Encephalitis lethargica ('sleeping sickness') was a mysterious disorder that swept the world in the decade following the First World War, before disappearing without its cause having been identified. Around 85% of its victims, predominantly children, adolescents and younger adults, survived the acute disorder, but most developed severe neurological syndromes, particularly severe post-encephalitic parkinsonism and other severe motor abnormalities, that incapacitated them for the remainder of their lives.
Despite its brief history, encephalitis lethargica played a major role in a variety...