[P1-40] A Case of Mild Limbic Encephalitis Associated with Influenza Type A
Delirious behavior associated with influenza usually has an onset within a few days after fever and lasts <24 hours. We report on a 12 year-old boy with late-onset and long-standing delirious behavior associated with influenza type A. He was admitted to our hospital because of mild drowsiness with delirious behavior (emotional changes, impulsive behavior, incoherent speech, unresponsiveness) lasting >24 hours. Before admission, he had fever lasted for 4 days. He was diagnosed as influenza A on the second day of fever, and had been treated with laninamivir octanoate hydrate. Delirious behavior occurred after alleviation of fever. Brain MRI, electroencephalography and cerebrospinal fluid analysis was normal. The case fulfilled the diagnostic criteria for influenza encephalitis. He was treated with intravenous methylprednisolone pulse therapy (1 g/day, 3 days). His consciousness was improved after the first day of the therapy, but delirious behavior lasted for 8 days. The brain single photon emission computed tomography (SPECT) showed decreased cerebral blood flow in the bilateral limbic areas. After a month, he recovered without neurologic sequelae. Since his delirious behavior was late-onset and long-standing in contrast to usual influenza encephalitis, immunological mechanisms are suspected.