Neurophysiological studies in herpes simplex encephalitis

In herpes simplex encephalitis (HSE), simultaneous electro-encephalogram (EEG) and evoked potential studies have not been reported, although EEG changes have been described. In this communication, EEG, somatosensory and motor evoked potentials have been reported in 9 patients with HSE. The patients' age ranged between 2 and 70 years and 3 were females. Seven patients had seizures, CT scan was abnormal in 6 and MRI in remaining 3 patients. Seven patients received acyclovir therapy; one patient died and 6 had poor outcome. The initial EEG was carried out within 5 days of ictus and was abnormal in all the patients. The EEG abnormalities included frontotemporal delta slowing in 5, periodic lateralised epileptiform discharge in 3, runs of spike and periodic activity in one patient each. At 3 months, EEG was normal in 6 patients but it did not correlate with clinical recovery. Central motor conduction time (CMCT) to upper limb and median somatosensory evoked potential (SEP) were normal in all. CMCT to lower limbs and tibial SEPs were unrecordable in one patient who had wide spread herpes simplex virus (HSV-1) infection associated with AIDS, and died on 18th day of illness. From this study, we conclude that EEG although is frequently abnormal and may provide useful diagnostic information in a setting of encephalitis but evoked potential changes are infrequent; and if present an association of HIV infection should be considered.