Implanted device may help short-circuit epileptic seizures
Epileptic seizures often strike without warning, causing debilitating convulsions and blackouts. Some sufferers don’t go out in public for fear of embarrassment; a few aren’t permitted to drive.
Medications and surgery can control symptoms, but at least 5% of the nation’s 2.5 million epilepsy sufferers get no relief from current treatments. Now researchers have hit upon the idea of controlling the attacks at their source -- the brain.
An implanted nerve stimulator, which works like a pacemaker for the brain, may be able to prevent seizures, enabling thousands of people disabled by epilepsy to lead normal lives.
“This is an exciting approach that could greatly improve the quality of life for people in whom medicine and surgery haven’t worked,” says Dr. Gregory L. Barkley, a neurologist at Henry Ford Hospital in Detroit and a scientific advisor to the Epilepsy Foundation in Landover, Md.
Epilepsy is a baffling neurological disorder in which the brain’s electrical functioning is disturbed. It can be triggered by brain injuries, tumors, high fevers or strokes. The condition also runs in families, but in 70% of cases, the cause is unknown.
Normally, the brain controls body movement and organ function through electrical impulses that are carried throughout the body by the central nervous system. In epilepsy, this regular pattern is occasionally interrupted by brief bursts of intense electrical activity, triggering muscle spasms, nausea, convulsions and loss of consciousness.
The experimental electronic device, called the Responsive Neurostimulator System, is programmed to identify seizures before any symptoms appear and to normalize the haywire activity by delivering a mild jolt to the brain.
Previous research has suggested that electrical stimulation can stop a seizure.
“Seizures consist of a pool of nerve cells firing extra discharges repetitively,” says Dr. Douglas Labar, a neurologist at Weill Cornell Medical College in New York who is testing the device. “Like a cardiac defibrillator, counter shocks cause those nerve cells to fire together, which throws off the abnormal excessive rhythm and allows the whole system to reset.”
Before the device is implanted, patients undergo tests such as MRI scans and EEG monitoring, so that doctors can analyze their seizure pattern and pinpoint the region of the brain where the seizure starts. This approach works best for patients whose seizures start in one spot, says Labar, rather than several places in the brain.
In most cases, patients are hospitalized for one to two weeks while their brain waves are continuously monitored by external electrodes. Doctors use this information to program the device so it will recognize the patient’s seizure pattern. Then the stimulator, which is about the size of a pocket watch, is surgically inserted under the scalp and fastened to the skull.
The device, which contains a tiny computer chip that continuously records brain wave patterns, is connected to the brain by two electrodes that are attached to the region where seizures originate. Then, when the device detects the “signature” of the onset of a seizure, it emits a mild electrical current to block it.
“From previous experience, we think it’s critical that the electrical stimulus is delivered early to abort the seizure,” says Dr. Robert R. Goodman, a neurosurgeon at Columbia University College of Physicians and Surgeons in New York who is also testing the device. “Even a fraction of a second delay may be too late to stop seizure activity, which can spread rapidly.”
Based on the brain wave readings collected by the device’s computer chip, patients get their computer fine-tuned once a month, and they will be monitored for two years. Six patients have had the device implanted; doctors hope to enroll 200 patients at 15 medical centers across the country.
“This device offers the chance that we could cure people without having to disturb brain function,” Goodman says.
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Other implant options
Another implanted electrical stimulator is being tested to prevent epileptic seizures. Called the Intercept Epilepsy Control System, the brain stimulator emits consistent electronic signals to stabilize brain activity.
The device has three components: a battery-powered neurostimulator, which is implanted in the chest; two insulated wires that are threaded from the stimulator to the head; and electrodes that are attached to two areas of the brain. The device, which is being tested on 124 volunteers at 12 sites in the U.S., is for patients whose seizures originate in several areas of the brain.
An older implant for epilepsy, the Vagus Nerve Stimulator, which was approved by the Food and Drug Administration in 1997, also delivers short bursts of electricity every few minutes. However, it targets a large nerve in the neck, the vagus, with the idea that the nerve transmits the stimulus to the brain. That stimulator, used primarily by people who don’t respond to medication and are not candidates for surgery, reduces seizure frequency in nearly half of patients.
