Insights Into the Therapeutic Effect of Responsive Neurostimulation Assessed With Scalp EEG Recording: A Case Report

Abstract

The responsive neurostimulation system (RNS) is the first closed-loop neurostimulator approved as an adjunctive treatment for adults with medically refractory focal epilepsy from no more than two seizure foci. In addition to its therapeutic effect, it provides chronic intracranial EEG recordings, with limited storage capacity. Long-term monitoring with scalp EEG recordings can provide additional information regarding seizure patterns, the efficacy of RNS stimulation in aborting individual seizures, and the net effect of RNS on seizure control. We present a 34-year-old woman with medically intractable right temporoparietal lobe epilepsy who failed two resective epilepsy surgeries and MR-guided laser interstitial thermal therapy (MRgLITT), after which RNS was implanted. Long-term scalp EEG performed 16 months after implantation showed continuous right hemisphere slowing and right temporal sharp waves. In addition, RNS stimulation produced bursts of high-voltage, broad-field, surface-negative activity, which allowed correlation of RNS stimulation with scalp EEG patterns. Twenty-seven seizures were captured. Responsive neurostimulation system stimulation did not abort any of the seizures recorded on the scalp EEG. However, the frequency of seizures doubled after RNS stimulation was discontinued and returned to baseline once it was turned back on. This observation supports the neuromodulation effect of RNS.

Analysis of Electrocorticography in Epileptic Patients With Responsive Neurostimulation Undergoing Scalp Electroencephalography Monitoring

“…Another case report was notable for 95% of long events (defined as >30 seconds) correlating with ictal patterns on scalp EEG. 12 This is in line with findings from a recent study that showed stereo-EEG events of longer duration (mean 108.6 vs. 49 seconds) were more likely to be seen on scalp EEG. 13 This finding is also consistent with this study where episodes with a longer duration (median 39.73 seconds) had a higher chance to be read on scalp EEG as electrographic seizures.…”

Practical considerations in epilepsy neurostimulation

“…RNS devices may stimulate several thousands of times per day, with the vast majority of stimulations unassociated with a behaviorally evident or EEG‐evident seizure. This might be sufficient to provide a long‐term neuromodulatory effect, 63 and would be consistent with the observed increasing benefit over time.…”

Therapeutische Neurostimulation bei Epilepsien

“…Dies deutet auf eine allmähliche Modulation des epileptischen Netzwerks hin, ähnlich wie bei anderen Neuro stimulationsverfahren. (3) Eine Wirksamkeit auf die Anfallsfrequenz zeigte sich auch bei Patienten mit im EEG sichtbaren Anfallsmus tern, deren Anfälle nicht unterbrochen wurden [87].…”