Demyelinating diseases of the CNS can be categorized into disseminated and focal lesions. Acute disseminated encephalomyelitis (ADEM) is characterized by acute depression of consciousness and multifocal neurologic findings occurring within days to weeks (5 days to 6 weeks) following an inciting event. It is characterized pathologically by diffuse foci of perivenular inflammation and demyelination most prominent in the white matter of the brain and spinal cord (Johnson et al., 1985). Optic neuritis and transverse myelitis are focal demyelinating lesions that can occur in isolation or as components of diffuse demyelinating diseases such as ADEM and multiple sclerosis. Transverse myelitis is characterized by the acute onset of signs of spinal cord disease, usually involving the descending motor tracts and the ascending sensory fibers, suggesting a lesion at one level of the spinal cord. The annual incidence of transverse myelitis in Rochester, Minnesota, from 1970 to 1980 was 7.4 per 100,000 individuals (Beghi et al., 1982). Optic neuritis represents a lesion in the optic nerve behind the orbit but anterior to the optic chiasm. No population-based incidence rates were identified. For a more complete description of demyelinating diseases of the CNS, see Chapter 3.
Demyelinating disease of the CNS has long been known to follow viral and some bacterial infections and the administration of live attenuated and inactivated antiviral vaccines. Demyelinating complications following vaccination were first noted after the introduction of rabies vaccine grown in animal brain or spinal cord in the 1880s. On rare occasions, encephalomyelitis also complicated the injection of vaccinia virus, which is used for the prevention of smallpox. For a more complete discussion of the history of the suspected association between vaccines and the development of demyelinating lesions of the CSF, see Chapter 3. In the more recent literature, several case reports of ADEM in association with tetanus toxoid have been described (Schlenska, 1977; Schwarz et al., 1988), but there has not been a pathologically proven case of ADEM following administration of tetanus toxoid, DT, DPT, or Td. Case reports of transverse myelitis (Read et al., 1992; Whittle and Roberton, 1977) and optic neuritis (Quast et al., 1979; Topaloglu et al., 1992) have been presented in the literature as well.