Lumbar puncture was performed - herpes simplex virus DNA was not shown on polymerase chain reaction. A brain biopsy was performed and the histology was consistent with encephalitis. PCR was repeated on the biopsy specimen and was positive for HSV type I.

HSV encephalitis typically produces abnormal signal +/- enhancement in the limbic system and temporal lobes. It is usually bilateral but asymmetrical. The basal ganglia are usually spared. The differential diagnoses include limbic encephalitis (paraneoplastic), gliomatosis cerebri, and status epilepticus. HSV-1 causes 95% of all herpetic encephalitides. Mortality ranges from 50-70%, and treatment is with intravenous antivirals.