Vagus Nerve Stimulation Effective in Resistant Depression
"The regions affected are regions known to be associated with depression, the dorsolateral prefrontal cortex, the orbitofrontal cortex, and the anterior insular cortex.
"These changes in metabolic activity occur prior to any noticeable clinical effects or improvements. The patient does not appear to be getting less depressed, which suggests that the early part of VNS, the first 1 to 5 months, may actually be bringing about changes, or setting the stage, for later clinical effects which will follow 6 months or more," said Dr. Conway
He added that at 12 months, he and his team of investigators also were seeing increases in regional metabolic activity in brainstem regions associated with depression, most especially a region of the brain associated with dopaminergic brain function, the ventral tegmental area.
The study is published online ahead of print in Brain Stimulation.
Profound and Sustained Improvement
Dr. Conway and his team have implanted VNS devices in some 70 treatment-resistant depression patients.
"Although not everyone responds to VNS, we have seen numerous patients experience very profound and sustained improvements in treatment-resistant depression, and many have been doing well for years," he said.
Dr. Charles Conway
The researchers hypothesized that any treatment that brings about such a profound improvement must have observable brain changes associated with it, and this prompted their neuroimaging study.
In the current study, Dr. Conway and his group followed 13 patients with treatment-resistant depression whose symptoms had not improved despite many months of treatment with as many as 5 different antidepressant medications.
Most of the patients had been depressed for at least 2 years, but some patients had been clinically depressed for more than 20 years.
All patients underwent surgery to have the VNS device inserted. The left vagus nerve runs down the side of the body from the brainstem to the abdomen; once activated, the VNS device delivers a 30-second electronic stimulus to the vagus nerve every 5 minutes.
To establish the nature of the treatment's effects on brain activity, the investigators performed positron emission tomography (PET) brain imaging prior to the initiation of stimulation, and again 3 and 12 months after stimulation had begun.
They then compared these brain scans with each other at different time points.
"We used a form of PET which uses radioactively labeled glucose, fluorodeoxyglucose, or FDG," Dr. Conway explained. "The brain is constantly taking up glucose from the blood stream. If there is a regional decrease in metabolism, typically associated with decreased regional brain activity, this can be detected using FDG-PET, because you see less FDG uptake in a given region."
FDA Approved, But Not Widely Available
Eventually, 9 of the 13 patients experienced improvement in depression with the VNS treatment. However, in most cases, it took several months for improvement to occur.
Among those who responded, the FDG-PET scans showed significant changes in brain metabolism following 3 months of stimulation, and this occurred several months before any improvements in their symptoms of depression were noted.
"We saw very large changes in brain metabolism occurring far in advance of any improvement in mood. It's almost as if there's an adaptive process that occurs. First the brain begins to function differently. Then the patient's mood begins to improve," Dr. Conway said.
Although this study is preliminary and a larger version of this study should be done, these findings suggest that antidepressant responders to VNS undergo changes in brain activity associated with regional metabolic activity changes in regions associated with depression, Dr. Conway said.
"The data also suggest that the eventual VNS-responding state involves activation of brainstem regions associated with dopamine activity," he said.
Despite being FDA-approved for treatment-resistant depression, VNS is not easily available for the general public because insurance carriers will not reimburse for the treatment, Dr. Conway said.
"We believe that this study, like many other recent studies as well as our extensive clinical experience, support our clinical observations that this treatment is effective. Also, this population of treatment-resistant depression patients has very few viable successful treatments, and we believe VNS is both effective and has sustained benefit in a significant subset of patients with TRD, and it should be available to those who need it."
Need for Replication
Commenting on the study for Medscape Medical News, William Bunney, MD, Distinguished Professor and Della Martin Chair of Psychiatry, University of California, Irvine, said that the high response rate in this patient population is "therapeutically interesting and may be due in part to the selection criteria used in this research."
Dr. William Bunney
Dr. Bunney added that the observation that the patients did not relapse during a 12-month period "has important treatment implications in a disorder characterized by recurrent depressive episodes.
Although this is a somewhat invasive therapy, it may be justified by the high success rate, particularly if it is replicated in other studies using similar research designs."
Brain Stimul. Published online ahead of print February 15, 2013. Abstract