HHV-6 Encephalitis in an Immunocompetent Child: A Steroid-Responsive Case Complicated by Cerebral Venous Sinus Thrombosis.

An 11-year-old male presented with bifrontal headaches that were initially brief and infrequent but progressed to up to 12 episodes daily, associated with photophobia, left eye twitching, and bilateral eye redness. Initial evaluation revealed leukocytosis with normal head CT findings; however, his condition rapidly progressed to refractory seizures. Brain MRI demonstrated increased signal in the left medial temporal lobe, and EEG showed focal spikes and waves in the left hemisphere, consistent with focal epilepsy. Cerebrospinal fluid and serum PCR testing were positive for HHV-6. Despite treatment with anti-epileptics and intravenous immunoglobulin(IVIG), his mental status declined, and repeat MRI revealed cerebral venous sinus thrombosis. Extensive testing was negative. Marked clinical improvement occurred only after corticosteroid initiation. This case highlights a rare presentation of HHV-6-associated encephalitis in an immunocompetent child complicated by status epilepticus and cerebral venous sinus thrombosis, suggesting an immune-mediated mechanism.