The Elusive Lessons of Encephalitis Lethargica

Encephalitis Lethargica (EL) is a disease that presented as a global pandemic during the early 20th century. It is believed that EL was responsible for the deaths of hundreds of thousands of people, with the remaining one third of survivors left permanently disabled. EL has a high level of morbidity and can cause considerable damage to the central nervous system. While a large outbreak of EL has not occurred in over 100 years, sporadic cases still occur. The etiology and pathogenesis of EL remain unknown. What is known is that EL has two forms, dyskinetic and Parkinsonian. Both forms of EL have similar clinical manifestations, but often differ in the affected patient populations. The dyskinetic form of EL is more common among children, while the Parkinsonian form of EL typically affects adults. Researchers have been attempting to find a connection between influenza and EL as both presented as temporally overlapping pandemics in the early 20th century. Furthermore, a connection between COVID-19 and EL may exist. This is important because both EL and COVID-19 are linked to neurological degeneration. EL has few effective treatments, such as Levodopa, a drug commonly used to treat Parkinson’s disease. The current lack of understanding of EL creates a vulnerability should the condition reemerge in pandemic proportions. If EL is associated with viral infections, then another viral pandemic may be sufficient for EL to return.