Abstracts

Rationale: Responsive neurostimulation (RNS System or RNS) is a programmable device used to treat intractable focal epilepsy. RNS detects seizure activity and responds with pulses of electrical stimulation to reduce seizure duration and frequency. Perception of stimulation has been reported in a small minority of patients, including: photopsia, dysesthesia, muscle twitching, dizziness, and paresthesias (Geller et al, 2017; Morrell et al, 2011). However, the incidence of these phenomena has not been quantified, and the symptom triggers, characteristics, and electrode configuration and programming have not been well-described. The purpose of this study is to determine the incidence of patient perception of RNS stimulation and to explore risk factors for stimulation perception.

Methods: This is a single-center retrospective cohort study of all patients with RNS implanted prior to 2021 and followed clinically at the Oregon Health and Science University (OHSU) Comprehensive Epilepsy Center (n=48).

Results: Four (8.3%) of the 48 patients reported symptoms related to stimulation, three of which (75%) resolved with programming changes. All symptoms began after RNS stimulation parameter changes, were reproducible, and were modifiable with re-programming (see Table 1 for details). Two patients (C, D) experienced transient symptoms of eyelid myokymia during programming, both of whom had 1-2 depth leads in the mesial temporal region, and one had a temporal-occipital depth lead (C). One patient (B) with bilateral superior temporal gyrus (STG) leads perceived several months of “pauses in speech,” which resolved after reprogramming; detailed electrode contact testing identified which contacts triggered speech distortion and were subsequently inactivated. One patient (A) with a right STG lead and a right insular/nucleus accumbens lead experienced persistent symptoms of reproducible auditory “beeps” time-locked to stimulation, as well as transient photopsia that resolved with re-programming.

Conclusions: A minority of RNS patients can perceive stimulation, and most only experience transient symptoms. Slowing the gradual, stepwise modification of stimulation parameters typically facilitates tolerable delivery of stimulation and symptom resolution. Alternatively, problematic electrode contacts can sometimes be identified through detailed testing and subsequent inactivation. STG leads (both depths and strips) may be more likely than other locations to produce prolonged symptoms; in our cohort, four of 48 subjects had at least 1 STG lead and 50% experienced prolonged symptoms.

References:
Morrell MJ, Skarpaas TL, Jarosiewicz B. Responsive cortical stimulation for the treatment of medically intractable partial epilepsy. Neurology. 2011;77(13):1295-1304. doi:10.1212/WNL.0b013e3182302056

Geller EB, Skarpaas TL, Gross RE, et al. Brain-responsive neurostimulation in patients with medically intractable mesial temporal lobe epilepsy. Epilepsia. 2017;58(6):994-1004. doi:10.1111/epi.13740

Funding: Please list any funding that was received in support of this abstract.: none.