Abstracts

Rationale: Idiopathic generalized epilepsy (IGE) is characterized by seizure activity with diffuse onsets and no proven discrete ictal focus. Over 20% of IGE patients are resistant to anti-seizure medications (ASMs) (Jehi, 2014). NeuroPace’s Responsive Neurostimulation (RNS) System is approved to treat refractory focal epilepsy and is associated with a 75% median seizure reduction rate in long-term follow-up (Nair et al., 2020). Current literature suggests that IGE may originate from the thalamus and its related networks even though epileptiform activity appears diffuse on scalp electroencephalography (EEG) (Paz and Huguenard, 2018). With this in mind, the NeuroPace RNS System was implanted as a palliative intervention in the anterior nuclei of the thalamus (ANT) of 3 patients with drug-resistant IGE. Results of the intervention are reported below.

Methods: A retrospective chart review and intracranial EEG (iEEG) analysis were performed using EPIC and NeuroPace’s Patient Data Management System. Subjects included 3 adult women with severely drug-resistant IGE who had received the ANT-RNS System palliatively at Froedtert Hospital. Subject data was collected from January 2015 through August 2021. Metrics analyzed included epilepsy-related hospitalizations pre- and post-implantation, change in total epileptiform activity, and change in clinical seizures pre- and post-RNS stimulation parameter optimization. Bandpass detection was tuned to 2-4 Hz. Stimulation was programmed for 5 second bursts of 125 Hz delivered to the thalamic channels. Initially set to 0.5 µC/cm2, the charge density was gradually increased at subsequent appointments until a clinical response was obtained (range 1.0 to 3.0 µC/cm2). Simultaneous ASM and RNS device setting changes were avoided.

Results: Two patients were robust clinical responders to the ANT-RNS System (Table). Patient 1 reported improved quality of life. Patient 2 has had no clinical seizures in 9 months and is currently being weaned from ASMs. Patient 3 had an active, chronic infection at the RNS surgical site due to wound picking. This correlates with her increase in overall seizure activity. Her device was removed 18 months after implantation. The infection has resolved.

Conclusions: Thalamic RNS implantation appears to be a feasible method of reducing seizures in IGE. Our results support proceeding to a prospective study investigating the efficacy and potential risks of thalamic RNS in IGE. Formal neuropsychological testing should also be performed to more comprehensively evaluate post-implantation outcomes.

Funding: Please list any funding that was received in support of this abstract.: Medical College of Wisconsin, Department of Neurology - Medical Student Summer Research Program (MSSRP) Fellowship.