Centromedian thalamic deep brain stimulation for idiopathic generalized epilepsy – case series and target analysis

Introduction There is a lack of treatment options for individuals with drug resistant idiopathic generalized epilepsy (IGE). Small, limited case series suggest that centromedian thalamus deep brain stimulation (CM-DBS) may be an effective treatment option. The optimal CM-DBS target for IGE is underexamined. Here, we present a retrospective analysis of CM-DBS targeting and efficacy for five patients with drug-resistant IGE. Methods This single-center case series study included all patients with drug resistant IGE treated with CM-DBS to date. Seizure outcomes were measured with patient-reported seizure frequency. Baseline frequency was taken from the visit immediately before implantation, and it was compared with the seizure frequency from the most recent visit. Stimulation parameters from last clinic visit were used to determine the volume of tissue activated (VTA) by DBS. Lead proximity to target, and VTA overlap with CM nucleus was performed using an open-source toolbox (Lead-DBS 3.0, SimBio/FieldTrip). Associations between the intersection of the VTA and CM nucleus, and seizure outcomes were measured using Spearman’s rank correlation. Results Five patients were identified and included in the study. Median age was 31 (22-45). Median baseline frequency of convulsive seizure was 1.5 per month (0-3.5). Median follow-up time was 13 months (3-23). Median convulsive seizure frequency reduction was 60% (−200-100%). One patient had only absence seizures, with >99% absence seizure frequency reduction. Four out of five subjects had electrode contacts positioned within the CM nucleus target, all of whom had >50% reduction in primary semiology seizure frequency (3 subjects with convulsive seizures, 1 patient with absence seizures). Spearman’s rho was 0.90 (P=0.025). Volumetric “sweet-spot” mapping revealed best outcomes were correlated with stimulation of the middle ventral CM nucleus. Conclusion Our findings suggest that CM-DBS can be an effective treatment for patients with IGE. The extent of overlap between the VTA by DBS and CM nucleus is correlated with the degree of seizure reduction, highlighting the importance of accurate targeting and volumetric targeting analysis.