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(Abst. 2.051), 2018

Lateralizing, Then Treating Lateralized MTLE With the RNS System: Three Cases and Outcomes Report
Authors: Peter B. Weber, Pacific Medical Center; Emily Mirro, NeuroPace, Inc.; Chad Hamilton, NeuroPace, Inc.; and David King-Stephens, Pacific Medical Center
Content: Rationale: Inpatient video-EEG monitoring provides extensive spatial sampling but is limited generally to 1 to 2 weeks. This may not be sufficient to determine whether patients with mesial temporal lobe epilepsy have unilateral or bilateral onsets. Based on reports that suspected bilateral mesial temporal lobe epilepsy (SBMTLE) can prove to be unilateral after long-term ambulatory monitoring with the RNS System (King-Stephens, et al. Epilepsia, 2015; The RNS® System is an adjunctive therapy for adults with medically intractable partial onset seizures originating from 1 or 2 epileptogenic foci), we have changed our practice so that patients with SBMTLE on the basis of non-invasive localization evaluations move next to treatment and monitoring with the RNS System, rather than undergoing inpatient monitoring with intracranial bilateral mesial temporal coverage.We describe three patients with SBMTLE according to inpatient diagnostic evaluations who were shown to have unilateral onsets with long-term ambulatory monitoring with the RNS System. Methods: All patients were treated with the RNS System using longitudinal bilateral hippocampal depth leads. Bilateral subtemporal cortical strip leads were also placed. Although not connected, if seizures were later determined to be unilateral, the subtemporal cortical lead could be connected to the neurostimulator. Results: Thirteen patients with SBMTLE who were treated with the RNS System for an average of 7.6 years (range: 3.4 – 10.4 years) had leads implanted in the MTL bilaterally. Three (23%) patients were found to have unilateral seizure onsets after review of long-term (1.8 – 3.1 years) ambulatory ECoG recordings. The patients underwent a minor outpatient procedure to change the leads connected to the neurostimulator so that the patient was treated with a hippocampal depth and subtemporal cortical strip lead on the side of seizure onset. Two of these patients are now seizure free. If stimulation benefits had not been substantial and resection was not contraindicated for these patients, then resection of the active MTL would have been a feasible option for these patients. Conclusions: Data from patients with SBMTLE treated with the RNS System in controlled clinical trials suggests that the presumed seizure lateralization based on standard localization evaluations is incorrect in 20% of patients (King-Stephens, et al. Epilepsia, 2015). Long-term ambulatory monitoring with the RNS System allows recording of events over long timescales and helps to determine seizure laterality (King-Stephens, et al. Epilepsia, 2015). The approach described here allows the RNS System treatment of SBMTLE to be easily adjusted if a patient is determined to have unilateral MTL seizure onsets. In this small cohort, treatment of the active MTL resulted in substantial benefit. Funding: None
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