Case Presentation: Ms. HN is a 29-year-old female with past medical history of hypothyroidism and rheumatoid arthritis managed with sulfasalazine who presented with a chief complaint of confusion. Due to her encephalopathy, history was obtained from her family. She had returned from a trip to Hawaii two days prior to presentation. The patient suffered from headaches, chills, myalgias, cough, sinus pressure, and malaise. She also exhibited paranoia and bizarre behavior. Family reported that she had performed a home viral test that resulted positive for influenza.Physical exam showed a young woman in distress. She appeared agitated and confused. She was alert but not able to effectively communicate. She was repeating a few sentences, for example “it’s paranoia”. She was constantly moving around and appeared restless. She was placed in restraints, from which she was able to remove herself. She was not combative. Vital signs were stable except tachycardia.Initial studies including comprehensive metabolic panel and complete blood count, chest X-ray, and CT of the head showed no abnormalities.MRI of the brain showed two hyperintense lesions of the cerebral white matter that were nonenhancing on FLAIR sequence. Cerebrospinal fluid analysis showed glucose 99 mg/dL, protein 25 mg/dL, and 1-2 nucleated cells/uL.Extended testing of the CSF and serum were negative for Dengue fever, SARS-CoV-2, VZV, HSV, and HIV. CSF encephalitis pathogen panel and autoimmune encephalopathy panel were negative. Nasal swab was positive for influenza A. CSF testing for influenza was not performed.She was treated with oseltamivir and provided with supportive care which led to significantimprovement. She was discharged in stable condition with encephalopathy completely resolved.She followed up in neuroimmunology clinic months later, where retrospective consideration for a post- infectious autoimmune process versus direct infection was made. The patient has returned to her usual activities of daily living.
Discussion: Influenza-associated encephalitis (IAE) is the most likely diagnosis for this patient. While influenza is a common cause of encephalitis in children, it is a rare culprit in adults. IAE lacks a distinct clinical presentation in the adult population, thereby making it a challenging diagnosis.The most common symptoms of IAE are confusion and seizures with less common symptoms including headache and agitation. MRI imaging is variable, but those with abnormalities have a worse prognosis.Treatment typically includes oseltamivir, but this is of uncertain benefit given the unclear mechanism of encephalopathy in influenza infection and the low penetrance of oseltamivir into the CSF. Other proposed treatments, such as glucocorticoids, are also of unclear benefit.
Conclusions: Nervous system involvement is rare but may occur following an influenza infection. Influenza and its complications should be on the differential diagnosis for encephalopathy.In this patient with confusion, agitation, and symptoms of upper respiratory infection, a diagnosis of influenza- associated encephalitis was made. After treatment with oseltamivir and supportive care, she made a full recovery.This case highlights the role of hospital medicine in history-gathering, diagnosis, and treatment of an uncommon manifestation of a common disease.