Abstracts

Rationale: Intracranial electroencephalogram (IEEG) is the gold standard for localizing the ictal onset zone in children with refractory epilepsy undergoing neurosurgery. There is little published data on the inter-rater reliability of ical onset pattern (IOP) classification and timing and duration of pediatric IEEG. We conducted a study to determine inter-rater reliability of IOP classification in pediatric patients undergoing subdural IEEG and analyzed timing of IEEG seizures and associated surgical outcomes. Methods: We performed a retrospective review of pediatric patients with refractory epilepsy who underwent subdural IEEG monitoring followed by epilepsy surgery at our institution from January 2007 to October 2016. Seizures recorded on IEEG were reviewed independently by two blinded epileptologists. Statistical analyses were performed to assess inter-rater reliability and associations between IEEG timing variables and surgical outcomes. Results: Twenty-three patients were identified who met inclusion criteria. Age range at time of IEEG was 4-20 (mean 13.5) years. 784 seizures were recorded (3-244 seizures per patient).IOPs were categorized into two types: those that included low voltage fast activity (LVFA) and those that included rhythmic activity without LVFA. In 16 patients (70%), the predominant IOP type included LVFA. In 7 patients (30%), the predominant IOP type was rhythmic activity without LVFA. Inter-rater reliability was fair (kappa = 0.51). When the epileptologists attempted a more detailed classification scheme with five IOP categories, inter-rater reliability was poor (kappa=0.32).When the area of the IOP was subsequently resected, favorable outcome was accomplished in 14 patients (Engel Class I, 61%). 11/16 patients (69%) in whom the predominant IOP included LVFA had favorable outcomes, compared to 3/7 patients (43%) in whom the predominant IOP did not include LVFA (odds ratio 2.93, 95% confidence interval 0.47-18, p=0.25). 5 patients had only one IOP type recorded; 4/5 of these patients (80%) had Engel Class I outcomes. Compared to patients with worse surgical outcomes, patients with Engel I outcomes spent significantly fewer days on IEEG (mean 5.89 vs. 9.33 days, p=0.0122), had their first electroclinical seizure sooner after IEEG monitoring started (mean 43.4 vs. 89.1 hours, p=0.0509), and had a larger number and a significantly larger percent of seizures captured in the first three days of IEEG recording (52.1% vs. 17.6% of seizures, p=0.0107). Conclusions: This study is significant because it demonstrates that inter-rater reliability when evaluating for the presence of LVFA at ictal onset on IEEG in children is fair, but reliability for more detailed IOP classification is suboptimal, so improved pediatric IOP classification schemes are needed. Larger pediatric studies are needed to determine whether LVFA at ictal onset is predictive of surgical success in children. Regardless of ictal onset pattern, outcomes tended to be good for patients in whom seizures occurred within the first few days of IEEG monitoring, suggesting possible benefit to eliciting seizures rapidly in children undergoing IEEG. Funding: None