Parkinson disease is a neurodegenerative disorder caused by loss of dopaminergic cells. Average age of onset is 60 years, although it can less commonly affect individuals younger than 50 (early- or young-onset Parkinson disease). There is a 2:1 male-to-female ratio. Cardinal symptoms include rest tremor, rigidity, bradykinesia, and postural and gait instability. Symptoms often start unilaterally but typically progress to bilateral involvement. Foot cramps are a common early symptom. Other common signs and symptoms include anosmia, constipation, rapid-eye-movement sleep behavior disorder (RBD), micrographia, decreased finger dexterity, reduced arm swing, masked facies, hypophonia, drooling, dysphagia, cognitive impairment, depression, anxiety, weight loss, and autonomic dysfunction. "Nonmotor" symptoms may also include psychosis (eg, visual hallucinations, delusions).

The disease is progressive. Speed of progression is variable among patients, although it is generally slow (years), such that significant changes over less than a year's time should prompt consideration of other diagnoses. Ten to twenty percent of cases have a genetic propensity, often related to autosomal recessive mutations in the Parkin gene.

Several environmental factors are linked to Parkinson disease including certain pesticides, drinking well water, and exposure to industrial solvents like trichloroethylene, which are widely used in degreasing and dry cleaning.

Related topics: parkinsonism, dementia