Abstracts

Rationale: Medically intractable frontal lobe epilepsy can often be treated with resection of the seizure focus. However in some patients, surgery carries an unacceptable risk for neurological morbidity because of the proximity of eloquent cortex. These patients may be candidates for responsive neurostimulation targeted to the seizure focus.Methods: Patients with partial seizures originating in the frontal lobe were identified from those participating in clinical trials of a responsive neurostimulator (RNS® System, NeuroPace). The seizure onset location and lead location were determined from case report forms. For any patient with valid seizure diary data, the percent change from baseline seizure rate was calculated for the first three month period of each year in the open label period.Results: 39 of the 256 clinical trial patients had seizures that arose solely from the frontal lobe. Of these, 36 were implanted with leads in the frontal lobe and received responsive stimulation there. 34 of these subjects had seizure data at year 1, and 25 had participated in the ongoing trial long enough to provide 6 years of follow-up seizure data. The average age at enrollment was 27.4 years, and the median baseline seizure frequency was 35.8 per month (range 3.7 – 726.7). 50% (n=18) had structural abnormalities on pre-implant MRI, and 13 of these patients had dysplasia. 94% (n=34) had previously undergone video-EEG monitoring with intracranial electrodes. An average of 3.4 leads were implanted per patient; cortical strip leads were implanted in the region of seizure onset in all patients, and 5 patients had depth leads implanted in these regions as well. The median percent reduction in seizures is shown in Figure 1. The likelihood of a favorable response to treatment with the RNS® System was similar in those with MRI identified lesions and those without. There were no serious adverse events related to language, motor or sensory function.Conclusions: Responsive stimulation represents a treatment option for patients with medically intractable lesional and nonlesional frontal lobe seizures who are not candidates for focal cortical resection. Seizure reductions began with the initiation of responsive stimulation and continued to improve over several years, reaching a median of 77% reduction at 6 years. There were no serious adverse events specific to stimulation of the frontal lobe nor were there adverse neuropsychological (Loring et al., 2015) or mood (Meador, 2015) effects.