Cerebellitis as a Rare Manifestation of HSV Encephalitis: A Case Report

Background: Herpes Simplex Virus (HSV) is a common cause of encephalitis. A feared complication of HSV encephalitis is hemorrhage and necrosis of the brain parenchyma most commonly in the temporal lobe(s). Less common sites of focal necrosis include the insula and inferior frontal lobes. A rare presentation of HSV encephalitis is cerebellitis. Case: A 74-year-old female presented with a 1-month history of progressive balance difficulty and dizziness. The neurological exam showed truncal ataxia and scanning dysarthria. Serum labs were largely unremarkable, except for elevated sedimentation rate (ESR). Brain MRI revealed diffuse cerebellar swelling and T2 signal changes, with left medial enhancement. Cerebrospinal fluid (CSF) analysis showed elevated red blood cells (WBCs 5, RBCs 438, protein 54.7, glucose 64) and was positive for HSV-1 PCR. The CSF autoimmune encephalopathy panel was negative. She was treated with acyclovir 10 mg/kg every 8 hours for 14 days and IV methylprednisolone 1000 mg daily for 5 days, followed by an oral prednisone taper. Clinical improvement in ataxia and dizziness was observed soon after treatment began, with decreased cerebellar edema and enhancement on repeat MRI. After discharge, the patient was lost to follow-up, and long-term neurological status remains unknown. Conclusions: Recognition of atypical HSV encephalitis is crucial as encephalitis has a broad differential and CSF HSV PCR is a widely available and highly specific test. Rapid administration of acyclovir is the current standard of care. Addition of pulse dose methylprednisolone may also impart symptomatic and radiographic benefit.