Abstracts

Rationale: Hypsarrhythmia is known as abnormal interictal EEG pattern of infantile spasms/West syndrome. However, pathophysiological mechanism of hypsarrhythmia is still unknown. Epileptic fast oscillations were observed before the onset of West syndrome, even after developing hypsarrhythmia and during ictal epileptic spasms. We adopted total corpus callosotomy(CC) in children with infantile spasms and achieved good seizure outcome and developmental improvement.Our aim of this study is; 1) to analyze the characteristic features of fast oscillations and phase synchronization in hypsarrhythmia, and compare with interictal EEG changes and seizure outcome after CC; 2) to identify new markers for predicting seizure outcome after surgery in children with infantile spasms.We hypothesized that the origin of hypsarrhythmia might involve both epileptic cortex and subcortical structures stimulated by cortical discharges. The recruitment of callosal system might play a role to produce the chaotic EEG pattern. Integration of fast oscillations and phase synchronization in hypsarrhythmia would decide the prognosis of infantile spasms after surgical treatment. Methods: We retrospectively identified children with infantile spasms who underwent CC from 2009 to 2014. We collected 20 epochs of 10 seconds pre-operative hypsarrhythmia for each child. The characteristic features of spectral power and phase synchronization in hypsarrhythmia were analyzed, and compared to interictal EEG changes and seizure outcome after CC. Results: We found 42 children with infantile spasms who underwent CC. We could categorize post-operative interictal EEG changes as 3 groups; GroupA: no epileptic discharge(10 children), GroupB: lateralized epileptic discharges(10), and GroupC: bilateral epileptic discharges(22). There was no significant difference among clinical profiles of 3 groups. All 10 children of GroupA achieved seizure freedom after CC. In GroupB, lateralized epileptic discharges after CC led to further resective surgeries. 7 of 8 children who underwent further resective surgeries achieved seizure freedom. The spectral power in hypsarrhythmia was higher for GroupB and C, compared to GroupA. This effect was localized around the central electrodes, and was getting stronger towards higher frequencies. The phase synchronization at theta and higher range were increased in GroupC and distributed widely across the electrodes. Those at 1-2Hz range was increased in GroupA and had a tendency to be around the central electrodes. Conclusions: Extent of epileptic cortex with fast oscillations might relate with malignant  epileptogenicity in hypsarrhythmia against CC. Recruitment of callosal system might play a role to generate the chaotic EEG pattern. Latent fast oscillations and phase synchronization in hypsarrhythmia can predict seizure outcome in children with infantile spasm. Funding: No