194 Responsive Neurostimulation Targeting the Centromedian Nucleus of the Thalamus Improves Seizure Control in Idiopathic Generalized Epilepsy and Select Multifocal Disease

INTRODUCTION: Although more than 30% of epilepsy patients are drug resistant, many have not traditionally been considered surgical candidates due to generalized or multifocal disease. However, responsive neurostimulation (RNS) of the centromedian nucleus (CM) of the thalamus appears promising for this patient population. We present outcomes following CM RNS for patients with idiopathic generalized epilepsy (IGE) or multifocal disease, with subgroup analyses of patients’ seizure types and targeting methodology. METHODS: 21 patients with drug resistant epilepsy underwent bilateral CM RNS implantation. Electrodes were localized and volumes of tissue activation (VTAs) were modeled in Lead-DBS. Outcome measures were extracted from electronic medical records. Clinical outcomes over time were compared between patients’ seizure types and RNS recorded long-episodes, and VTA overlap with thalamic nuclei was compared between patients with direct and indirect targeting methodologies. RESULTS: For patients with at least 1-year of follow up, average seizure reduction from pre-operative baseline was 81.3%, with 3 Engel class 1 patients, 5 Engel class 2, 8 Engel class 3, and 0 Engel class 4. Average seizure reduction was greatest for non-lesional multifocal patients. Average time to worthwhile seizure reduction was 217 days, and was shortest for myoclonic IGE patients. Long-episodes were associated with seizure reduction in IGE patients only. Direct targeting led to more anterior and medial electrodes with greater VTA overlap with CM. CONCLUSIONS: CM RNS may provide significant relief for IGE and multifocal epilepsy patients. Subsets of these patient populations may particularly benefit from CM RNS. Direct targeting may facilitate more selective stimulation of the CM. The refinement of stimulation targeting, tuning of RNS system parameters, and deliberate patient selection are ongoing areas of investigation.