Parkinsonism following encephalitis, historically seen as a sequella of encephalitis lethargica (Von Economo encephalitis). The early age of onset, the rapid progression of symptoms followed by stabilization, and the presence of a variety of other neurological disorders (e.g., sociopathic behavior; tics; MUSCLE SPASMS; oculogyric crises; hyperphagia; and bizarre movements) distinguish this condition from primary parkinson disease. Pathologic features include neuronal loss and gliosis concentrated in the mesencephalon; subthalamus; and hypothalamus. (From Adams et al., Principles of neurology, 6th ed, p754)