The Role of DNIC in FMS Pain and Treatment
Principal Investigator: Serge Marchand, Ph.D.
University of Quebec, Canada
$49,407 - May 2000
Even if the origin of FMS is unclear, certain biochemical disturbances like serotonin and norepinephrine are well known. Now, these abnormalities may be easily evaluated in a test being used by University of Quebec neuroscientist Serge Marchand, Ph.D., and Pierre Arsenault, M.D., Ph.D., a researcher and practicing physician. This two-man team presented preliminary data at the October American Pain Society meeting indicating that the DNIC or diffuse noxious inhibitory control system is not working properly in FMS patients.
What is the DNIC supposed to do? When noxious or potentially painful signals enter the spinal cord in route to the brain, it is supposed to put a damper on them. The system relies heavily on serotonin and norepinephrine, which have been shown in studies to be low in FMS. Marchand and Arsenault have taken a small group of FMS patients and healthy controls to test the effectiveness of the DNIC in minimizing the pain produced by gradually submersing an arm into an uncomfortably hot or cold water bath. They begin by first submersing the fingertips, then they segmentally work up the arm in eight steps until the whole arm undergoes the painful submersion process.
The DNIC system in healthy people kicked in after just a small portion of the arm was submersed so that these people did not feel much difference between a hand submersed and a whole arm submersed. In the FMS patient group, the DNIC system didn’t appear to work. The more surface area exposed to the painful temperatures of the bath, the more pain the person with FMS experienced.
In the AFSA-funded study, the goal of the investigators is twofold: First, to see if the lack of DNIC system function in FMS patients can be used as a measure to distinguish them from healthy controls, those with depression and those with low back pain, a regional pain syndrome. And, second, to use Effexor-XR (the extended-released version) to determine whether this drug will improve the action of the DNIC system in FMS patients as well as improve their overall functional well-being.
At the American Pain Society (APS) meeting in April 2001, Serge Marchand, Ph.D., explained that there are at least three pain control systems in the body. One is the ascending system that works to minimize the influence of the inputs or signals from the tissues that are traveling to the spinal cord. Another system involves the network of pain processing centers in the brain. The third is the diffuse noxious inhibitory control (DNIC) system. It works mostly in the spinal cord to filter out signals traveling to the brain.
Referring to all three systems, Marchand says the first two seem to be working somewhat in FMS patients, but not perfectly. On the other hand, he says, "The DNIC system doesn't seem to be working at all." Marchand offered three explanations: "a reduction of serotonin, noradrenaline, and maybe an effect of hormones."
Marchand went through his elaborate studies comparing the DNIC function in FMS patients to that of healthy controls. In controls, the DNIC system kicks into action as soon as the pain becomes too intense. In FMS patients, the DNIC doesn't even appear to "turn on" when the painful stimulation gets to be too much. "FMS patients do not have a break from the pain," says Marchand. After a while, the processing centers in the brain become dysfunctional as well.
"What is the future direction for researching the DNIC problem?" asks Marchand. "It's looking at the role of serotonin and noradrenaline drugs on pain perception." With funding from AFSA, Marchand is testing to see if Effexor-ER can restore the functioning of the DNIC system in FMS. Effexor is a drug that increases the CNS levels of both serotonin and noradrenaline. Only half of the study participants had been entered into the trial a the time of his speech. Perhaps at next year's APS meeting, Marchand and his co-investigator, Pierre Arsenault, M.D., Ph.D., will be able to present their final results.