Rationale: Intracranial electroencephalography (iEEG) is often used to identify the epileptogenic zone in a discordant epilepsy surgery evaluation. At Swedish Medical Center Colorado, from 2015-2019, the need for iEEG delayed definitive therapy by 6 months or more. Although many centers now include iEEG as part of every surgical workup, in the RNS System Pivotal Trial, only 46% of patients with mesial temporal lobe epilepsy (MTLE) had iEEG prior to implantation, with no difference in outcomes between patients with or without iEEG monitoring (Geller EB, Epilepsia 2017; 58(6):994-1004). Driven largely by the sense of urgency due to the high risk of SUDEP in this pre-surgical population, we reviewed the effectiveness of responsive neurostimulation (NeuroPace RNS® System) in a cohort that did not undergo iEEG monitoring prior to implantation.
Methods:
We retrospectively reviewed our own cohort of patients whose pre-surgical work-up suggested a very low likelihood of an initial resective/ablative therapeutic recommendation. Coupled with additional factors including our own internal implantation safety and efficacy record, and the value of long-term ambulatory iEEG monitoring to inform future destructive therapies, we proceeded empirically with implantation of the RNS System.
All treatments adhered to FDA-approved indications for use. Seizure outcomes were assessed based on patient-reported seizure frequency during follow-up visits, using percent seizure reduction quartiles relative to the pre-implant baseline. Table 1 summarizes treatment considerations to streamline the evaluation process.
Results: The mean follow-up duration was 26.1 months (range: 3–86). At the most recent follow-up, 8 of the 9 patients were classified as responders (≥ 50% reduction in seizure frequency). All patients experienced a minimum of 25% seizure reduction.
Conclusions: In this small cohort of patients with focal DRE and a concordant presurgical evaluation indicating likely mesial temporal lobe epilepsy, treatment with the RNS System - initiated without iEEG monitoring - was associated with a clinically meaningful reduction in seizure frequency. At last follow-up, 8 of the 9 patients achieved at least a 50% reduction in seizures, and all patients experienced some degree of improvement. These findings suggest that in select patients with concordant workup indicating mesial temporal epilepsy, direct implantation of the RNS System without prior iEEG may be a viable therapeutic strategy, potentially streamlining the treatment pathway while still achieving favorable outcomes.
Funding: Not applicable.