Frequency of bitemporal independent interictal epileptiform discharges in temporal lobe epilepsy

Purpose: Bitemporal interictal epileptiform discharges (IEDs) occur in less than or equal to 42% of scalp EEGs in patients with temporal lobe epilepsy (TLE) studied with routine EEGs or partial analysis of long-term recording s. Methods: Twenty-eight patients with TLE demonstrating exclusively unilatera l temporal IEDs on routine EEGs underwent 24-h continuous recording. The en tire record was visually inspected for epileptiform discharges. We used con tinuous EEG to assess the significance of long-term recording in detecting bilateral IEDs. Results: Twenty-two patients had left temporal IEDs; 21 had right temporal IEDs. Seventeen (61%) patients had IEDs originating from both the right and left temporal lobes. The probability of detecting bilateral independent IE Ds was correlated with the duration of continuous EEG recording. There was no correlation between the number of IEDs originating from one side and the probability of detecting independent IEDs on the other side. The frequenci es of IEDs were not correlated with the length of time since onset of epile psy. Conclusions: The findings suggest that when long-term recordings are perfor med, the incidence of bilateral discharges in TLE is higher than previously reported in the literature and supports the view that TLE is commonly a bi lateral disease.