Viral myelitis: an update.

Viral infections of the central nervous system are uncommon but are important in the differential diagnosis of acute myelopathy. Acute viral myelitis can present as acute flaccid paralysis (poliomyelitis) or neurologic dysfunction due to involvement of the white matter. The latter usually affects only part of the transverse expanse of the spinal cord and manifests as asymmetric motor and sensory symptoms. When both halves of the spinal cord are affected, the entity is referred to as acute transverse myelitis and patients exhibit uniformly symmetric weakness, sensory loss, and urinary bladder involvement. Acute flaccid paralysis is due to cytolytic infection of anterior horn cells. When the involvement is mainly white matter, virus-specific and autoimmune host cellular immune responses are believed to contribute to spinal cord damage. Acute flaccid paralysis is caused by polioviruses-1, -2, and -3; coxsackieviruses A and B; enterovirus-71; and flaviviruses, including West Nile virus. Involvement of spinal cord white matter may be associated with infection by many different viruses; however, in most cases a specific viral cause is never determined. Chronic myelitis may be due to either direct infection of the spinal cord by human T-cell lymphotrophic virus-1 (HTLV-1), or a metabolic disturbance due to HIV-1 infection in AIDS patients; no other human virus is known to chronically infect the spinal cord without involvement of the brain. The principal treatment is antiviral drugs immediately upon virus isolation or the identification of a viral sequence by PCR and, when indicated, high doses of methylprednisolone.