Encephalitis and Parkinsonism

VON ECONOMO'S disease (encephalitis lethargica or type A encephalitis) occurred chiefly in the period 1919-1926, and its incidence diminished rapidly thereafter. It continues to be of interest today because of the unusual and remarkable sequelae—the parkinsonian syndrome—which sooner or later appeared in many of its survivors. This syndrome was as likely to appear in a mild as in a severe case of encephalitis lethargica, could develop after a latent period of apparent recovery extending for several years or more, and might even appear in persons who had never had an overt attack of encephalitis. In contrast to paralysis agitans, postencephalitic parkinsonism most often appeared in the second and third decade of life, and contemporary clinicians of the time were struck by the number of children and young adults affected. Wilson noted that "in preepidemic days juvenile paralysis agitans was an absolute rarity but now is commonplace."1Moreover, there