Increase awareness of the subtle encephalitic syndrome to prevent misdiagnosis

Herpes Simplex Virus 1(HSV-1) Encephalitis (HSVE) is the most common encephalitis with an annual incidence of 1.2 per 100,000 patients. Infection usually occurs through immediate or reactivated HSV-1 infection despite Immunocompetency. A high index of suspicion is required as diagnosis is confirmed by invasive analysis of cerebrospinal fluid.

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A 71-year-old immunocompetent caucasian male presented as a stroke alert from an outside hospital with an NIH stroke scale of 15 for disorientation and complete left hemiparesis. A head CT revealed a right temporal hypodensity with a 3.5mm midline shift suspicious for malignant ischemic infarction without large vessel occlusion on head and neck CT angiogram. He was outside of the treatment window for alteplase, started on mannitol, and admitted to the Neurosurgical Intensive Care Unit.  Over the next 12 hours, he became febrile to 39.3C. A brain MRI revealed diffusion restriction in the right frontal, temporal and occipital lobe with bilateral hippocampi involvement and electroencephalogram revealed PLEDS in the right occipital region. He was started on empiric intravenous acyclovir for concern for HSVE despite lack of reported previous herpetic infection. Cerebrospinal fluid studies showed 7 RBC, 42 glucose, 141 protein, 103 nucleated cells with 95% lymphocytes and eventual HSV-1 PCR positivity. Patient continued high dose acyclovir treatment for 21 days with persistent cognitive impairment on six-month follow-up.

Stroke mimics are diagnostic challenges to distinguish from classical strokes. HSVE typically presents with neurological deficits, temporal diffusion restriction on neuroimaging, and fever. A high index of suspicion for HSVE is key to diagnosis and early initiation of empiric Acyclovir can profoundly reduce long term disability and mortality from 70% to 7%. Recognizing the telltale signs of HSVE in an afebrile immunocompetent patient as in the case above will help clinicians differentiate stroke mimics.