Parkinsonism following encephalitis of unknown etiology.

The patient, a clinical case of parkinsonism, was a 32-year-old man, born in 1942, long after the prevalence of von Economo's lethargic encephalitis in Japan. Anatomically, the neurons in the substantia nigra of the mid-brain were extensively degenerated, and presented Alzheimer's neurofibrillary tangles. At the same time, melanin pigment was scattered in the tissue and was phagocytized by glia cells. Perivascular cuffing was observed in the frontal lobe, parietal lobe, temporal lobe, hippocampus, and thalamus as well as in the substantia nigra. Neuronophagia was noted in the thalamic nuclei. The present case was believed to have parkinsonism not clinically or pathologically related to von Economo's encephalitis or to Japanese encephalitis, but following a mild encephalitis of unknown etiology.