disease. To illustrate the effects of the disease, Fox has appeared without medication in television roles and before the United States Congress without medication. The Michael J. Fox Foundation, which he founded in 2000, has raised over $2 billion for Parkinson's research.

Boxer Muhammad Ali showed signs of PD when he was 38, but was undiagnosed until he was 42, and has been called the "world's most famous Parkinson's patient". Whether he had PD or parkinsonism related to boxing is unresolved. Cyclist and Olympic medalist Davis Phinney, diagnosed with Parkinson's at 40, started the Davis Phinney Foundation in 2004 to support PD research.

Several historical figures have been theorized to have had Parkinson's, often framed in the industriousness and inflexibility of the so-called "Parkinsonian personality". For instance, English philosopher Thomas Hobbes was diagnosed with "shaking palsy"—assumed to have been Parkinson's—but continued writing works such as Leviathan. Adolf Hitler is widely believed to have had Parkinson's, and the condition may have influenced his decision making. Mao Zedong was also reported to have died from the disorder.

Clinical research

Main article: Research in Parkinson's disease
Astronaut Alexander Gerst conducts Parkinson's research aboard the International Space Station in 2018

As of 2024, no disease-modifying therapies exist that reverse or slow the progression of Parkinson's. Active research directions include the search for new animal models of the disease and development and trial of gene therapy, stem cell transplants, and neuroprotective agents. Improved treatments will likely combine therapeutic strategies to manage symptoms and enhance outcomes. Reliable biomarkers are needed for early diagnosis, and research criteria for their identification have been established.

Neuroprotective treatments

See also: Anti-α-synuclein drug

Anti-alpha-synuclein drugs that prevent alpha-synuclein oligomerization and aggregation or promote their clearance are under active investigation, and potential therapeutic strategies include small molecules and immunotherapies like vaccines and monoclonal antibodies. While immunotherapies show promise, their effiacy is often inconsistent. Anti-inflammatory drugs that target NLRP3 and the JAK-STAT signaling pathway offer another potential therapeutic approach.

As the gut microbiome in PD is often disrupted and produces toxic compounds, fecal microbiota transplants might restore a healthy microbiome and alleviate various motor and non-motor symptoms. Neurotrophic factorspeptides that enhance the growth, maturation, and survival of neurons—show modest results but require invasive surgical administration. Viral vectors may represent a more feasible delivery platform. Calcium channel blockers may restore the calcium imbalance present in Parkinson's, and are being investigated as a neuroprotective treatment. Other therapies, like deferiprone, may reduce the abnormal accumulation of iron in PD.

Cell-based therapies

Main article: Cell-based therapies for Parkinson's disease Researchers at Argonne National Laboratory examining induced pluripotent stem cellsResearchers at Argonne National Laboratory examine induced pluripotent stem cells (iPSCs) for use in Parkinson's and other diseases: the action potentials of one such iPSC differentiated into a dopaminergic neuron are visible at right.

In contrast to other neurodegenerative disorders, many Parkinson's symptoms can be attributed to the loss of a single cell type. Consequently, dopaminergic neuron regeneration is a promising therapeutic approach. Although most initial research sought to generate dopaminergic neuron precursor cells from fetal brain tissue, pluripotent stem cells—particularly induced pluripotent stem cells (iPSCs)—have become an increasingly popular tissue source.

Both fetal and iPSC-derived DA neurons have been transplanted into patients in clinical trials. Although some patients see improvements, the results are highly variable. Adverse effects, such as dyskinesia arising from excess dopamine release by the transplanted tissues, have also been observed.

Gene therapy

Main article: Gene therapy in Parkinson's disease

Gene therapy for Parkinson's seeks to restore the healthy function of dopaminergic neurons in the substantia nigra by delivering genetic material—typically through a viral vector—to these diseased cells. This material may deilver a functional, wildtype version of a gene, or knockdown a pathological variants. Experimental gene therapies for PD have aimed to increase the expression of growth factors or enzymes involved in dopamine synthesis, like tyrosine hydroxylase. The one-time delivery of genes circumvents the recurrent invasive administration required to administer some peptides and proteins to the brain. MicroRNAs are an emerging PD gene therapy platform that may serve as an alternative to viral vectors.

Notes and references

Notes

  1. These inhibitors do not cross the blood brain barrier and thus do not prevent levodopa metabolism there.
  2. Defined as the onset of development of recurrent falls, wheelchair dependence, dementia, or facility placement.

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Antiparkinson agents (N04)
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