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Nerve Stimulation Treatment Approved for Severe Depression
A new therapy for the severely depressed has just received government approval. The FDA's approval of Cyberonics Inc.'s vagus nerve stimulator (VNS) clears it as a potential treatment for those who do not respond to other forms of treatment, approximately 4 million Americans. A clinical trial for VNS's efficacy in treating depression was conducted in 2001, the results of which ultimately convinced FDA administrators. Despite its approval, controversy continues to stir over VNS as the thoroughness and scientific validity of VNS's history of testing is still under question.
The VNS Therapy System is an implantable current generator similar in design to a cardiac pacemaker. It delivers preprogrammed mild electrical pulses to the part of the vagus nerve found in a patient's neck 24 hours a day. The Cyberonics VNS Therapy System was first approved by the FDA in July 1997 for use for reducing the frequency of seizures in adults and adolescents. The generator itself is the size of a pocket watch and is implanted into the chest. Wires snake up the neck to the vagus nerve, delivering tiny electric shocks. The vagus nerve is one of the twelve cranial nerves and is the only nerve that starts in the brainstem and extends all the way down to the abdomen. Needless to say, the vagus nerve is very important. It supplies motor and sensory parasympathetic connections to parts all over the body. The nerve is involved in a variety of tasks, including as heart rate, sweating, and speech. It is thought that through this nerve the limbic system (the neural area associated with emotion) can be stimulated.
In the summer of 2001, Cyberonics began a 200-patient study to test VNS's effectiveness in treating severe depression. An FDA review of the findings of this study ruled that there was no difference in behavior or mood after three months of implant treatment. In response, Cyberonics's researchers argued that a year later, a significant number of the VNS recipients had had their depression ease. However, the yearlong follow-up was not conducted according to standard scientific procedures. For instance, it wasn't a randomized controlled study, just a checkup. As a result, critics questioned its validity. Cyberonics continued to track the VNS recipients, and found that two years later one third of patients in the original study had experienced some response and between 17 percent and 20 percent experienced remission. It was this last bit of data that convinced the FDA. Still, critics have complained that without a comparison group, it's unclear if the implant really helped or the depression eased for some other reason.
There are also risks that need to be considered when being treated with VNS. The chief risk is that more than half of patients in the depression study experienced at least temporary voice alterations (e.g. raspiness) that seem to persist in a significant number, he said. Other complications include difficulty breathing or swallowing.
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