A syndrome of poverty and slowness (bradykinesia) of voluntary movement with "resting" tremor, stooped posture, rigidity, soft voice, and an abnormal gait consisting of small, shuffling steps with difficulty in retaining balance, especially when changing directions. The motor problems reflect degeneration of dopamine neurons in the substantia nigra compacta; its cause is unknown. Parkinsonism is a general term for conditions with some of these features.