Influenza-Associated Encephalitis in an Adult Patient: A Case Report

Case Diagnosis: 76 year old male with Influenza-Associated Encephalitis (IAE)

Case Description or Program Description: Patient is a 76 year old male with no prior psychiatric history who presented to the emergency room for visual and auditory hallucinations. Specifically, he reported interacting with individuals known to be deceased. He was experiencing additional cognitive deficits related to memory, orientation, and processing speed. He also had 2-3 days of cough, fatigue, and diarrhea. CT Head revealed no acute process, but did show chronic bilateral lacunar infarcts. Drug screening was negative for any recent substance use. Lumbar puncture revealed a negative meningitis panel and an electroencephalogram was negative for seizures. Due to his generalized flu-like symptoms, a respiratory viral swab was obtained and was positive for influenza A. He was subsequently treated with oseltamivir, intravenous (IV) steroids and IV immune globulin for suspected IAE.

Setting: Acute Rehabilitation Hospital

Assessment/Results: The patient was stabilized and admitted to an acute rehabilitation facility, where significant neurologic improvements were seen within 1-2 weeks with regards to his orientation, attention, concentration and memory. He remained medically stable and was successfully discharged home with outpatient therapy.

Discussion (relevance): The incidence of neurologic sequelae associated with influenza is highest among children, specifically ages less than 5 years. These include mental status changes, lethargy, seizures, and even coma. Due to its lower incidence, the general understanding of IAE among adults is limited and cases may be misdiagnosed. This is important to consider because mortality from IAE increases with age due to many factors including decreased immune response and increased likelihood of medical comorbidities.

Conclusions: While the pathophysiology of IAE is not fully understood and it remains a rare phenomenon among adults, IAE should remain on the differential diagnosis when influenza-like symptoms are present and when encephalopathy is suspected. Prompt diagnosis and treatment is crucial to prevent increased morbidity and mortality in this population.