The solution to some untreatable cases of epilepsy may take the form of a small, implantable electrical stimulation device, say neurologists at Baylor College of Medicine and St. Luke’s Episcopal Hospital in Houston participating in a national study on adults with the disorder.
The implantable device, called a responsive neurostimulator is designed to detect the onset of seizures and suppress them before any symptoms appear, much like implantable cardiac pacemakers are intended to detect abnormal heart rhythms and then deliver electrical stimulation to correct them.
Electrodes are surgically implanted in epileptic regions of the brain and then connected to a small computerized device, the neurostimulator, which is embedded within the skull. The RNS then continuously monitors a patient’s brainwaves. The device is programmed by a neurologist to detect and electrically disrupt abnormal brain activity that may precede a patient’s seizures. The neurologist is also able to reprogram the device wirelessly using a laptop computer in order to make more precise detections in each individual.
“Electrodes are placed on an individual basis depending on where the seizures are coming from,” said Dr. Eli M. Mizrahi, professor of neurology and pediatrics at BCM, director of the Baylor Comprehensive Epilepsy Center, and chief of neurophysiology at St. Luke's Episcopal Hospital. “The RNS senses the seizure and may stop it or stop its spread.”
The RNS, developed by NeuroPace, Inc., attempts to deliver relief to those epilepsy patients for whom medications or conventional epilepsy surgery are either ineffective or unfeasible. Existing options for patients with epilepsy who are medically untreatable and don’t qualify as good surgical candidates are limited to experimental drug trials, a ketogenic diet (which is high in fat and low in carbohydrates to minimize glucose intake), and vagus nerve stimulation – all of which can lead to “some improvement but typically not a complete elimination of seizures,” according to Mizrahi, principal investigator of the BCM-St. Luke’s Episcopal Hospital site, one of 28 nationwide.
Responsive neurostimulation differs from conventional brain stimulation techniques, which involve scheduled stimulation of specific regions of the brain irrespective of the brain’s activity. While scheduled brain stimulation has proven effective in treating certain movement disorders such as Parkinson’s disease, it has not been successful in cases of epilepsy.
“In contrast to traditional forms of neurostimulation, the RNS device uses computer technology to recognize and respond to specific patterns of brain activity,” said Dr. Daniel Yoshor, assistant professor of neurosurgery at BCM, who is implanting the RNS device for this study. ”It doesn’t just constantly stimulate the brain according to a set schedule.”
Epilepsy affects roughly 2.5 million Americans of all ages. As many as 50 percent of persons with epilepsy continue to have seizures despite the use of anti-epileptic medications. Patients with poorly controlled epilepsy are not allowed to operate vehicles, and many are unable to remain gainfully employed for an extended period of time.
“Many patients with epilepsy continue to have seizures even while on appropriate anti-epileptic medications, so they’re always fearful that they could have a seizure any time,” said co-investigator Dr. Amit Verma, assistant professor of neurology at BCM. “Many of the patients who have epilepsy develop social phobias and can’t do the kinds of daily activities that many people take for granted.”
“There is a tremendous potential here to fill a niche in patients who may not be treatable with medications and may not be good candidates for surgical removal of the epileptic part of the brain,” said co-investigator Dr. Ian L. Goldsmith, assistant professor of neurology at BCM.
The only other study site in Texas is The University of Texas Southwestern Medical Center at Dallas.