The Role of DNIC in FMS Pain and Treatment
Principal Investigator: Serge
Marchand, Ph.D.
University of Quebec, Canada
Award: $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.
Project Update
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.