Epidemics of encephalitis lethargica (EL), from 1917 to the 1930s, are an important milestone in the history of movement disorders. Today, the two best-known features of EL are somnolence and parkinsonism but the full clinical picture was variable and complex. States of wakeful inactivity—as opposed to drowsiness—were often described both in the acute and postacute stages and were referred to in the EL literature as “lethargy” or “torpor.” The study described here is based on a survey of clinical descriptions published in English, French, and German from 1917 to 1942. Its focus is on the history of clinical ideas, rather than applying modern pathophysiological concepts retrospectively. Descriptions of lethargy are explored as a way of elucidating concepts of sleep, fatigue, and motivation during the study period.
The literature described many patients who had (1) lethargy without interruption in consciousness; (2) slowness of movement and catalepsy without other prominent parkinsonian features; and (3) apathy and lack of initiative without severe disorders of mood or thought content. Hence observers distinguished a state of wakeful inactivity from primary disorders of sleep, movement and behavior.
Contemporaneous accounts suggest that writers had difficulty in reconciling their observations with preexisting concepts; there still may be limitations in our ability to describe and classify the clinical states connected during the epidemic era with the term “lethargy.” © 2011 Movement Disorder Society