Responsive neurostimulation: Candidates and considerations.

Responsive neurostimulation (RNS) has recently emerged as a safe and effective treatment for some patients with medically refractory focal epilepsy who are not candidates for surgical resection. Responsive neurostimulation involves an implanted neurostimulator and intracranial leads that detect incipient seizures and respond with electrical counterstimulation. Over 1800 patients have been treated with RNS since its FDA approval in 2013. Despite its widespread use, however, RNS presents distinct challenges for clinicians. What types of patients are most well-suited for treatment with RNS? Given the availability of two other neurostimulation modalities, vagus nerve stimulation (VNS) and thalamic deep brain stimulation (DBS), what patient characteristics favor or disfavor RNS? Once RNS candidates are identified, lead placement presents another challenge. Unlike VNS and thalamic DBS, which both involve prespecified electrode locations, RNS involves intracranial strip and/or depth electrodes that can be flexibly configured based on knowledge of the seizure onset zone. The efficacy of RNS may depend on optimal lead configuration, but there are few resources to guide clinicians in formulating lead placement strategies. Here, we address these challenges, first by reviewing clinical trial data supporting the safety and efficacy of RNS. Then, through a series of clinical vignettes from our center, we provide a framework for RNS patient selection. For each clinical scenario, we illustrate typical strategies for RNS lead placement. We outline considerations for choosing among available neurostimulation devices based on their intrinsic features. For example, a unique feature of RNS is that the neurostimulator provides chronic electrocorticography (ECoG), which has powerful diagnostic potential. We highlight emerging applications of chronic ECoG, and we discuss how the limitations of RNS will inform development of next-generation devices.