The sequential EEGs of 15 neonates with herpes simplex virus meningoencephalitis were correlated with clinical and laboratory findings at the Children's Hospital, Harvard Medical School, and Massachusetts General Hospital, Boston, MA. EEGs were abnormal in seven (88%) of eight neonates examined during days one to four of the illness and three (38%) showed a multifocal periodic pattern. In three patients with an early abnormal EEG the CT and ultrasound were normal. All patients examined during days five to 11 of the illness had abnormal EEGs and three had multifocal periodic patterns. Nine patients with severe neurologic sequelae and vegetative state examined after day 11 of the illness showed markedly abnormal EEGs with very low voltage or electrocerebral silence. The authors concluded that the EEG is a sensitive test that may be superior to radiologic procedures in the early diagnosis of neonatal herpes simplex encephalitis. The multifocal periodic pattern in the presence of CSF pleocytosis is highly suggestive of the diagnosis. 
COMMENT. The cranial CT and ultrasound studies may be normal when the EEG is abnormal during the first few days of neonatal herpes encephalitis. An MRI with T2 weighted images may be more revealing than the CT and will show multiple small disseminated lesions.