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September 25, 2002


Vagus Nerve Stimulation for Epilepsy Treatment – A Five-Year Review Following FDA Approval

Vagus nerve stimulation (VNS), an electrical stimulation therapy currently used to treat epilepsy, can help reduce seizures in patients while increasing activity and alertness in the brain. Since its approval by the Food and Drug Administration (FDA) in July 1997, a number of animal and human studies have been conducted to determine the various uses and outcomes of VNS.

In a review article in the journal Neurology, Thomas Henry, M.D., associate professor of neurology, Emory University School of Medicine and director of the Emory Epilepsy Center, examines the different methods, or mechanisms, of VNS tested and used over the past five years. Because of his expertise in the fields of epilepsy and vagus nerve stimulation, journal editors selected Dr. Henry to write the review article, published in the Sept. 23 issue of the journal.

"The reason for this review paper is to evaluate the therapeutic mechanisms of vagus nerve stimulation, how it works, how to maximize its uses and how not to use it in inappropriate situations," Dr. Henry explains. "Because VNS reduces or stops seizures through multiple mechanisms and actions, this paper may be beneficial to physicians and researchers who are looking for the precise treatment of an individual."

More than two million people in the U.S. have epilepsy, a chronic medical condition produced by temporary changes in the electrical function of the brain, causing seizures that affect awareness, movement, or sensation. Most people don't know why they have epilepsy. There is no known cause of epilepsy, however the greatest known cause is head injury followed by infections, tumors and strokes. Patients who suffer from partial seizures (seizures that affect only one side of the brain), who do not respond well to antiepileptic drugs and who cannot undergo brain surgery are all good candidates for VNS.

Stimulation of the vagus nerve is thought to affect some of its connections to areas in the brain that are prone to seizure activity in people with epilepsy. Surgeons implant a small stimulating device, similar to a cardiac pacemaker, just under the skin in the left chest area. A connecting wire is run under the skin from the device to the vagus nerve in the left side of the neck. Three small leads, or wires, are then carefully attached to the nerve. Pre-programmed, mild, intermittent electrical pulses are then delivered 24 hours a day to the nerve, slowing or stopping seizures. Because the left vagus nerve sends information to both sides of the brain, researchers only need to stimulate that one side. In 1997, the FDA approved use of the VNS for patients, 12 years of age and older, with partial seizures.

"Most of the research in VNS has been done during the past five years, following the FDAs approval," says Dr. Henry. "During that time, weve found VNS can do more than just slow or stop seizures. Past studies show VNS can increase activity of the brain chemical, norepinephrine, which acts as a neurotransmitter in the brain, and can antagonize seizures in epileptics. Boosting norepinephrine can also relieve depression, but more studies are needed to determine if vagus nerve stimulation can be used as a treatment for depression."

Researchers have also found VNS increases activity in the reticular activating system of the brain, a network in the brain that controls arousal and alertness. Patients often report improved alertness during VNS. Several previous studies have also shown evidence of improved learning and memory during stimulation, although behavioral effects of VNS have not been completely studied in animals or humans.

To determine how much the brain is aroused from thinking and learning before, during and after VNS, Emory researchers looked at the amount of cerebral blood flow in the brains of patients with epilepsy. Using position emission tomography (PET) scans, 10 Emory patients were scanned before receiving a treatment of VNS and again within 20 hours after treatment was administered (known as acute VNS). Half received high levels of stimulation, while the other half received low levels of stimulation.

In both groups, blood flow changes showed increased synaptic activity in the so-called "sensory strip" of the brain, the major site for cerebral processing for sensory activity on the left-side of the body. Widespread blood flow increases occurred in areas of reticular, autonomic and limbic systems in both hemispheres, areas important in maintaining alertness, memory and mood, with more areas of blood flow increases at higher levels of stimulation.

Patients were then scanned again, following three months of intermittent VNS (known as chronic VNS). Half received high levels of stimulation and half received low levels of stimulation. While these scans showed an increase in cerebral blood flow, they revealed smaller volumes of significant activations than the previous scans. More studies are needed to determine the difference in findings between acute and chronic stimulation through PET scans, but researchers say PET scans may reflect brain adaption to chronic stimulation of the left vagus nerve.

Like most implantable devices, there are some complications that may been seen following surgery. Patients may experience tingling in the neck, hoarseness and a slight cough during nerve stimulation.

"During the past five years of VNS research, weve determined that various mechanisms of VNS can help in reducing seizures in those with epilepsy, not just one single mechanism," says Dr. Henry. "Through these means and as research progresses in this field, we feel we can help a certain population of patients with epilepsy obtain manageable seizure control and maintain a good quality of life."

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