Parkinson's Disease Parkinson’s disease (PD) is a movement disorder. In people with PD, a vital chemical in the brain called dopamine is gradually reduced. This brings on symptoms of tremor, slowness in movement, stiff limbs, and walking or balance problems. PD progresses slowly. Many treatments can reduce the symptoms and improve quality of life. The cause of PD is still unknown. Researchers think that both genes and environment may play a role. The disorder is due to a loss of nerve cells in an area deep within the brain called the substantia nigra. This area produces the chemical dopamine. The main symptoms of PD are: •Rigidity, or stiffness, in arms and legs •Tremor that is often most noticeable when the affected limb is at rest •Poor balance and coordination •Bradykinesia etc. No laboratory test or brain scan can definitively diagnose PD. Your physician will make a diagnosis based on all of your symptoms and your neurologic examination. It is vital to be diagnosed by a physician experienced in treating the disorder. Neurologists are physicians who can make a diagnosis.