Parkinson's Disease Overview

Parkinson's disease (PD) is a chronic and progressive disorder that affects approximately one million people in the United States and more than five million people worldwide. It is the second most common neurodegenerative disease, after Alzheimer's. The average age of onset is 62. Caused by the death of the dopamine-producing cells in the portion of the brain called the substantia nigra, PD is characterized by both motor and nonmotor symptoms. Motor symptoms include tremor, rigidity and slow movement ("bradykinesia"). Although symptoms may be mild at first, as the disease progresses motor complications typically increase. Nonmotor symptoms can include depression, anxiety, urinary problems and constipation, hallucinations, sleep disorders and dementia. Currently, there is no cure and no therapy that will slow disease progression.


PD is usually diagnosed based on symptoms and a physical examination. Although it is most commonly diagnosed in the elderly, it can occur in people who are much younger. PD can be difficult to diagnose, because there is no biomarker for the presence of the disease; instead, diagnoses are made based on symptoms that may also be characteristic of other neurodegenerative diseases.


Because PD is both chronic and progressive, symptoms become worse over time and if the disease is not treated it will eventually lead to complete disability and early death. The severity of symptoms varies among patients; some patients experience only minor motor effects, while others may become profoundly disabled. Several rating scales are used to evaluate the progression of disease and the effect of treatment. The most widely used is the Unified Parkinson's Disease Rating Scale.