Abstracts

Rationale: Kurtosis analysis has been applied to magnetoencephalography (MEG) studies in epilepsy patients. The brain regions with high-kurtosis magnetic activities have been shown to correlate with the regions of MEG spike source cluster(s), resection of which was associated with favorable seizure outcome. We determined whether kurtosis analysis of intracranial electroencephalogram (EEG) can estimate the localization of the epileptogenic zone.Methods: We retrospectively analyzed 29 pediatric epilepsy patients who underwent intracranial EEG before focal resective surgery between July 2004 and June 2008. The EEG was recorded using 48-124 (median 110) electrode contacts for 24-216 hours. The EEG signals were sampled at 1 kHz after band-pass filtering at 0.016-300 Hz. We analyzed 10 epochs of 2-minute sleep EEGs that were remote from each other and from seizures by at least 1 hour. We high-pass filtered the EEGs at 20 Hz and calculated kurtosis for each channel. We also detected interictal paroxysms ?20 Hz by amplitude thresholding and calculated their rate, amplitude and duration for each channel. We localized the brain regions with high kurtosis, the seizure onset zone (SOZ) and the regions with high-rate, high-amplitude and long-duration interictal paroxysms ?20 Hz. We tested associations between the surgical resection of those regions and post-surgical seizure outcome, and correlations between kurtosis and the rate/amplitude/duration of interictal paroxysms.Results: There were 14 seizure-free patients (ILAE class 1, 48.3%) and 15 patients (51.7%) who were not seizure free at 1 year after surgery. There were 10 seizure-free patients (ILAE class 1a, 34.5%) and 19 (65.5%) who were not seizure free at 2 years after surgery. Larger resection of the regions with high kurtosis was associated with improved 1-year post-surgical seizure outcome (p = 0.028) but not with 2-year outcome. Kurtosis showed more significant association with 1-year seizure outcome than the SOZ and the rate/amplitude/duration of interictal paroxysms. Kurtosis showed positive, independent correlations with the amplitude and duration of interictal paroxysms (p <0.0001) but not with the rate (p = 0.4).Conclusions: The regions with high kurtosis provide more reliable information to predict post-surgical seizure outcome than the SOZ and the regions with high-rate/amplitude and long-duration interictal paroxysms. Kurtosis reflects combined effects of the amplitude and duration of the interictal paroxysms. High kurtosis suggests the regions with acquired ictogenicity within the irritative zone. These results will also enhance the utility of kurtosis analysis for MEG, which is non-invasive and can cover the entire brain.