Abstracts

Rationale: Responsive neurostimulation (RNS) provides significant and sustained seizure reduction in individuals with bilateral mesial temporal lobe (MTL) epilepsy. The differences in treatment response between those with and without evidence for mesial temporal sclerosis (MTS) have not been elucidated. This study aims to stratify seizure outcomes based on presence or absence of MTS on magnetic resonance imaging.

Methods: This was a single-center retrospective study of a consecutive series of patients with evidence for bilateral MTL epilepsy who underwent RNS system implantation between 2008 and 2022. Patients who underwent temporal lobe resection prior to or alongside RNS implantation were excluded. The primary outcome was frequency of disabling seizures at 2-year follow-up. Seizure outcomes data among those with bilateral MTS, unilateral MTS and no MTS were compared.

Results: We identified 30 patients who underwent RNS implant with bilateral MTL leads. A minimum of 2-year follow-up data was available in 26 patients, 17 of whom had intracranial electroencephalography data. Six patients had bilateral MTS, five had unilateral MTS (4 left, 1 right), and 15 did not have imaging evidence for MTS, although 6 of them had other temporal lobe lesions. Only one of the 6 patients (16.7%) with bilateral MTS achieved >50% seizure reduction at 2 years. Two additional patients achieved >50% seizure reduction at the latest follow up. 50% or greater seizure reduction was achieved in 3 of 5 patients (60.0%) with unilateral MTS and in 10 of 15 (66.7%) of patients without MTS at 2-year follow-up. None of the patients with bilateral MTS achieved Engel Class l-II outcomes, whereas 2 patients with unilateral MTS achieved Engel Class II outcomes and 6 patients with no MTS achieved Engel Class I-II outcomes. One of these patients achieved Engel Class IA, and another individual achieved Engel Class ID. Two patients with bilateral MTS subsequently underwent unilateral selective amygdalohippocampectomy, since which Engel Class I was achieved.

Conclusions: Seizure reduction may be less impactful in individuals with bilateral MTS undergoing RNS therapy compared to those with unilateral MTS or no MTS. Additionally, it may take longer to achieve a significant seizure reduction in those with bilateral MTS. This finding is important for counseling patients with bilateral MTS being considered for RNS therapy. Subsequent unilateral resection or ablation may be considered in select candidates with unsatisfactory response to bilateral MTL RNS therapy.


Funding: None