Delayed onset encephalopathy associated with influenza A virus infection

We report three cases of influenza A virus-related encephalopathy developing after the symptoms of influenza improved. The patients' high fever remitted within several days, and other symptoms of influenza also subsided. About that time frequent seizures and disturbed consciousness developed. Brain computerized tomography or magnetic resonance imaging confirmed edema in the whole right hemisphere, bilateral frontal region or the right frontal and occipital areas. All three patients returned to normal neurologic status within 1 to 2 weeks. Influenza A/H3N2 virus infection was confirmed by virus isolation, antigen detection and/or serology. This delayed onset encephalopathy may be explained by a secondary vasculitis caused by immunopathologic reactions.