Encephalitis lethargica and narcolepsy have more in common than just sleepiness, reports Oxford University Press’s blog.

Von Economo hypothesized that infection with influenza might predispose a person to infection with encephalitis lethargica by increasing the permeability of the mucous membranes. The concept of autoimmunity was not discovered until the 1950s. Since then, a few hypotheses have pointed to an autoimmune mechanism as the cause of encephalitis lethargica.