(1) A neurologic syndrome usually resulting from deficiency of the neurotransmitter dopamine as the consequence of degenerative, vascular, or inflammatory changes in the basal ganglia; characterized by rhythmic muscular tremors, rigidity of movement, festination, droopy posture, and masklike facies. SYN: Parkinson disease, shaking palsy, trembling palsy. (2) A syndrome similar to parkinsonism. Some features seen with Parkinson disease that occur with other disorders (e.g., progressive supranuclear palsy) or as a side effect of certain medications (e.g., antipsychotic drugs). [J. Parkinson]