Delayed onset of post-rabies vaccination encephalitis.

A 31-year-old veterinarian developed seizures, left hemiparesis, loss of memory, and behavioral disorders 5 months after intensive antirabies vaccination, the longest incubation period yet recorded. Computed tomographic scan revealed a right frontal contrastenhanced mass that extended to the left frontal lobe through the corpus callosum. Brain biopsy showed foci of primary demyelination largely confined to the white matter. The lesions were characteristic of the demyelinating encephalomyelitis that follows treatment with certain vaccines against rabies. The hemiplegia improved, but seizures, memory impairment, and abnormal behavior persisted.