Abstracts

Rationale: Extra-temporal lobe epilepsy has been frequently seen in children with drug-resistant epilepsy. A subset of children with required multilobar resections for epileptic spasms and partial seizures. We have often experienced that seizures demonstrated multiple epileptic foci but skipping the primary motor cortex on the intracranial video EEG (IvEEG). We performed subtotal hemispherectomy sparing motor function to control seizures. By analyzing the degree of stability of phase-amplitude coupling between high frequency oscillation (HFO) and slow wave, we may identify the features of HFO between the seizure onset zone and the primary motor cortex. We hypothesize that pathological HFO are 1) distributed over the multilobar epileptogenic zones in the children with subtotal hemispherectomy, and 2) not found over the the primary motor cortex. Methods: We retrospectively reviewed health records of 23 children with drug-resistant multilobar onset epilepsy, who underwent IvEEG at the Hospital for Sick Children between June 2009 and December 2013. We selected 5 epochs of 5 minutes interictal IvEEG during slow wave sleep. We measured the occurrence rate of HFO at each electrode. We analyzed the distinction between HFO in the seizure onset zone and the primary motor cortex by using the Modulation Index (MI). MI indicated that the strength of coupling between amplitude of HFO and phase of slow waves. Results: The age of 23 children ranged from 1 to 17 years old (mean 9.7 years). The seizure type consisted of epileptic spasms in 10 children and partial seizures in 20 children. 7 children had both seizure types. 14 children underwent subtotal hemispherectomy consisting of fron-temporo-parietal resection skipping Rolandic cortex. Nine children underwent multilobar resections including occipito-temporo-parietal (4), fronto-temporal (2), temporo-parietal (2) and temporo-occipital (1). Postoperative hemiparesis was temporally seen in 3. 18 (78%) out of 23 children became seizure free after the surgery. The mean occurrence rate of HFO at seizure onset zone and the primary motor cortex are 20.4 2.1/min and 4.2 1.1/min, respectively. The seizure onset zone showed significantly larger occurrence rate of HFO than that of the primary motor cortex (p < 0.001). In the seizure onset zone, the mean MI of HFO coupling with slow waves of 0.5-1 Hz, 1-2 Hz, 2-3 Hz and 3-4Hz were 7.1, 8.6, 8.7 and 10.3, respectively. Among the 4 groups of MI of HFO coupling slow waves in the seizure onset zone, MI with 3-4 Hz was significantly higher than that with 0.5-1 Hz (p < 0.001) and that with 1-2 Hz (p=0.034). In the primary motor cortex, the mean MI of HFO coupling with slow waves of 0.5-1 Hz, 1-2 Hz, 2-3 Hz and 3-4Hz were 2.7, 2.7, 2.7 and 2.2, respectively. Among the 4 groups of MI of HFO coupling slow waves in the primary motor cortex, there was no significant difference. Conclusions: In a subset of children with drug-resistant epilepsy, multilobar epileptogenic zones can exist to provoke seizures, especially epileptic spasms. The HFO were significantly located in the multilobar epileptic foci skipping motor cortex. Further analysis of pathological HFO using MI to evaluate slow wave coupling confirmed no epileptogenic HFO over the motor cortex in the children with multilobar onset seizures. Funding: No