Abstracts

A novel closed-loop stimulation system referred to as the Responsive Neurostimulation System (RNS) (Neuropace Inc., Moutainview, CA, USA) has been utilized in our institution for the treatment of patients with focal, drug-resistant epilepsy, who are not candidates for surgical resection. In our current communication, we present the surgical technique of implanted RNS, its complications and technical difficulties as well as the preliminary results in our prospective clinical series. The implantable RNS consists of a cranially, extradurally implanted pulse generator, one or two quadripolar strip or depth leads and a programmer. The RNS pulse generator continuously analyzes the patient[apos]s obtained electrocortigrams (ECoGs) and automatically triggers electrical stimulation when specific ECoG characteristics programmed by the clinician as indicative of electrographic seizures or precursor or epileptiform activities are detected. The pulse generator then stores diagnostic information detailing detections and stimulations, including multi-channel stored ECoGs.
The RNS programmer communicates transcutaneously with the implanted pulse generator when initiated by a clinician. The RNS programmer can download diagnostics and stored ECoGs for review. The RNS programmer can be used to analyze stored ECoGs to adjust the detection settings. The RNS programmer can then be used to program detection and stimulation parameters into the implanted pulse generator.
Six patients (2 males and 4 females, mean age 28.6y and age range between 17-42y) have been treated so far in our institution with the above mentioned device. All of these patients underwent phase I and phase II investigation for localization of their epileptogenic foci. Their work-up included surface ictal and interictal EEG, brain MRI, video-EEG monitoring, neuropsychological evaluation and depth and strip electrode implantation for invasive EEG recording and ictal SPECT study. No complications related to the implantable system have occurred in our series. Our follow-up ranges between 4-16 months, mean follow-up time 9.2 months. Five of these patients (83.3%) had more than 45% decrease in their seizure frequency, with one patient (16.6%) demonstrating more than 75% decrease. The other patient (16.6%) had no change in his seizure frequency after implantation. Our preliminary results support the ability of RNS in automatic detection and therapeutic abortion of seizures in patients with well-localized medically refractory epilepsy, not candidates for surgical resection. Further validation of our results is necessary.