Zapping Seizures Away
An implanted device that detects seizure activity in the brain and shocks it away before it spreads could bring new hope to epilepsy patients. The device is part of a growing trend to treat neurological diseases resistant to traditional medication with small jolts of electricity rather than with drugs. Preliminary studies have shown that the device can stop seizures in some patients, and larger-scale studies are now under way.
A full 30 to 40 percent of epilepsy patients fail to find relief from anticonvulsant medications–a percentage that has not improved as new medications have entered the market over the past decade. Some of those patients can be treated with surgery targeting the part of the brain that triggers seizures. But this is not always effective, and not all patients are eligible: someone whose seizures originate in the part of the brain that generates language, for example, would be ineligible for surgery because it might damage his or her ability to speak.
A new device being developed by Neuropace, based in Mountain View, CA, could help these patients. An electrical stimulator, smaller than a playing card and curved in shape, is inserted into a hollowed-out part of the skull. (The procedure is modeled on that of the cochlear implant.) Two electrodes are then implanted into the troublesome part of the brain that triggers seizures. Surgeons locate this spot, known as the seizure focus, prior to surgery using a combination of brain imaging and electroencephalogram recordings (EEG), which measure brain activity from surface electrodes on the skull.
The electrodes monitor nearby neurons for signs of abnormal electrical activity. When they detect signs of an impending seizure, they emit an electrical pulse, blocking the hyperactive wave from spreading throughout the brain. “The idea is to stop the seizure before it occurs,” says Frank Fischer, chief executive officer at Neuropace.
The device, known as the responsive neurostimulation system is just one of a growing number of electrically based devices in development or already on the market. In 1997, the FDA approved the vagus nerve stimulator for epilepsy, which stimulates a nerve leading to the brain. The medical-device company Medtronic is currently sponsoring a trial of deep brain stimulation for use in epilepsy in which an electrode is implanted into a specific spot in the brain. The device is currently approved to treat Parkinson’s disease.
However, the sensing capability of the Neuropace device makes it different than other systems, says Fischer. Other devices deliver a constant stream of electrical pulses, while responsive neurostimulation system zaps the brain only when necessary. “People with a high level of seizure activity would only get a few minutes of therapy a day,” Fischer says. And unlike with vagus nerve stimulator, which can trigger a hoarse voice when turned on, with responsive neurostimulation system, patients can’t tell when the electrical pulses are delivered.
“I think this concept has a stronger scientific basis than constant medication for a condition that comes and goes,” says Ivan Osorio, a neurologist at the University of Kansas Medical Center, who has developed a similar system. “It may also increase [effectiveness] because it addresses changes at the time they occur.”
It’s not yet clear if the therapy will be successful: an ongoing clinical trial of 180 patients is only about 25 percent complete. But early results are promising. The device appears to be well tolerated and does suppress seizures in some patients. “There’s not a lot of efficacy data out there yet,” says Brian Litt, a neurologist and bioengineer at the University of Pennsylvania, who developed some of the algorithms used in the device. “But I’ve seen some beautiful anecdotal recordings where you can see the seizure starting and the device deploying and stopping the seizure without the patient ever knowing.”
The same factors that make the Neuropace device unique also make it more challenging to administer. The location of a seizure and its electrical characteristics can vary from person to person. And neurologists must find the optimal detection and stimulation settings for every individual, a task that involves a certain amount of trial and error.
Each day, the patient uses a wand to wirelessly download electrical data recorded by the device to a laptop, where it is then uploaded for the patient’s doctor to peruse. The doctor can monitor the effectiveness of the therapy and change parameters as needed. “We don’t yet know what the ideal stimulation parameters are,” says Gregory Bergey, director of the Johns Hopkins Epilepsy Center, who is leading one arm of the ongoing trial.
But the data generated during these studies should help. Scientists can analyze the reams of data to create better prediction and detection algorithms, a process that is already under way. “This device is making big contributions to the field, though that doesn’t mean it will make big clinical contributions in its first run,” says Litt.
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