Abstracts

Rationale: Temporal lobe epilepsy (TLE) is the most common adult epilepsy and the most common drug-resistant focal epilepsy amenable to surgical resection. Evidence suggests that the benefit of surgery for improving seizure control in TLE is best when patients have a majority of seizures originating from one side. Outcomes are less clear for patients with bilateral temporal lobe epilepsy (BTLE). Estimation of the seizure laterality ratio is an important element of surgical decision-making for patients with BTLE. However, estimates of the seizure laterality ratio from scalp video EEG monitoring during standard EMU admissions may be subject to temporal sampling error. Chronic ambulatory electrocorticography offers a valuable source of long-term data to increase accuracy in estimating the seizure laterality ratio. In order to facilitate timely pre-surgical evaluation, better understanding is needed of the minimum number of seizures necessary in chronic ambulatory electrocorticography to obtain reliable estimates of the seizure laterality ratio. In this work, we estimate the minimum number of seizures required for the hippocampal seizure laterality ratio to stabilize.

Methods: A retrospective review was conducted of patients with BTLE at our institution who underwent implantation with responsive neurostimulation (RNS System) between August 2014 and February 2018. Phase 1 EEG data and RNS recordings from 13 patients with BTLE were analyzed. A pseudoprospective approach was used to estimate the minimum number of seizures required before stability in the seizure laterality ratio was obtained. Correlation analysis was performed for Phase 1 video EEG and RNS recordings.

Results: Seizure laterality ratios from Phase 1 video EEG monitoring had a low correlation with seizure laterality ratios obtained from chronic ambulatory electrocorticography. Patients who had only right hippocampal seizures captured during Phase 1 monitoring had as few as nine and as many as 4909 seizures captured with left hippocampal onset when monitored for more than a year. A median of 49 seizures was required before the seizure laterality ratio attained stability, corresponding to a median of 166 days.

Conclusions: Chronic ambulatory electrocorticography offers a unique diagnostic means for improving the accuracy of seizure laterality ratio estimation during pre-surgical evaluation for patients with BTLE.

Funding: Please list any funding that was received in support of this abstract.: None.