Abstract
Introduction . To study whether voltage topographic analysis of interictal epileptiform discharges (IEDs) in temporal lobe epilepsy (TLE) help to predict the type of scalp ictal onset pattern. Methods . IEDs from 74 patients with drug resistant TLE and unilateral mesial temporal sclerosis (MTS) who underwent presurgical evaluation were categorized according to dipolar fields into Types A and B temporal IEDs. Type A IEDs were defined as those with dipolar fields (tangential/ vertical) with sharply defined negativity over the infero-lateral temporal scalp and positivity over contra lateral centro-parietal scalp. Type B IEDs included all other IEDs other than Type A. Scalp ictal electrographic patterns were classified into rhythms confined to temporal lobe ipsilateral to MTS (“focal”), lateralized to the hemisphere (“regional”), and diffuse, nonlateralized and non-localized rhythms (“diffuse”) and ictal onset to the contra lateral side of MTS (“discordant”). Results . A total of 5476 IEDs and 377 seizures were analyzed. They were divided into four categories based on the side of MTS: 1) Type A IEDs ipsilateral to MTS (44 patients); 2) bilateral Type A IEDs (16 patients); 3) Type B IEDs ipsilateral and Type A IEDs contra laterally (7 patients); 4) Bilateral type B IEDs (7 patients). In 51 of 60 (85%) patients with Type A IEDs (either ipsilateral and/or bilateral to MTS), the ictal pattern was either focal or regional and only in 9 patients (15%) it was “diffuse”.12 of 14 (86%) patients with either ipsilateral or bilateral Type B IEDs showed a diffuse ictal onset, whereas 2 (14%) showed a contralateral ictal onset. Conclusion . In MTS, Type A IEDs are associated with clearly localized ictal onset and Type B IEDs with diffuse ictal onset. A spikevoltage topographic analysis is sufficient for selection of cases for antero-medial temporal lobe resection. Additional home-video recordings of seizures can rule out psychogenic non-epileptiform events.
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