Abstracts

Rationale:
Responsive neurostimulation (RNS®) is an adjunctive treatment for medically intractable focal epilepsy and can be used in patients who are not candidates for resective surgery. The NeuroPace RNS® system accommodates two stimulating leads implanted into the epileptic foci in the brain, though the relationship between lead location and seizure reduction is unclear. We hypothesize that unilateral implantation of two depth leads into a single hippocampus may lead to improved outcomes through the delivery of electrical stimulation to a larger area within that hippocampus. In this study, we evaluate the seizure reduction outcomes and safety of responsive neurostimulation using dual unilateral hippocampal depth leads.
Method:
We retrospectively compared reduction in seizure frequency in a series of 26 patients treated for mesial temporal lobe epilepsy with responsive neurostimulation. Patients had bilateral, unilateral or dual unilateral hippocampal depth leads implanted for at least one year and had sufficient clinical histories available to determine seizure frequency pre- and post-implantation. Single unilateral patients had an additional cortical strip or depth lead implanted outside of the hippocampus. This included one patient with a lateral frontal strip, one with an anterior subtemporal strip, and three with depth leads in the anterior nucleus of the thalamus. Seizure reduction was calculated as the percent change from the pre-procedural seizure rate to the last reported rate in follow-up clinic visits. Significant difference between groups was assessed by Kruskal–Wallis ANOVA.
Results:
Of the 26 patients, 11 (42.3%) underwent dual unilateral, 10 (38.5%) single bilateral, and 5 (19.2%) single unilateral hippocampal lead placement. The dual unilateral hippocampal group had a median seizure reduction of 84% (range -33-100%), compared to the single bilateral hippocampal group at 82% (42-100%) and the single unilateral hippocampal group at 67% (-13-100%). The difference in seizure reduction between groups was not statistically significant (p = 0.83). Pre-operative imaging was diagnostic of mesial temporal sclerosis in 7 (26.9%) of the total, 2 (18.2%) of the dual unilateral, 3 (30.0%) of the single bilateral, and 2 (40.0%) of the single unilateral group. One single unilateral patient was implanted at an outside center with insufficient imaging available for determination. There were no surgical complications reported in the dual unilateral or bilateral groups. One single unilateral patient required electrode placement revision due to colpocephaly affecting trajectory. Two patients, one in the single unilateral and one in the dual unilateral group, were implanted at outside hospitals and operative notes were unavailable. However, they had no known complications.
Conclusion:
The use of dual unilateral hippocampal leads was surgically safe and achieved similar seizure reduction compared to the standard unilateral or bilateral depth lead implantations. Confounds include that the bilateral implant group may not be strictly comparable to the unilateral groups, and the presence of the non-hippocampal electrode in the single unilateral group. Comparison of dual to single implantation in unilateral patients must await increased numbers of patients.
Funding:
:N/A