Vagus nerve stimulation

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Vagus nerve stimulation (VNS) is an adjunctive treatment for certain types of intractable epilepsy and clinical depression. VNS uses a stimulator that sends electric impulses to the left vagus nerve in the neck via a lead implanted under the skin.

One VNS implanted device consists of a titanium encased generator about the size of a pocket watch; a lithium battery to fuel the generator, with a battery life of ~6-8 years; a lead system with electrodes; and an anchor tether to secure leads to the vagus nerve. This particular device is made by Cyberonics, Inc. Other "wearable" devices are being tested and developed by other companies that involve transcutaneous stimulation and do not require irreversible surgery, damage to the vagus nerve and its surrounding tissue.

Implantation of the Cyberonics, Inc. VNS device is usually done as an out-patient procedure. The procedure goes as follows: an incision is made in the upper left chest and the generator is implanted into a little “pouch” on the left chest under the clavicle. A second incision is made in the neck, so that the surgeon can access the vagus nerve. The surgeon then wraps the leads around the left branch of the vagus nerve, and connects the electrodes to the generator. Once successfully implanted, the generator sends electric impulses to the vagus nerve at regular intervals.^[1] The left vagus nerve is stimulated rather than the right because the right plays a role in cardiac function such that stimulating it could have negative cardiac effects. ^[2]

The exact method of therapeutic action is unknown, but VNS has been shown to affect blood flow to different parts of the brain, and affect neurotransmitters including Serotonin and Norepinephrine which are implicated in depression. Some patients experience an alteration of voice quality and loudness during the time that the pulse is being delivered to the vagus nerve. Other common side effects include hoarseness, throat pain, cough, Dyspnea and Paresthesia.^[2]

In 1997,the United States Food and Drug Administration (FDA) approved the use of VNS as an adjunctive therapy for partial-onset epilepsy. In 2005, the FDA approved the use of VNS for refractory depression. ^[3]

Although the use of VNS for refractory depression has been endorsed by the American Psychiatric Association, the FDA's approval of VNS for refractory depression remains controversial. According to Dr. A. John Rush, vice chairman for research in the Department of Psychiatry at the University of Texas Southwestern Medical Center at Dallas, results of the VNS pilot study showed that 40 percent of the treated patients displayed at least a 50 percent or greater improvement in their condition, according to the Hamilton Depression Rating Scale. ^[4]^[5] Many other studies concur that VNS is indeed efficacious in treating depression. However, these finding do not take into account improvements over time in patients without the device. In the only randomized controlled trial VNS failed to perform any better when turned on than in otherwise similar implanted patients whose device was not turned on.^[6] To better understand the opinions of the medical professionals relating to this treatment option a compilation has been prepared from the responses to CMS (Medicare) during the write-in period from 08/07/2006 - 09/06/2006 entitled "Letters from the Medical Professionals".

Because the vagus nerve is associated with many different functions and brain regions, research is being done to determine its usefulness in treating other illnesses, including various anxiety disorders, Alzheimer's disease, migraines^[3], and fibromyalgia.[1]

Other brain stimulation techniques used to treat depression include Electroconvulsive therapy(ECT) and Cranial electrotherapy stimulation(CES). Deep brain stimulation is currently under study as a treatment for depression. Transcranial magnetic stimulation(TMS) is under study as a therapy for both depression and epilepsy.^[2] Trigeminal Nerve Stimulation (TNS) is being researched at UCLA as a treatment for epilepsy. ^[7]