Interictal EEG and ictal scalp EEG propagation are highly predictive of surgical outcome in mesial temporal lobe epilepsy

Purpose: Surgical outcome in patients with mesial temporal lobe sclerosis ( MTS) is worse than that in patients with temporal lobe activity (TLE) with tumors. previous studies of the ictal EEG focused on ictal EEG onset in sca lp EEG or ictal EEG propagation in invasive recordings, Ictal EEG propagati on with scalp electrodes has not been reported. Methods: Ictal scalp EEG propagation patterns were studied in 347 seizures of 58 patients with MTS or nonlesional TLE. Interictal epileptiform dischar ges (IEDs) and the presence of unilateral mesial temporal lobe atrophy in m agnetic resonance imaging (MRI) also were studied in these 58 patients. For ty-nine patients were operated on (minimal follow-up of 1 year). Results: Postoperatively, seizure-free outcome was seen in (a) 82.8% of pat ients with regionalized EEG seizure without contralateral propagation, but in only 45.5% of patients with contralateral propagation (p = 0.007); (b) 8 4.6% of patients with 100% IED lateralized to one temporal lobe, but in onl y 52.2% with <100% unitemporal IED (p = 0.015); (c) 88.9% with 100% unitemp oral IED and regionalized ictal EEG combined, 73.7% with one of both variab les, and only 33.3% with <100% ipsitemporal IED combined with contralateral ictal EEG propagation (p = 0.007). Conclusions: Switch of lateralization or bitemporal asynchrony in the ictal scalp EEG and bitemporal IED are most probably an index of bitemporal epil eptogenicity in MTS and are associated with a worse outcome.