Abstracts

Rationale: Temporal intermittent rhythmic delta activity (TIRDA) is an EEG pattern characterized by sinusoidal trains of activity, ranging from 1 to 3.5 Hz, localized over the temporal regions [1]. This activity has been described in 30 to 90% of patients with temporal lobe epilepsy (TLE) [2]. IT has been shown that TIRDA has the same lateralization of epileptiform abnormalities in patient with TLE [3]. Several studies have tried to understand the localizing value of this rhythm and its association with surgical outcome. Much debate exists in the literature regarding the exact localizing value of TIRDA: mesial vs neocortical. Our previous study has shown how this pattern is associated with neocortical temporal lobe epilepsy (NTLE)[4]. However, depth hippocampal electrodes were lacking in our study. With this study we aim to confirm the results of the previous one, by analyzing the presence of TIRDA in 2 patients with temporal lobe epilepsy and depth electrodes in the hippocampus and in the lateral temporal lobe.Methods: The occurrence of TIRDA was investigated by means of simultaneous scalp and intracranial EEG recordings in 2 patients affected by right temporal lobe epilepsy. Both patients had hippocampal depth electrodes and 3 lateral temporal depth electrodes, covering anterior, mid and posterior neocortex.Results: Interictal epileptiform discharges were recorded over the right hippocampal and lateral temporal depth electrodes. Both patients had seizures with right mesial temporal onset. TIRDA was observed over the lateral temporal electrodes and was not observed concomitantly over the hippocampal electrode (Fig. 1). TIRDA was not associated with seizure onset (Fig. 2).Conclusions: Our findings show that TIRDA is associated with temporal neocortex and is not associated with the seizure onset zone in patient with mesial temporal lobe epilepsy. These findings suggest that TIRDA might be a marker of a more extensive epileptic network that involves also the neocortex in patients with MTLE. This finding may have important implications for surgical outcomes.