Correlations between EEG changes induced by diazepam and the localization of epileptic spikes and seizures

We evaluated the EEG reaction to an intravenous injection of diazepam as an additional tool in difficult localization problems in epilepsy. The normal reaction to diazepam being an increase in beta activity, it was assumed that a poor increase indicated an abnormal region. This method was tested in 21 epileptic patients having chronically implanted intracerebral electrodes. Beta activity before and after injection was quantified by spectral analysis; increases were compared in homologous contralateral channels. In 12 of the 21 cases the area of poorest response to diazepam was identical to that of seizure onset. In 7 cases, there was some overlap between the area of poorest diazepam response and that of seizure onset, but they did not exactly coincide. In two cases there was no overlap between the two areas. Agreement was slightly higher when comparing diazepam response and area of highest interictal spike activity. This procedure is simple and without risk, particularly compared to the thiopental injection which is used for the same purpose. It is helpful in determining abnormal areas when localization information from various diagnostic sources are conflicting. Even when the epileptic focus is well defined, it can point to other poorly functioning areas.