A progressive degenerative disorder of the central nervous system characterized by loss of dopamine producing neurons in the substantia nigra and the presence of Lewy bodies in the substantia nigra and locus coeruleus. Signs and symptoms include tremor which is most pronounced during rest, muscle rigidity, slowing of the voluntary movements, a tendency to fall back, and a mask-like facial expression. The disease is Parkinson disease (Monarch Disease Ontology id MONDO_0005180). Also known as: PD, Parkinson's disease, paralysis agitans.