Abstracts

Rationale: Intracranial electroencephalography (iEEG) monitoring is used to guide epilepsy surgery by delineating the epileptogenic zone, however resection may be precluded due to the extent of the epileptogenic zone or the proximity of surgical margins to eloquent cortex. Brain-responsive neurostimulation (RNS) is increasingly utilized in the United States to record and modulate activity from epileptogenic regions that are not surgically amenable. It is unclear whether iEEG monitoring provides a similar benefit to seizure outcomes among RNS patients, especially those with lesional epilepsy in the dominant hemisphere or near eloquent cortex less likely to undergo resection. In this study, we describe seizure outcomes among adult RNS patients according to whether they underwent iEEG monitoring stratified by lesional status.

Methods: We retrospectively identified all adult patients with an active RNS implant, available NeuroPace nSight outcomes report, and ≥6 months of follow-up at our comprehensive epilepsy center. We distinguished patients who underwent iEEG monitoring with subdural or depth electrodes from those who did not undergo iEEG evaluation. Imaging was defined as lesional (or non-lesional) based on the presence (or absence) of abnormalities on MR/PET fusion based on expert neuroradiologist review, regardless of concordance with scalp EEG findings. RNS implants were classified as either mesial temporal, neocortical, mesial+ (one mesial temporal contact and one neocortical contact), or thalamic+ (at least one contact in thalamus). Seizure outcomes assessed at the last follow-up relative to pre-implant seizure frequency were used to categorize patients as either responders (≥50% reduction) or super-responders (≥90% reduction).

Results: Our cohort comprised 82 adult RNS patients (48% female, mean age at implant 33.3 [SD 12.9] years) with an average follow-up duration of 4.1 (SD 2.4) years (range 0.5-9.2 years). Prior treatments included vagus nerve stimulation in 17 patients (21%) and resection in 20 patients (24%); none were previously treated with deep brain stimulation. Based on MR/PET fusion, 71 cases (87%) were classified as lesional. iEEG monitoring was performed in 63 patients (77%). RNS implants were classified as either mesial temporal (n=32, 39%), neocortical (n=33, 40%), mesial+ (n=7, 9%), or thalamic+ (n=10, 12%). At last follow-up, 53 patients (65%) were responders and 29 patients (35%) were super-responders. Among lesional patients, iEEG and non-iEEG groups displayed similar responder (61% vs 79%, p=0.35) and super-responder (30% vs 57%, p=0.07) rates. Among non-lesional patients, responder status was more likely in the iEEG group (100%) than the non-iEEG group (20%, p=0.02), but differences in super-responder status between the iEEG (67%) and non-iEEG (0%) groups did not reach statistical significance (p=0.06).

Conclusions: In our single-center cohort, iEEG was associated with improved seizure outcomes among non-lesional, but not lesional, RNS patients. Given the regional neuromodulation effects of RNS, it may be reasonable for patients with concordant non-invasive diagnostics who are ineligible for resection to skip iEEG monitoring.

Funding: None