Characteristic early electroencephalographic changes in herpes simplex encephalitis.

We review electroencephalograms taken from 17 patients with severe meningoencephalitis within seven days of onset of CNS symptoms and prior to cortical brain biopsies. All patients had CNS disease clinically compatible with the diagnosis of herpes simplex encephalitis (HSE). The diagnosis was demonstrated by the isolation of virus from the brain in five patients (group 1) but considered highly unlikely in the other 12 patients (group 2) by negative immunofluorescent studies and failure of viral isolation from the brain tissue. Abnormal but nonspecific EEGs with diffuse or focal slowing were found in all patients. Distinctive high-voltage, 1-cycle-per-2-to-3 seconds periodic sharp waves from unilateral temporal lobes were seen only in three of the five patients with virologically proved HSE but in none of the 12 patients without viral isolation. This EEG pattern is strikingly similar in all three patients, regardless of their age, and may be specific for the early diagnosis of HSE prior to brain biopsy. The EEGs of the other two patients with proved HSE did not contain such abnormalities. Athough periodic EEGs with some resemblance to those previously described may occur in other CNS disorders, their presence strongly suggests the diagnosis of HSE when recorded from patients with viral meningoencephalitis. Moreover, EEGs may help locate the best site for cerebral biopsy since maximal yield of the virus in this study was from unilateral temperoal lobes corresponding with the site of local EEG changes.