Abstracts

Rationale: Given the deep-seated location of the insula as well as its proximity to eloquent cortex and critical cerebrovascular structures, targeted neurostimulation techniques for patients with refractory insular/opercular epilepsy, specifically responsive neurostimulation (RNS), has gained attention as a credible treatment option for well-selected patients [1,2]. Indeed, RNS is efficacious in insular epilepsy, as recent case reports have demonstrated up to a 75% reduction in seizure frequency 12-18 months following RNS implantation into the insula/operculum [3,4]. More widespread use of RNS in insular/opercular epilepsy may be expected, though optimal stimulation parameters for adequate seizure control with avoidance of adverse stimulation effects have yet to be characterized.

Methods: We report a case of a patient with right-sided insular/opercular epilepsy treated with RNS who developed recurrent episodes of yawning, dyspnea, and laryngeal constriction after scheduled increases in RNS charge density, accompanied by increased interictal discharges on ECoG. A 34 y/o RH male with refractory focal epilepsy due to viral encephalitis was previously treated with VNS then a right temporal lobectomy after sEEG with bi-temporal sampling; an associated pre-surgical brain MRI showed right mesial temporal sclerosis. Despite these interventions, the patient continued to have seizures characterized by viscerosensory/autonomic complaints and left limb paresthesias, concerning for a right insular or opercular focus.  He underwent repeat sEEG evaluation which identified independent seizure foci within the right anterior operculum and insula, resulting in RNS implantation to these locations. 

Results: The patient reported a 25-30% reduction in disabling seizures 8 months following RNS implantation. RNS lead charge density was increased to 1.0uC/cm² 8 months following initial lead placement, and then to 1.5uC/cm² 3 months later. While the increase of RNS charge density to 1.0uC/cm² led to an improvement in seizure frequency, the adjustment to 1.5uC/cm² was associated with new episodic yawning, laryngeal constriction, and dyspnea, atypical for his prior seizure semiology. In association, RNS ECoG data demonstrated prolonged runs of interictal discharges in the right opercular contacts at 1.5uC/cm² charge density (Image 1). Both ECoG and clinical episodes improved when RNS charge density was reduced.

Conclusions: As in a prior case series, this case demonstrates the potential limitations to RNS stimulation settings, due to observed increases in interictal activity recorded on ECoG with higher stimulation intensities in insular/opercular contacts [3]. In our case, this observation was also accompanied by new clinical complaints. Given the expected gain in utility of RNS for insular/opercular epilepsy, optimal stimulation parameters and lead placement within these locations should be adequately characterized for patient safety and comfort.
_x000D_ References:_x000D_ 1. Jobst BC, Epilepsy Curr. 2019;19 (1):11-21. _x000D_ 2. Rey-Dios R. Neurosurgeon Focus. 2013;34(2):E6._x000D_ 3. Chen H. Epilepsia Open. 2017;2(3): 345-349. _x000D_ 4. Smith JR. Stereotactic Funct Neurosurg. 2010;88(5):281-287.

Funding: Not applicable