Abstracts

Rationale:
We computed infraslow network structure in intracranial EEG (icEEG) recordings collected from medically refractory patients pre- and post-antiepileptic drug (AED) taper and studied its relationship with long-term surgical outcome.
Method:
The study was conducted on 21 unselected adult patients with medically refractory epilepsy who underwent icEEG monitoring. Of these, 14 went on to have subsequent surgery and were followed long-term. For each these 14 patients, we selected hour-long segments before and after AED taper when patients appeared to be resting quietly with eyes open. These segments were at least 6 hours removed from seizure. In order to examine infraslow envelope correlations, we computed the mean magnitude-squared coherence (MSC) below 0.15 Hz of the power time-series in the delta, theta, alpha, beta, and gamma bands for all possible electrode contact pairs. Surgical outcomes were rated as excellent outcome (EO) vs. poor outcome (PO) from at least 5-year follow-up. We then determined how icEEG infraslow envelope MSC pre- and post-AED taper varied between the two outcome groups.
Results:
Of the 14 patients studied, 6 were considered PO, and 8 were considered EO. In pre-AED taper segments, we found that in the alpha and beta bands, infraslow envelope MSC was increased in the PO group as compared to the EO group (p< 0.01, Wilcoxon rank sum). However, in the gamma band, infraslow envelope MSC was increased in the EO group (p< 0.01). In post-AED taper segments, the difference between the EO and PO groups was significant in all bands (p< 0.01). However, infraslow envelope MSC was increased in the PO group in the delta, theta, alpha, and beta bands, and higher in the EO group in gamma. We further examined the difference in mean infraslow MSC pre- and post-taper for each outcome group. Interestingly, in the PO group, there was a decrease in mean MSC post-AED taper in the gamma band, whereas the EO group remained largely the same.
Conclusion:
Our results point to a relationship between infraslow network structure during icEEG monitoring and long-term surgical outcome, most prominently in the gamma band. These relationships between outcome groups appear to be stable pre- and post-AED taper, and are frequency-specific with variability across band. We believe infraslow network structure may prove to have some utility in the prediction of neurosurgical outcome in patients with medically refractory epilepsy.
Funding:
:Louis-Argenta Physician Scientist Scholarship (Wake Forest School of Medicine), C.G. Swebilius Trust, 1R01NS109062-01A1 provided by NIH