| Emory Report | August 25, 1997 |
Volume 50, No. 1 |
Five Emory patients are among those who participated in studies that led to this month's approval by the Food and Drug Administration (FDA) of a pacemaker-like device to control tremor, said neurosurgeon Roy Bakay, co-principal investigator of the Emory study site.
On Aug. 4, the FDA granted approval to Medtronics Inc. of Minneapolis, to market its Activa Tremor Control Therapy to treat tremor of upper extremities.
According to assistant professor of neurology and co-principal investigator Jerrold Vitek, treatment options until now have involved medication or destructive surgery. The deep-brain stimulation treatment is for patients who have not responded well to drug treatment. The new device is similar to a cardiac pacemaker in that mild electric pulses are sent to tissue (in this case, brain tissue) from a generator implanted within the chest. The studies showed that electric stimulation of the thalamus region deep within the brain blocks nerve signals that incite tremor.
Bakay implants the electric pulse generator just under the skin near the patient's collarbone, then carefully routes an extension wire leading from the stimulator to the inner brain. The wire lead is attached to the inner skull, and the four electrodes extending from it are placed around the thalamus.
"For the first time in three decades we have a completely new approach to treating tremor," said Bakay. "The availability of an implanted electric stimulator that may be externally controlled to reduce or eliminate tremor will change the lives of hundreds of thousands of Americans affected by the disorder. Symptoms have nearly disappeared in most of the patients we've treated at Emory."
Doctors program the device externally, but patients learn to switch the stimulator between high, low and off settings by passing a magnet over their chest. They can tune the simulator to respond to tremor severity-increasing stimulation during stressful times of intense tremor and decreasing stimulation during sleep, when tremor subsides. Batteries are changed every three to five years in a simple procedure.
Similar technology
used to treat epilepsy
Electrical stimulation of a nerve in the neck can reduce or eliminate seizures
by indirectly changing activity in certain brain regions, according to Emory
researchers who helped clarify how the vagus nerve stimulation (VNS) device
recently approved by the FDA works in patients with epilepsy.
Clinical trials performed in human patients showed significantly improved seizure control, but the means by which VNS affected seizures remained unclear. Epileptologist and associate professor of neurology Thomas Henry and his colleagues at the Epilepsy Center carefully evaluated patients using positron emission tomography (PET) and other means before and after Bakay surgically implanted the devices.
"The PET images showed clearly that applying VNS to the left vagus nerve caused a combination of increases and decreases in blood flow in the right and left sides of the brain's limbic system," said Henry. "Abnormal function of the limbic system is critical in starting and spreading most partial-onset seizures."
Henry reports that among the 11 Emory patients who participated in the trials, most have been able to reduce the frequency of seizures, and some have eliminated them.
Several patients who were disabled by their seizures had marked improvement with VNS and are now able to hold jobs. Improved seizure control is often associated with improved self-esteem and quality of life, Henry said.
The pulse generator of the VNS works similarly to the tremor control device but is located just under the skin in the patient's chest.
"VNS itself represents a new era in epilepsy treatment," said Henry. "It is the first FDA-approved epilepsy treatment that involves electrical stimulation of the nervous system. Previously, standard treatment included only medication or surgery to remove abnormal parts of the brain." This new line of treatment is available to the approximately 25 percent of epilepsy patients-more than 500,000 Americans-who never attain seizure control despite exhaustive medication treatments and who are not candidates for available forms of brain surgery."
-Lorri Preston