H1N1 Encephalitis with Malignant Edema and Review of Neurologic Complications from Influenza

BACKGROUND: Influenza virus infection of the respiratory tract is associated with a range of neurologic complications. The emergence of 2009 pandemic influenza A (H1N1) virus has been linked to neurological complications, including encephalopathy and encephalitis. METHODS: Case report and literature review. RESULTS: We reviewed case management of a 20-year old Hispanic male who developed febrile upper respiratory tract signs and symptoms followed by a confusional state. He had rapid neurologic decline and his clinical course was complicated by refractory seizures and malignant brain edema. He was managed with oseltamavir and peramavir, corticosteroids, intravenous gamma globulin treatment, anticonvulsants, intracranial pressure management with external ventricular drain placement, hyperosmolar therapy, sedation, and mechanical ventilation. Reverse transcriptase polymerase chain reaction analysis of nasal secretions confirmed 2009 H1N1 virus infection; cerebrospinal fluid (CSF) was negative for 2009 H1N1 viral RNA. Follow-up imaging demonstrated improvement in brain edema but restricted diffusion in the basal ganglia. We provide a review of the clinical spectrum of neurologic complications of seasonal influenza and 2009 H1N1, and current approaches towards managing these complications. CONCLUSIONS: 2009 H1N1-associated acute encephalitis and encephalopathy appear to be variable in severity, including a subset of patients with a malignant clinical course complicated by high morbidity and mortality. Since the H1N1 influenza virus has not been detected in the CSF or brain tissue in patients with this diagnosis, the emerging view is that the host immune response plays a key role in pathogenesis.