Why Painkillers Don't Work on Fibromyalgia
Researchers have discovered why many fibromyalgia patients complain that even strong narcotic pain medications fail to relieve their pain. A study at the University of Michigan Health System found that the mu-opioid receptors (MOR) in people with fibromyalgia had a reduced ability to bind to the drugs targeting them.
The researchers did positron emission tomography (PET) scans of 17 women who had fibromyalgia and 17 women who did not. Results showed that the fibromyalgia patients had reduced MOR availability within regions of the brain that normally process and dampen pain signals -- specifically, the nucleus accumbens, the anterior cingulate and the amygdala.
Opioid medications work by binding to opioid receptors in the brain and spinal cord. When those receptors have a lowered availability, the painkillers may not be able to bind to the receptors as well as they should, which means they cannot alleviate pain as effectively. Among the drugs that would be affected by this reduced binding ability is morphine, codeine, propoxyphene-containing medications such as Darvocet, hydrocodone-containing medications such as Vicodin, and oxycodone-containing medications such as Oxycontin.
The research team also found a possible link with depression. The PET scans showed that the fibromyalgia patients with more depressive symptoms had reductions of MOR binding potential in the amygdala, a region of the brain thought to modulate mood and the emotional dimension of pain.
Reference: The Journal of Neuroscience, Sept. 12, 2007, 27(37):10000-10006.