Herpes Simplex Encephalitis Without CSF Leukocytosis

Herpes simplex encephalitis (HSE) is the most common cause of sporadic acute necrotizing encephalitis in temperate climates.1-3Untreated, its mortality ranges from 51% to 80% and there is often significant neurologic morbidity among survivors.4,5Early treatment with vidarabine may reduce mortality to approximately 25%6,7Herpes simplex encephalitis is diagnosed with a combination of clinical findings, laboratory data such as CSF examination, computed tomographic (CT) scan and EEG, and, now, in a majority of cases, brain biopsy.8Typical symptoms include acute febrile encephalopathy with headache, alteration of consciousness, behavioral changes, convulsive seizures, dysphasia, and hemiparesis. While no combination of clinical findings definitely distinguishes HSE from other viral encephalitides,9the occurrence of focal neurologic signs in patients with encephalitis immediately suggests the diagnosis. Focal disruption of the blood-brain barrier as demonstrated by CT or radionuclide brain scanning has been reported to occur early in HSE,10,11