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A Promising Treatment for Intractable Epilepsy
by Greg M. Lipshutz, M.D., Division of Neurology,
and Lowell J. Rosman, M.D., F.A.C.S., D.A.B.P, M.,
Division of Neurological Surgery
Vagus nerve stimulation represents a new and promising treatment option for epilepsy patients with intractable seizures. Approximately 70-80% of patients with epilepsy are able to lead normal lives, with their seizures adequately controlled by anticonvulsant medication that has few or no significant side effects., For others, however, seizures may persist in spite of complex regimens involving multiple antiepileptic drugs, or "AEDs". These combinations of drugs often have debilitating cognitive and sedative side effects.
Treatment Pathways
The release of five new AED regimens since 1993 has been beneficial for many epilepsy patients, but some are still unable to achieve adequate control. Intracranial surgery offers an excellent prospect for improvement, and even "cure" for another 5-10% of patients. A number of tests—including EEG, MRI, PET, and neuropsychological testsãare used to determine if an individual is a surgical candidate. Within this surgical group, temporal lobectomy may provide complete relief of all seizures in 80% of properly selected patients. However, for those who are not candidates for these procedures, or who have failed to respond to them, few other treatment alternatives existed until recently.
Vagus Nerve Stimulator
In 1997, the FDA approved use of the vagus nerve stimulator (VNS)— a major and innovative advancement—as a tool for treating intractable epilepsy. The stimulator is a programmable, implantable device that delivers intermittent electrical stimuli to the vagus nerve, a procedure that delivers significant benefits for many patients.
The effects of vagal stimulation on the EEG and on seizure activity had been noted earlier in animal studies, which led to human studies and, ultimately, to the approval of the stimulator for treatment of human epilepsy. The exact mechanism of action is unknown. It is thought to involve activation of inhibitory pathways from the vagus nerve to the brain stem and beyond.
The stimulator device utilizes a battery-powered generator, similar to a cardiac pacemaker, implanted below the collarbone and connected subcutaneously to a bipolar electrode placed on the left vagus nerve in the neck. The procedure is usually done under general anesthesia, and the patient is generally home on the following day. Small currents (0.25-3.5mAmp) are delivered to the nerve on a preprogrammed schedule. In addition, patients are provided with a portable magnet that may be used to activate the device on demand, often terminating or shortening the seizure.
Outcomes
Results of VNS have been dramatic. Initial studies prior to VNS approval demonstrated that approximately 37% of patients had a greater than 50% reduction in seizure frequency at one year, improving to 43% of patients at two years. More recent data since VNS approval in 1997 show even better results, with about three-quarters of patients showing a greater than 50% drop in seizures. Significantly, many patients also note a fall in the intensity and duration of their seizures.
VNS Side Effects
Side effects of VNS are generally limited to hoarseness, throat discomfort, and cough during stimulation—all of which are mild and rapidly dissipate in most cases. Most significantly, there are no associated sedative effects. In fact, many experience improved mental awareness, increased energy and improved mood, which appear to be independent of either improved seizure control or reduction of sedating AED regimen.
VNS at NENA
The VNS experience of our epilepsy team has been typical of results reported nationally. The majority of our patients have seen significant reductions in the frequency, intensity and duration of seizures. Many feel much more alert. Those who can make use of the magnet to activate the stimulator and terminate seizures have found this option extremely useful. We have seen no serious complications, and the common side effects of hoarseness and throat tightness are mild, transient, and well-tolerated.
The case of one VNS patient is instructive. Preoperatively this patient typically had 8-12 generalized tonic-clonic seizures per week, including four episodes in four months of generalized status epilepticus requiring intubation. Two months after VNS implantation, his seizures had fallen to four to five per week. The seizures he did have were shorter in duration, and he had no episodes of status epilepticus in two months.
Epilepsy patients who do not respond to or do not tolerate AED regimens and who are not candidates for intracranial surgery suffer enormous disabilityãloss of independence, risk of injury, and other complications of seizures. Many have lived under a cloud of sedation and cognitive slowing brought on by medications. Vagus nerve stimulation offers many of these patients a new and promising treatment modality that is vastly improving their quality of life.
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