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 or movement disorders. Because of the lack of a pathognomonic sign, diagnosis of the disease was often uncertain, and the disease was probably overreported. No cause for encephalitis lethargica has ever been determined although a linkage to the approximately contemporaneous so-called “Spanish” (bird-based) influenza epidemic cannot be excluded. Thus, a recurrence of encephalitis lethargica is a possible complication of an H1N1 influenza epidemic.