An Adult Case of Influenza-associated Encephalitis Successfully Treated with High Dose Intravenous Immunoglobulins

A 73-year-old man was admitted to our hospital with a high fever and left paresis. A rapid diagnosis test was positive for influenza A was positive by rapid diagnosis test and diffusion-weighted MRI imaging of the brain showed a high intensity lesion of the right cerebral peduncle. The patient was therefore diagnosed as having influenza A virus infection complicated with lacunar infarction. In spite of initial treatment with oseltamivir and anticoagulant therapy, he lost consciousness eight hours after admission. The high intensity lesion of the cerebral peduncle enlarged and new lesions in the thalamus, hippocampus and calcarine cortex were detected with brain MRI. Additionally, an electroencephalographic study showed an entire slow wave and as the other causative pathogens of central nerve system infection were not detected, the likely diagnosis was influenza-associated encephalitis. We administered a high dose of intravenous immunoglobulin since the low-grade fever and mild unconscious state had continued in spite of the treatment with methylprednisolone pulse therapy. His consciousness was restored and body temperature became normal immediately. We could confirm the efficacy of our treatment by measurement of IL-6 levels in the serum and cerebrospinal fluid during the entire clinical course. In conclusion, a high dose of intravenous immunoglobulin therapy might be one of the effective treatments for influenza-associated encephalitis.