Introduction: West Nile virus is an asymptomatic infection in most cases, but it can present with a rare complication of deadly neuroinvasive disease.
Case presentation: A 81-year-old White man presented with altered mental status and fever of unknown origin. After extensive workup, he was diagnosed with West Nile encephalitis based on positive serology, lumbar puncture, and clinical presentation.
Discussion: West Nile virus is a mosquito-borne RNA arbovirus that, in rare cases, can lead to encephalitis, which is a challenging diagnosis. There is no current treatment; however, a 5-day course of intravenous immunoglobulin seemed to show acute clinical improvement in both mentation and magnetic resonance imaging of the head and no long-term effects.
Conclusion: We report this case to increase awareness among clinicians to include West Nile virus in the differential diagnosis of encephalitis with fever of unknown origin, particularly in endemic areas.
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