Responsive Neurostimulation as a Novel Palliative Option in Epilepsy Surgery

Abstract

Patients with drug-resistant focal onset epilepsy are not always suitable candidates for resective surgery, a definitive intervention to control their seizures. The alternative surgical treatment for these patients in Japan has been vagus nerve stimulation (VNS). Besides VNS, epileptologists in the United States can choose a novel palliative option called responsive neurostimulation (RNS), a closed-loop neuromodulation system approved by the US Food and Drug Administration in 2013. The RNS System continuously monitors neural electroencephalography (EEG) activity at the possible seizure onset zone (SOZ) where electrodes are placed and responds with electrical stimulation when a pre-defined epileptic activity is detected. The controlled clinical trials in the United States have demonstrated long-term utility and safety of the RNS System. Seizure reduction rates have continued to improve over time, reaching 75% over 9 years of treatment. The incidence of implant-site infection, the most frequent device-related adverse event, is similar to those of other neuromodulation devices. The RNS System has shown favorable efficacy for both mesial temporal lobe epilepsy (TLE) and neocortical epilepsy of the eloquent cortex. Another unique advantage of the RNS System is its ability to provide chronic monitoring of ambulatory electrocorticography (ECoG). Valuable information obtained from ECoG monitoring provides a better understanding of the state of epilepsy in each patient and improves clinical management. This article reviews the developmental history, structure, and clinical utility of the RNS System, and discusses its indications as a novel palliative option for drug-resistant epilepsy.

Keywords: closed-loop system; drug-resistant epilepsy; focal onset epilepsy; palliative treatment; responsive neurostimulation.

Fig. 1

(A) The neurostimulator and a strip lead. (B) The tablet for physician use and the wand used to access the neurostimulator.

Fig. 2

(A) Neurostimulator kit. 1) Neurostimulator. 2) Craniectomy template. 3) Ferrule. 4) Wrench. (B) Neurostimulator without the connector cover. 5) Lead strain relief. (C) Neurostimulator with the connector cover. 6) Connector cover.

Fig. 3

(A) Skin incision of case #1. The left fronto-temporal craniectomy and occipital burr hole were opened. (B) The depth lead was fixed by the burr hole cap. (C) A metal template was used for the craniectomy. (D) Two selected leads were connected to the neurostimulator and placed on the anchored ferrule. (E) Access to the neurostimulator using the wand. (F) Intraoperative electroencephalography.

Fig. 4

Post-operative skull X-p of case #1. (A) AP view and (B) Lateral view. Two selected leads were connected to the stimulator (white arrow).

Fig. 5

Preoperative MRI images of case #2: (A) Axial View and (B) coronal view. The images show paraventricular heterotopia. Post-operative skull X-p of case #2: (C) Lateral view and (D) AP view.