The etiology of parkinsonism remains as much an enigma today as it was 150 years ago when the syndrome was first fully defined. Although many disease processes have been implicated, none has received more attention than encephalitis and particularly encephalitis lethargica. Since the last epidemic of encephalitis lethargica subsided 40 years ago, it seems pertinent to inquire what proportion of parkinsonian patients seen today represent its sequelae, and whether other types of encephalitis can cause parkinsonism as is sometimes alleged. Clinical and epidemiological evidence bearing on these questions is reviewed in the March issue of the Archives of Neurology.1
Encephalitis lethargica was the first type of epidemic encephalitis to be recognized; indeed, for some years the two terms were synonymous. Initially, it was thought, along with multiple sclerosis and poliomyelitis, to be part of the "epidemic constitution of influenza," a view which gave rise to a long-persisting confusion regarding