Parkinsonism is a general term used to define a syndrome manifest as bradykinesia (slowness of voluntary movements) with rigidity and/or tremor; it has a wide differential diagnosis (Table 183-1). Parkinson's disease (PD) is idiopathic parkinsonism without evidence of more widespread neurologic involvement. PD afflicts >1 million individuals in the United States. Mean age of onset is about 60 years; course progressive over 10-25 years. Tremor (pill rolling of hands) at rest (4-6 Hz). Presentation with tremor confined to one limb or one side of body is common. Other findings: rigidity (cogwheelingincreased ratchet-like resistance to passive limb movements), bradykinesia, fixed expressionless face (facial masking) with reduced frequency of blinking, hypophonic voice, drooling, impaired rapid alternating movements, micrographia (small handwriting), reduced arm swing, and flexed stooped posture with walking, shuffling gait, difficulty initiating or stopping walking, en-bloc turning (multiple small steps required to turn), retropulsion (tendency to fall backwards). Nonmotor aspects of PD include depression and anxiety, cognitive impairment, sleep disturbances, sensation of inner restlessness, loss of smell (anosmia), and disturbances of autonomic function. Normal muscular strength, deep tendon reflexes, and sensory examination. Diagnosis based on history and examination; neuroimaging, EEG, and CSF studies usually normal for age.