Neuropathological findings in West Nile virus encephalitis: a case report.

A 67-year-old woman had fever, myalgias, progressive weakness, and respiratory insufficiency. In 9 days, flaccid areflexic quadriparesis and bulbar palsy developed. She died 26 days after the onset of her illness. Serum and cerebrospinal fluid serology were positive for West Nile virus. Neuropathological study showed changes consistent with a viral encephalomyelitis, similar to poliomyelitis. The brainstem showed neuronal loss and multiple foci of necrosis. The spinal cord showed severe loss of anterior and posterior horn neurons. Immunohistochemistry identified West Nile virus antigens in the brainstem and spinal cord. Paralysis, in West Nile virus encephalitis, is caused by destruction of motor neurons.