Encephalitis lethargica

Historical note and nomenclature
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By Joel A Vilensky PhD

On April 17, 1917, at a meeting of the Vienna Society for Psychiatry and Neurology, Dr. Constantin von Economo described a new disease, encephalitis lethargica (von Economo 1931). Shortly thereafter, von Economo published his first article on the disease (von Economo 1917). He described a series of cases in which the patients exhibited “a kind of sleeping sickness” with an unusually prolonged course. Headache and malaise were the first symptoms followed by somnolence often associated with delirium, from which the patient could be easily awakened. This state could rapidly lead to death or could persist for long periods, either progressing to coma or ending with recovery. These signs were generally accompanied by paralysis in some of the cranial nerves, especially those affecting the eye. Ptosis was a typical sign. Von Economo concluded that he believed the disease was an “encephalitis,” with the variability relating to variations in neural localization of the causative agent.

The disease then began appearing in increasing frequency throughout the world, with official figures showing peaks of about 10,000 cases in 1920 and 1924 (Neal 1929), with a possible total mortality of 500,000 cases (Ravenholt and Foege 1982) during the entire epidemic period, which lasted until about 1940. Sporadic reports of encephalitis lethargica cases have continued to appear since then.

During the epidemic period, the signs and symptoms of the disease rapidly increased so that eventually 28 “types” had been described, with signs and symptoms encompassing virtually every neurologic system (Vilensky and Gilman 2006), including some that were antithetical to von Economo’s original description (eg, an “insomnia” type). Kroker convincingly argued that curing encephalitis lethargica became the foremost aim of American neurology (especially New York City neurologists) during this period, and that the secondary goal of this effort was to increase significantly the prominence and potential of American neurology (Kroker 2004). Thus, there may have been some political aspects to the large number of encephalitis lethargica diagnoses. This possible overdiagnosis was also noted during the epidemic period (Ford 1937).