P2.264: When to Tap: Complex Febrile Seizure with Atypical Course as Early Presentation of HSV-1 Meningoencephalitis

Introduction: Febrile seizures have a prevalence of 2-5% among children ages 6-60 months. Less than 1% of complex febrile seizures without meningeal signs are associated with bacterial or viral meningitis. Current literature supports limiting routine lumbar puncture in this population. We present a case of Herpes Simplex Virus (HSV) encephalitis presenting with complex febrile seizure, who progressed to cerebritis requiring decompressive craniectomy, and discuss indications for further diagnostic evaluation.

Case Description: 2-year-old male with a history of simple febrile seizure presenting with a 10 minute tonic-clonic seizure with right-sided gaze deviation. He had tactile fever and low energy at home on round-the-clock antipyretics. Afebrile and tachycardic at presentation, no meningeal signs. A non-contrast head CT was negative for intracranial pathology. A second seizure lasting 15 minutes required abortive medications and Neurology was consulted. EEG negative for seizure activity, though given atypical prolonged nature of the febrile seizures, an MRI brain was ordered inpatient. Had persistent high fevers to 40.2°C, and maintenance antiepileptics were started after recurrent seizure activity. On day three of admission, mental status deteriorated with regression in behaviors. MRI demonstrated T2 FLAIR hyperintensities involving the right temporal lobe and insula, suggesting herpes encephalitis. Empiric IV Acyclovir was started, lumbar puncture (LP) was performed and cerebrospinal fluid (CSF) returned positive for HSV-1 and HHV-6 on PCR, mononuclear inflammatory infiltrate, and negative cultures. HSV-1 IgG was positive, concerning for reactivation of a prior HSV infection.

Following initiation of acyclovir, fevers and seizures resolved , however, he quickly became encephalopathic. A repeat head CT showed cerebral edema with a 7mm midline shift, cerebritis in the right cerebral hemisphere and temporal lobe, and tentorial hemorrhage in the right middle cranial fossa, which required decompressive right hemicraniectomy. On completion of 21 days IV acyclovir therapy, repeat LP showed negative HSV-1 PCR. He was discharged on 6 months prophylactic oral acyclovir, with close follow-up with Infectious Disease, Neurology, and Neurosurgery.

Discussion: Current clinical guidelines do not recommend routine lumbar puncture for all children with complex febrile seizures; escalation of treatment with LP and neuroimaging depends on the clinical picture.

Age, history, and absent meningeal signs suggested febrile seizure initially. Negative head CT and EEG may have been falsely reassuring. Concerning clinical findings that triggered further diagnostic evaluation included recurrence of seizures despite antiepileptics, progressive altered mental status, and persistent fever. IV acyclovir should be initiated without delay for suspected HSV encephalitis, while obtaining confirmatory HSV-PCR on CSF.

Conclusion: HSV-1 meningoencephalitis may lead to devastating outcomes and should be considered when encountering complex febrile seizures with an atypical course. History of febrile seizure may act as a red herring and lead to delays in lumbar puncture and imaging; escalation of care should be pursued early to limit disability and mortality.