Acute necrotizing encephalopathy.

Influenza virus infection is a rare cause of neurological complications, with acute necrotizing encephalopathy (ANE) being among the deadliest. Due to the low incidence of ANE, literature about its association with influenza B infection is limited. We present the case of a 29-year-old previously healthy man with an imaging and clinical diagnosis of influenza B virus infection and sudden decline in mental status. Magnetic resonance imaging showed multifocal areas of abnormal T2 FLAIR signal and restricted diffusion without significant enhancement, with negative mircobiological studies of cerebrospinal fluid. The patient died despite multiple treatments including an antiviral, steroids, and intravenous immunoglobulin. Due to ANE's more common presentation during childhood, this case report represents one of the few available publications in the adult population.