The link between viral infection, the brain, and fatiguing illnesses has a long history. This combination forced itself on the medical imagination after events in Austria in the winter of 1916-17. A virulent form of influenza was noted, characteristically, to produce lethargy and later, to leave a host of neurological deficits in its wake. By the spring of 1918 several English cases of encephalitis lethargica had been reported and in the next year the disease was notifiable. The peak of the epidemic occurred in 1924 in the United Kingdom, at which time the Board of Control reported that many cases had been admitted to hospital with psychiatric disturbances.1 Hence the notion that apparent psychiatric illnesses may be misdiagnosed manifestations of a postinfectious cerebral disease began; it refuses to disappear.23
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Source: Cope H, David AS. Neuroimaging in chronic fatigue syndrome. J Neurol Neurosurg Psychiatry. 1996 May;60(5):471-3. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC486356/