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Medical Definition of Parkinson disease
1. Progressive, degenerative disease of unknown aetiology characterised by rhythmic tremor of the limbs, stooped posture, slowness of voluntary movements, and masklike facial expression. Pathologically there is nerve cell loss in the melanin-containing cells in the brainstem and a corresponding reduction in dopamine levels in the corpus striatum. Lewy bodies are present in the substantia nigra and locus coeruleus. (12 Dec 1998)