Brain 'Pacemaker' Tickles Your Happy Nerve
Marty Graham 05.23.07 | 2:00 AM
The vagus nerve stimulator power pack is implanted near the collarbone, and wired to the left side nerve -- always the left, since the right side goes directly to the heart.
Illustration: Cyberonics Inc.
SAN DIEGO -- A novel medical technique that smuggles an electrical charge into the brain through the vagus nerve is proving at least as effective as medication in controlling severe depression, psychiatrists say.
In vagus nerve stimulation, or VNS, a two-inch diameter, .25 inch thick disk is surgically tucked under the skin near the left collarbone, then wired upward to the vagus nerve in the neck. The battery-operated disk delivers intermittent, rhythmic pulses to the nerve -- whose name means "wandering" in Latin -- that reaches a half dozen areas of the brain critical to treating depression, according to Dr. Darin Dougherty of Massachusetts General Hospital.
"Instead of prescribing milligrams I'm prescribing milliamps," Dougherty says. The implanted disc is programmed and reprogrammed with a wand held over the skin. Data on each patient about the intensity and frequency of the pulse and device settings is stored in individual memory cards slotted into in a handheld computer linked to the wand.
VNS has been used for 10 years to treat epilepsy, where it can cut the number of seizures for some patients by about 40 percent. Doctors began to suspect it held potential for treating severe depression when patients clung to the device, even when it wasn't helping their epilepsy.
"We asked (epilepsy) patients who weren't being helped if we could remove the device and by and large, the patients said, 'No, no, don't take this away,'" says Dr. Mitchel Kling of the National Institutes for Health. "In some cases where there wasn't good seizure control, patients' mood problems stabilized."
The technique won FDA approval as a depression treatment in July 2005. Since then, about 3,000 depression patients have been wired, according to Cyberonics, the Houston-based manufacturer of the device. Doctors gathered at the American Psychiatric Association conference here say they've seen measurable results.
In an October 2005 study, about a third of the severely depressed patients responded well, and almost half went into remission. Ninety-one percent maintained their recovery nine months later, and some patients who didn't report immediate benefits showed improvement and even remission later on.
Researchers know the treatment stimulates norepinephrine and serotonin centers, now treated with pharma at a tepid success rate, and increases blood flow and neuron activity. But they candidly say they don't fully understand why VNS works.
Once healed from surgery, patients report their voices get gravelly during the pulse cycle, usually five of every 30 seconds. If that becomes a problem -- during public speaking, for example -- the device is designed with an off-switch: The patient can suspend the unit by placing a magnet over it, Dougherty says.
Batteries last eight to 12 years, Dougherty says, and drawbacks include a requirement that the patient avoid physical therapy ultrasounds that can heat up the wiring and damage the nerve -- though diagnostic ultrasound works fine -- and problems getting a full body MRI.
The implant neatly sidesteps one of the biggest problem of treating depression: the documented tendency for patients to abandon treatment over side effects or because they feel better.
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