Neuropsychiatric condition with onset typically in middle or old age; gradual onset/progression of affective disturbances (agitation, depression, involuntary crying and laughing); neurologic disturbances of lower limb (pain, paresthesias, and rigidity); and abnormal hand posture (extension of wrist and finger joints, except flexion in metacarpophalangeal joint). Condition is associated with cases of epidemic encephalitis, but cause is unknown. Putamen shows reduction of cells and neuroglial overgrowth. Death occurs within 1 year.