Vagus Nerve Stimulation: Promising Fibromyalgia Treatment Possibility
A pilot study published online this month in the journal Pain Medicine evaluated the safety and effectiveness of vagus nerve stimulation for patients with treatment-resistant fibromyalgia.
The vagus nerve is actually a pair of nerves, also known as the tenth cranial nerve. The term "vagus" is Latin for "wandering" -- an appropriate name for this meandering nerve that takes a long, wandering path through the body from its origin in the medulla oblongata (a part of the brain stem) to its end at the colon. The vagus nerve influences a number of different brain processes and conveys information about various body organs to the central nervous system.
Vagus nerve stiumlation (VNS) involves implanting a small device (similar to a pacemaker) just below the collarbone. A wire from the stimulator is then run to an electrode attached to the vagus nerve. Once the stimulator has been implanted, it is programmed to generate pulses of electricity at set intervals.
VNS is currently approved by the FDA for use with treatment-resistant epilepsy and depression patients. The testing and use of VNS with these patients revealed a surprising but welcome side effect -- pain relief. It is hoped that VNS will change the way pain information is relayed to the brain and thus will be an effective adjunct therapy for fibromyalgia patients who have not responded to other treatments.
Study Design and Results
14 fibromyalgia patients were implanted with a VNS stimulator in this open-label study. Two of them were not able to tolerate stimulation and did not continue with the study. 12 patients completed the initial three-month segment of the study and 11 of them went on to complete the full 11 months.
In order for VNS to be considered effective, patients had to show measurable improvement in pain, overall wellness and physical function. A secondary measurement was the loss of both pain and tenderness criteria for the diagnosis of FM.
At three months, five patients had met the criteria for effectiveness. Two of those five no longer met the widespread pain or tenderness criteria for FM. The therapeutic effect seemed to increase over time in that additional participants had attained both criteria at 11 months. Side effects included stimulus-bound voice alteration, neck pain, nausea, shortness of breath, dry mouth and fatigue.
VNS is certainly an interesting new avenue to pursue in the search for more effective treatment options for FM. We have to keep in mind, though, that this was a very small trial, so we can't jump to conclusions until much larger numbers of FM patients have tried it.
As with most fibromyalgia treatments, it seems to have been most effective for about a third of the people in the study (five out of 14), although apparently a few more had a positive outcome after using the device for 11 months. Given that VNS requires implantation, I would hope that researchers will find a way to screen for those patients who are most likely to have a positive response. It's one thing to try an oral medication for a couple of months knowing there's a 30% chance it will help. It's quite another to undergo a surgical procedure with only a 30-35% chance of success.
Another concern I have is that a Medscape article I read about this study indicated that "there were four unanticipated/serious adverse events occurring in four patients," however, exactly what those adverse events were was not mentioned. Four serious adverse events out of only 14 initial patients seems like a lot to me.
I look forward to seeing what future clinical trials reveal.
Lange G, et al. Safety and Efficacy of Vagus Nerve Stimulation in Fibromyalgia: A Phase I/II Proof of Concept Trial. Pain Med. 2011 Aug 3. [Epub ahead of print]