Simply influenza A (H3N2)-associated encephalitis with seizure

Influenza-associated acute encephalopathy (IAE) is more prevalent in children than in adults and often results in neurological sequelae or even death. Diagnosis of IAE is difficult as clinical presentation varies significantly and the influenza virus is rarely detected in cerebrospinal fluid. Moreover, seizures in adults due to influenza infection are rare. Herein, we describe the case of an adult presenting with both acute encephalitis and seizures. A 38-year-old female was admitted to the emergency department with acute respiratory symptoms and fever, followed by quick progression to stupor within 24 h. A rapid antigen test was influenza A-positive, and polymerase chain reaction of nasal secretions confirmed the H3N2 subtype. Brain magnetic resonance imaging showed bilateral water restriction lesions at the thalamus and the cerebellum and an electroencephalogram showed frequent episodic generalized sharp-and-slow waves over the bilateral frontal region. Based on the neuroimaging and laboratory findings, we diagnosed the patient with adult influenza A (H3N2)-related encephalitis complicated by seizure. Treatment with oseltamivir and anticonvulsants led to complete neurologic recovery by day 14. This report describes two unusual neurological manifestations of influenza A, i.e., encephalitis and seizures, in an adult. We emphasize that, in adults presenting with acute viral encephalitis, clinicians should consider influenza infection as part of the differential diagnosis, and that typical neuroimaging in conjunction with laboratory detection of influenza virus and/or intrathecal antibody production suggestive of IAE, may help establish an accurate diagnosis.