Abstracts

Rationale: Temporal lobectomy is the best treatment option for many patients with medically intractable seizures arising from the mesial temporal lobe. However, while the majority of patients attain seizure freedom, 20-35% do not. Persistent seizures may indicate an incomplete resection and/or seizures emerging from the non-resected hippocampus. A second surgery can improve outcome in some patients but others are not candidates due to the risk of postoperative functional deficits. An alternative treatment option may be responsive stimulation delivered to the remaining seizure focus. Methods: The RNS^® System is an adjunctive therapy for reducing the frequency of frequent and disabling seizures in individuals ≥18 years of age with medically refractory partial onset seizures arising from 1 or 2 seizure foci. A cranially implanted programmable responsive neurostimulator is connected to 2 depth and/or subdural leads placed at the seizure focus. The neurostimulator is programmed to detect specific epileptiform electrocorticographic activity (ECoG) and to provide responsive stimulation. Subjects with MTLE and prior temporal lobe resection treated with the RNS System in controlled clinical trials were identified. Implant procedures, lead placement, and stored ECoGs were reviewed. Clinically reported seizures were analyzed for subjects who had ≥ 3 months of seizure diary data during the open label period. The percent change from baseline seizure rate was calculated for the most recent 3 months (last observation carried forward). Results: Twelve of the 256 subjects participating in the RNS System trials had MTLE with a prior temporal lobe resection. Lead placement approaches were: 1. Both leads in the temporal lobe contralateral to the resection (5 subjects); 2. Both leads in the temporal lobe ipsilateral to the resection (2 subjects); 3. One lead in the contralateral and one lead in the ipsilateral temporal lobe (5 subjects). Lead placement was typically a depth lead placed along the long axis of the hippocampus or remaining mesial structures with or without a subtemporal strip. All 10 subjects with lead(s) contrateral to the resection received stimulation in response to detections on that lead(s). Six of the 7 subjects with a lead(s) ipsilateral to the resection received responsive stimulation in response to detections on the lead(s) placed in the remaining mesial temporal structures. The median percent reduction in the clinical seizure rate for all 12 subjects was 78% with a range of 44-100%. Two of the 12 subjects were seizure-free. Conclusions: There is not sufficient power to provide statistical conclusions about the clinical response of patients with MTLE who have undergone a prior temporal lobe resection to treatment with the RNS System. However, descriptive analyses suggest that the clinical response in these patients is not different than the response in patients with MTLE who have not had a prior temporal lobectomy. Overall, responsive neurostimulation achieved seizure reduction in patients with persistent temporal lobe seizures following a temporal lobectomy.