symptoms of fibromyalgia, a poorly understood but potentially
debilitating condition that affects up to 12 million people in the
U.S. (4 percent of the population), a small pilot study has found.
"We have a medication that seems to have low side effects and seems
to reduce pain and fatigue [in fibromyalgia patients]," says Jarred
Younger, a pain researcher at Stanford University School of Medicine
and co-author of the study appearing today in Pain Medicine. "I think
this is a potential treatment to add to the doctor's arsenal," he
adds, noting that longer studies involving more patients are needed
to confirm the results.
Fibromyalgia, a mysterious ailment whose symptoms include chronic
widespread muscle pain, fatigue, sleep problems, anxiety and
depression, often appears between the ages of 34 and 53 and is more
common in women (affecting 5 percent of women and 1.6 percent of men
in the U.S.), the researchers report. The U.S. Food and Drug
Administration (FDA) has approved three drugs for treating
fibromyalgia, but many patients don't respond to them, Younger says.
For 14 weeks, Younger and his colleague Sean Mackey, chief of the
pain management division at Stanford, monitored the symptoms of 10
women ages 22 to 55 with fibromyalgia before, during and after they
took small doses (4.5 milligrams per day) of naltrexone, a drug that
for about three decades has been used to wean addicts off of heroin
and other street drugs. (Naltrexone works by latching onto nerve cell
receptors where heroin and other opioid drugs would dock, thus
blocking their ability to act on the cells and induce a feeling of
being high.) Using handheld computers, the women reported the
severity of their daily symptoms on a scale of one to 100 (100 being
the most severe). Every two weeks, they visited the researchers who
downloaded the data entered in the computers and ran tests to measure
the women's pain thresholds for pressure, heat and cold applied to
the skin.
Their findings: the severity of pain and fatigue fell by 30 percent
during the weeks the women were taking naltrexone compared with those
in which they were taking a placebo. Two of the women said the drug
gave them vivid dreams and one said she had nausea and insomnia the
first few nights that she took the pills, but otherwise no side
effects were reported.
Younger, who suspects fibromyalgia is an autoimmune disorder (in
which the body's immune system attacks healthy tissue), speculates
that naltrexone is alleviating fibromyalgia symptoms not by blocking
nerve cell receptors but by dampening the activity of microglia—
immune cells in the brain and spinal cord that produce pro-
inflammatory cytokines, which excite nerve cells responsible for
creating the sensation of pain.
"These results are promising," says Dan Clauw, an anesthesiologist at
the University of Michigan at Ann Arbor's Chronic Pain & Fatigue
Research Center who was not involved with the study. But Clauw is not
convinced that naltrexone works by suppressing immune cells; he
thinks low doses of the drug might stimulate nerve cells to release
pain-alleviating endorphins.
Regardless of how the drug works, the scientists agree that more
research is needed to confirm these preliminary findings. The
Stanford team is already about two thirds of the way through a 24-
week follow-up study involving 40 patients. And although Younger
hasn't started analyzing the data, he says, "The participants seem
happy…I think it looks good."
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