Responsive neurostimulation for epilepsy

Despite the use of anti-epileptic drugs, up to 40 percent of patients with focal epilepsy have drug-resistant seizures. Depending on the location of seizure focus, treatment with surgery might not be appropriate for these patients.

All three campuses at Mayo Clinic offer a new responsive neurostimulation treatment for people with medically intractable focal epilepsy. Results of a clinical trial of the treatment, published in the March 2014 issue of Epilepsia, showed a median 53 percent reduction in seizure occurrence in patients two years after implantation of the device and a 55 percent responder rate.

"This treatment is very innovative because it provides direct intracranial stimulation of the brain," says William Tatum, D.O., a consultant in the Department of Neurology at Mayo Clinic in Jacksonville, Florida. "It's very similar to what cardiologists have been doing for years in terms of defibrillation for the heart."

Although the Food and Drug Administration only recently approved the neurostimulation device, Mayo Clinic has nearly a decade of experience with it through clinical trials beginning in 2005. "It's very exciting to have something other than medications and surgery to offer to patients," says Joseph F. Drazkowski, M.D., a consultant in the Department of Neurology at Mayo Clinic in Phoenix/Scottsdale, Arizona.

Tickling the brain

At Mayo Clinic, surgery remains the preferred treatment when possible for focal epilepsy. However, neurostimulation is an option for patients who aren't surgical candidates due to location of seizure focus. Participants in the clinical trial had focal seizures originating in up to two areas of the brain. The patients averaged three or more disabling seizures a month and had failed to respond to at least two anti-epilepsy drugs.

"The average duration of their epilepsy was over 20 years. These are significantly impacted patients," says Gregory A. Worrell, M.D., Ph.D., a consultant in the Department of Neurology at Mayo Clinic in Rochester, Minnesota.

The neurostimulator is a battery-powered, microprocessor-controlled device, roughly the size of an ice cube, which is implanted in the patient's skull. Leads connected to the neurostimulator are implanted near the patient's seizure focus. The device is designed to detect abnormal electrical activity and to respond by delivering electrical stimulation to normalize brain activity before the patient experiences a seizure.

"Most of my patents are getting many stimulations a day, in some cases over a thousand," Dr. Worrell says. "These patients clearly weren't having a thousand seizures a day. So what the device is actually doing is tickling the brain frequently. That is suppressing the seizures before they really start. Once a seizure starts, we have a much harder time stopping it."

Patients generally require only one day of hospitalization for device implantation. "The recovery is fairly rapid," Dr. Tatum says. "By the next day, patients are walking and talking and ready to go."

Long-term improvement

All three campuses at Mayo Clinic report generally positive outcomes for patients. Unlike anti-epilepsy drugs, whose effectiveness can decline in specific patients over time, the neurostimulator can provide continual improvement. "We have a couple of patients who have failed many different treatments who are now seizure-free," Dr. Tatum says.

Dr. Drazkowski cites the case of a young man who was having difficulty in college because reading triggered his seizures. After determining that surgery wasn't suitable, Dr. Drazkowski offered the option of the neurostimulator. The patient, who has had the device for eight years, no longer has major motor seizures.

"Rarely, he has seizures if he accidentally skips his medication. When he's very stressed, he may have an aura," Dr. Drazkowski says. "But he is now able to attend university." The generator's battery has a life span ranging about a year if several thousand stimulations are required daily to up to four years if hundreds of daily stimulations are needed. Replacing the battery is a 30-minute procedure that involves opening only the skin, not the skull.

"We always ask patients if they want the battery replaced — if the device has improved their lives to that extent — and so far, everyone has," Dr. Drazkowski says.

Potential for new insights

Because the neurostimulator records brain activity, the device potentially will yield data about pre-seizure brain activity. To date, that knowledge has been gained primarily through evaluations of patients in epilepsy monitoring units.

"But now, we'll be continuously obtaining this information for long periods of time from people in an outpatient setting," Dr. Tatum says. "We're basically doing chronic ambulatory direct recording from the brain. There is infinitely greater potential to learn more about predicting seizures."

For more information

Heck CN, et al. Two-year seizure reduction in adults with medically intractable partial onset epilepsy treated with responsive neurostimulation: Final results of the RNS system pivotal trial. Epilepsia. 2014;55:432.