Abstracts

Rationale: Corticothalamic neuromodulation targeting the pulvinar nucleus is an emerging clinical approach for focal epilepsy patients who are not resective surgery candidates. Recent reports have indicated that subfields of the pulvinar engage select cortical pathways in epilepsy. Specifically, the lateral pulvinar is most strongly connected to the striate and extrastriate visual areas; the ventral portion of the medial pulvinar connects to the lateral temporal cortex; and the dorsomedial pulvinar is connected to the parietal cortex. Hence, RNS® System leads have been implanted in the pulvinar, in addition to a variety of neocortical locations, dependent on each patient's epilepsy network. In addition, it is unclear if the timing of seizure spread through the pulvinar influences efficacy. This review is intended to report the effectiveness of corticothalamic RNS System therapy in a small number of patients treated with a pulvinar and a neocortical lead. It also examines whether the treatment response is associated with very early seizure activity in the pulvinar lead relative to the neocortical lead, as well as programmed stimulation parameters.

Methods: Patients with focal epilepsy who were implanted with both a pulvinar lead and an ipsilateral neocortical lead were included. All patients were treated according to the FDA approved indication for use. Seizure reduction from the pre-RNS System treatment baseline was assessed based on patient reports during follow-up visits using percent seizure reduction quartiles. Only patients with an outcome report at least six months post-implant were included. Each patient was evaluated to determine whether there was ictal activity in the pulvinar lead leading or soon following detection in the neocortical lead, as illustrated in Figure 1, where red arrows indicate early pulvinar involvement before RNS System detection. Treatment response was categorized by responder rate (≥ 50% reduction) for the most recent reported outcome for each patient. Stimulation parameters immediately prior to the time of outcome were reviewed.

Results: Twenty-three (23) patients met inclusion criteria. The mean follow-up was 2.9 years (median 2.8 years). There was early ictal activity on the pulvinar lead in 16 patients (69.6%). The responder rate was comparable in patients with and without early pulvinar ictal activity. Median seizure reduction did not differ significantly between groups (Wilcoxon rank-sum test, p=0.08). Responders were observed across all neocortical lead locations. Eighty-eight percent (88%) of super responders (defined as having 90% or greater reduction in seizure frequency) had a long burst duration ( >1000ms) of stimulation delivered to the pulvinar lead.

Conclusions: In this small cohort, a reduction in clinically reported seizures was observed in patients with drug-resistant focal epilepsy treated with the RNS System and leads placed in the neocortex and pulvinar. Very early ictal activity in the pulvinar did not predict whether the patient would respond. There were responders for each of the neocortical lead locations.

Funding: Not applicable.