Rationale: Previous studies have shown that localized ictal scalp EEG onset is predictive of the surgical outcome for all types of focal epilepsy. We evaluated the scalp interical and ictal EEG characteristics as they relate to the yield of stereoelectroencephalography (SEEG) localization and surgical outcomes in MRI-negative adult patients with refractory focal epilepsy. Methods: Adult and pediatric MRI-negative patients were identified from a departmental SEEG database from 2016 to 2019. Focal interictal or ictal, scalp or SEEG finding, was defined as involving a single lobar region (or on scalp EEG, contiguous neighboring regions, e.g., frontotemporal), and non-focal as hemispheric (two or more non-contiguous lobar regions), bihemispheric, multifocal, or diffuse. Results: In 26 patients who met the inclusion criteria, gender and hemisphere of seizure onset were evenly distributed, and average age at SEEG implant was 28.6 years, with average follow up of 13.4 months. Extratemporal (n=16, 64%) and bilateral (n=18, 69%) implantations were respectively more common than temporal (n=9, 36%) and unilateral (n=8, 31%) implantations.Focal ictal SEEG onset was seen in 7/11 (63.6%) with focal interictal scalp EEG, 10/15 (66.7%) with nonfocal interictal scalp EEG, 13/15 (86.7%) with focal ictal scalp EEG, and 4/11 (36.4%) with non-focal ictal scalp EEG. No statistical difference emerged between ictal or interictal scalp EEG and focality of SEEG onset, although the majority of patients with focal ictal scalp EEG demonstrated focal ictal onset on SEEG.Of 17 patients who had an identified focal ictal onset on SEEG, resective surgery or ablation was recommended in 11, and eight patients underwent a procedure (two temporal, six extratemporal). Four patients achieved ILAE one outcome, one patient ILAE 2, and three patients ILAE 4 or 5. The four patients with ILAE 1 outcomes included two temporal and two extratemporal patients.Six patients with focal SEEG ictal onset underwent neuromoduation therapy with either RNS or continuous subthreshold cortical stimulation(CSCS). Of the nine patients with non-focal SEEG ictal onset, two had DBS and one had corpus callosotomy. Of the four patients who had ILAE 1 outcome with ablation or surgical resection, three had focal scalp ictal onset and all four had focal SEEG onset. However, interictal data were non-focal in three patients on scalp EEG and three patients on SEEG. Conclusions: Our study suggests that focal scalp ictal EEG onset is associated with focal onset on SEEG and favorable surgical outcome. Neither scalp EEG nor SEEG interictal data were associated with focal onset on SEEG. Funding: Please list any funding that was received in support of this abstract.: None. Click here to view image/table
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