Vagus Nerve Stimulation: Is it Good Treatment for Depression

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Vagus Nerve Stimulation: Is it Good Treatment for Depression

The vagus nerve is a long nerve that does many things. It communicates with the brain about sensations in your gut. It conveys information about taste and speech from your mouth. And it affects the actions of smooth muscles that control the circulatory system, your breathing and your digestion. The word vagus comes from Latin, which means "wandering," and wander it does, passing from the brain stem through the neck and chest to the abdomen.

For more than a decade, scientists have reported that electrical stimulation of the vagus nerve can reduce the rate of seizures in epilepsy. In 1997, the FDA approved this treatment, now known as vagus nerve stimulation (VNS), for forms of epilepsy that get no better with drug treatment. In the summer of 2005, the FDA also approved VNS for treatment-resistant depression (TRD), a long-lasting depression that has not improved even after four adequate trials of antidepressants.

Why Is this a Treatment for Depression?

Researchers started trying VNS for depression when they noticed that some patients being treated for epilepsy showed an improvement in mood, no matter how well the treatment worked for their seizures. In a way, this was not so surprising because anti-seizure medications have been helpful to some depression sufferers. VNS also appears to change the function of the nerve circuits and brain regions that are involved in depression.

Does It Work?

The early studies of VNS for depression were open trials in patients with treatment-resistant depression. About one-third to one-half reported some benefit, and almost 30% were described as having completely recovered. For 90% of patients, whatever degree of improvement they achieved persisted. In contrast, more than half of patients treated with electroconvulsive therapy (ECT) relapse within a year.

In open trials, researchers are aware of the therapies that patients receive; treatments are not selected randomly, so valid comparisons of therapies cannot be made. Open trials are easily subject to bias, usually unintentional. So we need to temper our enthusiasm for benefits that appear quite impressive.

Recently, three related studies were published telling us more about how well VNS works. The first — a randomized, controlled trial of VNS for acute depression — was not so promising. In the study, which included more than 200 patients, VNS demonstrated no clear benefit after 10 weeks of treatment.

In the second study, the same group of researchers reported the results of VNS treatment over a 12-month period. Patients reported significant reduction in depressive symptoms, and they gradually got better during the course of the year. But this study was not controlled. So the researchers then compared these patients to depressed patients in a separate 12-month study — in the comparison group, patients were receiving "treatment as usual" for depression. The comparison found small, but significant differences in favor of the VNS group. But again these results are hard to interpret, because this comparison is also not controlled.

Getting the Treatment — What's Involved?

Since 1997, tens of thousands of patients have had the VNS device implanted. A surgeon must wrap electrodes around the left vagus nerve as it passes through the neck and implant a pulse generator on the left side of the chest. The generator is programmed by passing a wand over the chest wall. A stimulus is applied for 30 seconds every 5 minutes and the generator battery lasts 5 to 10 years.

In addition to the possible complications of surgery (post-operative pain and an infection rate of about 1%) and the cost (about $25,000), patients can have symptoms associated with the stimulation. The most common effects are neck, throat, jaw and dental discomfort, as well as headache, hoarseness, alteration of the voice, cough and difficulty swallowing. These problems can be improved by reducing the intensity of the current. Researchers say that patients find the stimulation more tolerable as time passes.

Is it a Treatment Worth Considering?

VNS does not appear to be a dramatically effective treatment for patients with treatment-resistant depression. But the research to date demonstrates that there is a small group of patients who may benefit.

Anyone considering VNS treatment should be aware of its limitations. VNS has not been proven useful in the acute phase of depression. There are still no randomized, controlled trials available to prove the merit of long-term treatment.

VNS should be used only when a person has not responded to several other types of treatment for depression. The person must fully understand the pros and cons because this form of therapy requires a commitment to have surgery and to use the device for at least one year. It takes that long to assess how useful this therapy has been. If no improvement in symptoms of depression is seen after 12 months of use, it is unlikely that continued use will lead to a better result.

Bottom Line

It is always useful to have a novel treatment available for patients with the toughest forms of depression. But we need more research to determine which patients are most likely to benefit from this relatively untested and costly treatment.

Last updated:	September 05, 2008