From Issue No. 240 of Medical Science Bullitan


 

Generic Name: Vagus nerve stimulator

Trade Name: NeuroCybernetic Prosthesis System

Use: Reduction of seizures in people who remain refractory despite optimaldrug therapy

On January 27, 1997, the U.S. Food and Drug Administration (FDA) received anapplication for marketing of a device that would help reduce seizures inpeople who remain refractory despite the utilization of optimal drugtherapy. This device is called the NeuroCybernetic Prosthesis System and ismanufactured by Cyberonics, a company based in Houston. The process ofapproval was expedited by the favorable recommendation of the NeurologicalDevices Panel of FDA's Medical Devices Advisory Committee. This device wasapproved as an adjunct to drug or surgery in patients with partial-onsetseizures.

How It Works

Vagus nerve stimulation was first tried in 1988 as a treatment for seizures.This idea was proposed by Jacob Zabarra, who believed that stimulation ofthe vagus nerve might disrupt or prevent a seizure. Through animal studies,he was able to show that brain wave patterns can be changed via vagus nervestimulation. This proposed theory serves as the backbone for the modern-dayvagus nerve stimulator (VNS).

The NeuroCybernetic Prosthesis System is a vagus nerve stimulator . Agenerator is implanted under the collarbone, much like a pacemaker. Thisgenerator is then connected to the vagus nerve in the neck. At this site,the generator regularly releases electrical signals 24 hours a day,regardless of seizure activity. These signals are relayed to the brain andare responsible for maintaining control of any seizure activity. This deviceincludes an external programming system, which is used by physicians tocontrol stimulation settings. Patients can also turn this device on or offby placing a magnet directly over it.

The exact mechanism of action of this device is not fully understood.However, there are two hypotheses. The first theory states that theanticonvulsant activity of the VNS is caused by an increased threshold ofthe connections to the nucleus. The second theory states that the continuouselectrical stimulation of the vagus nerve increases the number of inhibitoryneurotransmitters and decreases the number of stimulatory neurotransmitters.

Clinical Tips

In one study, the safety and effectiveness of this device were tested. Themajority of patients showed some improvement while using the VNS. Fiftypercent of those enrolled in this study showed at least a 20% reduction inthe number of seizures per day, and 25% of patients reported a 50% reductionin the frequency of seizures. In contrast, 20% of patients demonstratedincreased seizure activity. Treatment with the vagus nerve stimulator wasnot free of side effects. Patients experienced cough, hoarseness,alterations in their voice, and shortness of breath.

Another study tested the safety and tolerability of this device bymonitoring patients for changes in vital signs and electrocardiographicactivity, and for the occurrence of adverse events. The authors concludedthat the lack of change in both vital signs and electrocardiographicactivity dictates that this device can be safely implanted for use as ananticonvulsant.

Approximately 1.7 million Americans suffer from epilepsy. The vast majorityof these patients can be controlled by conventional drug therapy. However,more than 200,000 people remain refractory to pharmacologic intervention.This device may serve an essential function in their lives.

References

Ben-Menachem E. Modern management of epilepsy. Vagus nerve stimulation.Bailliere's Clin Neurol. 1996;5(4):841-848.

Friedman M, Wernicke JF, Caldarelli DD. Safety and tolerability of theimplantable recurrent laryngeal nerve stimulator. Laryngoscope.1994;104(10):1240-1244.

HHS News: U.S. Department of Health and Human Services, 1997.

1997 VirSci Corporation. All rights reserved.As seen on PharmInfoNet (http://pharminfo.com )


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