The incidence of encephalomyelitis in association with acute specific fevers and prophylactic inoculations is discussed. Available statistics are inaccurate, but these conditions are of considerable importance—it is likely that there are about 400 cases of measles encephalitis in England and Wales in an epidemic year.The pathology of these neurological complications is discussed and emphasis placed on the distinction between typical perivenous demyelinating encephalitis, and the toxic type of encephalopathy which occurs mainly in young children.The clinical syndromes occurring in association with measles, chickenpox and German measles are considered. Although encephalitis is the most frequent complication, myelitis and polyradiculitis also occur. There is evidence that ‘uncomplicated measles’ is associated with brain involvement in the prodromal phase. Similar para-infectious disorders occur in association with other infections including smallpox and influenza.The post-vaccinal types of encephalomyelitis are also considered with particular reference to post-vaccinial encephalitis and rabies post-vaccinal encephalitis.The pathogenesis of these disorders is discussed and it is concluded that there is direct viral invasion of the nervous system, followed by an antigen-antibody reaction. At times virus may remain latent within the nerve cell without destroying it.
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