Encephalitis lethargica is also known as or subsumes Epidemic encephalitis and von Economo disease. -ed.
Encephalitis lethargica was a mysterious epidemic disease of the 1920s and 1930s that was better known as the “sleepy” or “sleeping” sickness. It is associated with the subsequent development of postencephalitic parkinsonism, a condition that was popularized in Oliver Sacks’ 1973 book, Awakenings, and the 1990 movie of the same name. Encephalitis lethargica evolved to have many manifestations other than a “lethargic type” including types that were primarily characterized by insomnia and/or movement disorders. Differentiating points from idiopathic Parkinson disease include young age of onset, oculogyric crises, altered sleep-wake cycle, respiratory disturbances, and pyramidal signs. Pathologically, there is diffuse involvement of gray matter of the brain dominantly, the diencephalon, and the mesencephalon. Controversy remains over whether encephalitis lethargica was caused by the influenza virus. No definite treatment is available. Prognosis is variable. In some patients extrapyramidal sequelae persist life-long.