Individual Patient Characteristics Should Guide Choice of Device for Epilepsy Seizure Control

Dr. Heck cited a recent trial of DBS that included 110 patients with epilepsy who had experienced at least six seizures per month and failed at least three antiepileptic drugs. During long-term follow-up, the responder rate was 43% at one year and 68% at five years. Sixteen percent of the patients were seizure-free for at least six months, and scores on the Liverpool Seizure Severity Scale improved over baseline. There was an adverse event rate of 34%.

Noninvasive Stimulation

Another open-loop device is the external trigeminal nerve stimulator (eTNS), which is noninvasive and easy to use, Dr. Heck said. “It’s preset with a certain stimulation algorithm and therefore doesn’t require programming. The patient simply adjusts the current to [his or her] comfort level.”

The eTNS unit includes an electrode that is applied to the forehead. Patients can wear the device at night or under a cap during the day, Dr. Heck said. eTNS is approved for prescription use in the EU, Canada, and Australia as adjunctive therapy for epilepsy in patients ages 9 and older.

In a small, 18-week randomized active control trial of 50 patients with DRE who experienced two or more partial onset seizures per month, researchers observed a 40% improvement in the treatment group versus a 16% improvement in the control group. “Although we don’t have any data on this so far, eTNS may be a convenient way to test whether neuromodulation works for patients before they invest in an implantable device that is considerably more expensive,” Dr. Heck said.

Responsive Neurostimulation

Responsive neurostimulation (RNS) devices are placed under the scalp and within the skull. One or two electrodes connected to the neurostimulator are placed at the seizure focus site.

“At this point, I think that the RNS System [NeuroPace] is the gold standard for responsive closed-loop epilepsy therapy. It responds specifically to cortical activity that represents seizure,” Dr. Heck said. “The cranial implant is not visible, which is good for patients who care about scarring. The small stimulation pulses [are] delivered through the leads directly to the brain and those pulses add up to less than six minutes of electrical stimulation per day on average.” The RNS System received premarket approval by the FDA in late 2013 to treat medically refractory partial epilepsy.

Patients do not know when they are receiving stimulation. RNS “provides an alternative for localization-related DRE when surgery is not an option,” she added. RNS also may be appropriate for patients who have multiple seizure onset zones because more than one electrode can be used to cover various sites.

A disadvantage of using RNS is the shorter battery life, compared with VNS (three to four years vs four to 10 years, respectively). In addition, it is a complex device to use. “I began to work with this device in 2006 and I still would not claim to be an absolute expert yet. I think it’s an exciting kind of technology, but the actual parameters for therapy still need to be worked out,” Dr. Heck said. Because of the need for frequent follow-up visits to program the device, RNS may be a difficult treatment option for patients who must travel long distances.

The RNS System Pivotal trial evaluated responder rates at two years. Patients using RNS demonstrated gradual improvement, with median seizure reductions of approximately 53%, compared with baseline. There were no persistent clinically significant neurologic sequelae.

—Adriene Marshall