Abstracts

Rationale: Electrical stimulation of the anterior nucleus of the thalamus (ANT) has previously been found efficacious for reducing seizure frequency in patients with epilepsy. However, while effective in reducing seizure frequency, Deep Brain Stimulation (DBS) in the ANT is also associated with a significant rate of adverse effects. As a closed loop system, responsive neurostimulation (RNS) can provide crucial monitoring data and effective therapy while potentially avoiding side effects associated with open loop systems. We describe three cases of refractory multifocal epilepsy who were implanted with RNS in cortical epileptogenic zones and ANT in an attempt to palliate debilitating seizures in patients with intractable multifocal localization-related epilepsy. Methods: Retrospective chart review was performed on three patients with refractory epilepsy who underwent RNS implantation involving the ANT under the institution’s compassionate use policy. Results: Three patients were implanted with RNS with at least one depth electrode in the ANT and a cortical strip placed in a region of maximal epileptogenicity. Case 1 was a 29-year-old man with multifocal epilepsy refractory to pharmacotherapy and vagus nerve stimulator (VNS). In 22 months of follow-up since implantation, there has been modest reduction in clinical seizure frequency. Case 2 was a 23-year-old man with multifocal epilepsy refractory to pharmacotherapy, VNS, and numerous surgical resections including temporal lobectomy, frontal and parietal corticectomies, anterior corpus callosotomy. In 21 months of follow-up since implantation, focal sensory seizures have resolved; there have been no secondarily generalized seizures and there has been a significant reduction in subclinical seizures. However, the number of disabling atonic seizures and focal unaware seizures remain essentially unchanged; approximately 50% of these arise from regions that are not sampled by the RNS electrodes. Case 3 was a 25-year-old man with multifocal epilepsy refractory to pharmacologic management. In 24 months since implantation, seizures are unchanged in frequency and severity but have decreased in duration. All patients also had modifications of their anti-seizure regimen, limiting interpretation of efficacy.No adverse effects been noted in any patient since implantation. Many but not all seizures had electrographic correlates in the ANT electrode. Conclusions: These findings support that responsive neurostimulation of the ANT unilaterally is feasible, safe, and well-tolerated. No mood-related adverse effects were noted. RNS electrodes placed in the ANT were able to record electrographic correlates and enable visualization of thalamic coupling for many seizures. Overall, the reduction in seizure frequency was modest. Future studies may help assess if this is an efficacious therapy for patients with intractable multifocal epilepsy. Funding: None.