Abstracts

Rationale: The origin of epileptic spasms (ES) is either focal, generalized or unknown. If they are focal onset seizures, the surgical disconnection of the epileptogenic zone can control ES. The localization and lateralization of the focal onset ES are challenging. Corpus callosotomy (CC) has been reported either diagnostic to lateralize the epileptogenic hemisphere or therapeutic to cure the intractable ES. This retrospective study investigates fast gamma and slow delta wave phase couplings of interictal discharges on scalp EEG to identify the epileptogenic zones of the ES for the evaluation of epilepsy surgeries in children with intractable ES. Methods: We analyzed pre- and post-operative scalp EEGs in 9 ES children without MRI lesion. They underwent surgeries at Osaka City General Hospital (age at initial surgery; median, 2y3m; ranging from 10m to 9y1m). Scalp EEG was obtained using 10-20 international system with a sampling rate of 200/1000 Hz. We collected 20 epochs of 3 min during non-REM sleep. Modulation index (MI) of phase coupling between gamma (30-70 Hz) and delta (0.5-4Hz) was analyzed for 14 electrodes. We excluded C3 and C4, because of the system reference, and Fz, Cz, Pz. We compared pre- and post-operative MI values of 4 quarters of electrodes (left/right, anterior/posterior quadrants) to investigate the correlations with the seizure outcomes. The significant p value indicates <0.05. Results: Total CC was initially performed in 7 patients. In the 7 patients, 5 patients (CC group) underwent CC alone. The other 2 patients (CC+QD group) underwent further quadrant disconnection (QD). The remaining 2 patients underwent only QD including anterior CC (QD group). In 5 patients of CC group, MI significantly decreased at 7 (87.5 %) of 8 quarters after CC in 2 patients who became seizure free. In the other 3 patients with residual seizures, none of MI decreased at all 12 quarters. In 2 patients of CC+QD group, MI decreased at 3 (37.5 %) of 8 quarters after CC with residual seizures. The additional QD significantly decreased MI at all 8 (100%) quarters. They became seizure free after the additional QD. In 2 patients of QD group, MI significantly decreased at 7 (87.5 %) of 8 quarters. They became seizure free. Conclusions: The significantly decremental MI of interictal gamma and delta waves on scalp EEG after CC+/- QD might correlate with the control of ES. For intractable ES patients without MRI lesion, CC can be a diagnostic procedure to lateralize/localize the epileptogenic zone. The CC+/-QD might be a surgical option for the intractable generalized/focal onset ES. The further investigation of MI can support the therapeutic surgeries for the intractable ES. Funding: No funding