There are numerous recorded instances in which the old rabies vaccine (with neural tissue) induced an attack of what subsequently appeared to be MS. Shiraki and Otani reported such examples from Japan. The evolution of symptoms was subacute, over a period of 2 to 4 weeks, and the demyelinating lesions were macroscopic—up to 1 to 2.0 cm in diameter—but composed of confluent perivenous lesions. The disease could be reproduced in dogs—persuasive evidence that one form of acute MS is a variant of ADEM. Encephalomyelitis following vaccination against smallpox has been known since 1860, having occurred about once in 4,000 vaccinations. That disease is now of historical interest only, insofar as smallpox has disappeared as a human illness.
The temporal association of the neurologic disorder with vaccination supports the diagnosis and the characteristic combination of encephalitic and myelitic features will help to distinguish the condition from meningitis, viral encephalitis, and poliomyelitis. Rarely, an atypical case may mimic any one of these disorders. On occasion, the disease may suggest involvement of nerve roots and peripheral nerves and resemble acute inflammatory polyneuritis (Guillain-Barré syndrome). In fact, the rabies vaccine produced in South America from suckling mouse brain causes this type of peripheral nerve disease more often than encephalomyelitis.
Mundane inoculations such as those for influenza or hepatitis must have a very small rate of ADEM, judging from surveillance studies; Ascherio and colleagues were unable to find any increase in cases among 2 large studies of nurses who received hepatitis B vaccine. The absence of a clear connection of MS to vaccination has already been mentioned.
The mortality rate of postvaccinal encephalomyelitis  had in the past been high, between 30 and 50 percent. If recovery occurs, it may be surprisingly complete. However, a significant proportion of patients show residual neurologic signs, mainly in the form of seizures, intellectual impairment, or behavioral abnormalities.
Corticosteroids given soon after the appearance of neurologic signs may modify the severity of experimental allergic encephalomyelitis; this provides the logic for their use in the human counterpart of this disease but controlled trials have not been carried out. We usually administer methylprednisolone in high doses intravenously for 3 to 5 days. Plasma exchange and intravenous immune globulin have also been apparently successful in some fulminant cases (Kanter et al; Stricker et al) but it is difficult to affirm this.
Acute Necrotizing Hemorrhagic Encephalomyelitis (Acute Hemorrhagic Leukoencephalitis of Weston Hurst)