Herpes simplex virus encephalitis following acute brain injury: illustrative cases.

BACKGROUND: Herpes simplex virus (HSV) is the most common cause of sporadic viral encephalitis in adults, yet HSV encephalitis (HSVE) occurrence in the setting of traumatic brain injury (TBI) and intracranial hemorrhage (ICH) is rarely documented. Brain injury induces systemic immunosuppression that may predispose to viral reactivation. Neurological deterioration in these patients is often attributed to the primary injury, which may delay recognition of superimposed viral encephalitis. OBSERVATIONS: The authors present 3 cases of HSVE following neurological injury: a 68-year-old woman with a spontaneous thalamic ICH, a 36-year-old man with TBI requiring craniotomy, and an 80-year-old man with nonaneurysmal subarachnoid hemorrhage. Acyclovir treatment was initiated for all based on clinical suspicion and pending BioFire FilmArray Meningitis/Encephalitis Panel (MEP) results, but 2 patients died due to irreversible neurological damage and significant comorbidities. LESSONS: HSVE should be considered in patients with unexplained or disproportionate neurological deterioration after acute brain injury, even when the primary injury provides an apparent explanation for encephalopathy. New temporal, insular, or orbitofrontal abnormalities on MRI; refractory seizures; persistent fever; or clinical decline despite stable structural imaging should prompt early MEP testing and empiric acyclovir therapy while results are pending. https://thejns.org/doi/10.3171/CASE26525.