... using fibromyalgia to understand why
(Fibromyalgia Network) - Nearly 100,000 veterans of the first Gulf War have chronic musculoskeletal pain that significantly impairs their function. It's been more than 15 years since these dedicated veterans with Gulf War Illness (GWI) returned from the war and their symptoms persist without a valid explanation.
Dane B. Cook, Ph.D., at the University of Wisconsin in Madison, says that only a "dearth of experimental research directed at pain" has been conducted in GWI, but he suggests that "insight can be gained from research on civilians with fibromyalgia." Cook says that there are some differences between the Gulf veterans with chronic pain and people with fibromyalgia. Most predominately, GWI tends to occur in men exposed to the chemically harsh environment of war while those with fibromyalgia are mostly women whose symptom onset is highly variable but not war-related. What causes or triggers the onset of these two conditions may differ, but what sustains the pain in GWI and fibromyalgia may be very similar processes, according to a series of experiments by Cook.1
Brief and vigorous exercise in healthy young individuals is known to lead to reduced pain sensitivity, often referred to as the "runner's high". However, the opposite occurred in people with fibromyalgia who were asked to ride 30 minutes on a stationary bicycle.2 Cook proposed that veterans with GWI who also had widespread pain similar to fibromyalgia would rate a 30-minute bout of submaximal bicycling exercise as more intense, more painful, and would be more sensitive to pain stimuli when compared to healthy veterans who also served in the first Persian Gulf war. Both groups were physically fit when they were deployed, but upon their return, the GWI group had many unexplained symptoms, including widespread pain.
The recruitment of male research participants who served in the first Persian Gulf war was based on whether they had widespread pain that could not be explained by another illness (such as rheumatoid arthritis). Veterans with regional pain and injuries were also excluded from the study along with rheumatoid arthritis and similar diseases. Eleven participants were classified as having GWI with unexplained widespread pain and 16 met the criteria for the healthy controls.
"Despite exercising at a lower power output, Gulf veterans with chronic musculoskeletal pain still became more sensitive to experimental pain stimuli postexercise," states Cook and colleagues. Leg muscle-pain intensity ratings increased throughout the exercise bout in both groups, but the GWI group with chronic widespread pain reported higher pain ratings that ramped up at a faster rate than the healthy group.
"A significant number of military personnel are no longer able to perform their duties due to multiple symptoms including pain, fatigue, and cognitive troubles," writes Cook. He emphasizes that pain is just one of three factors describing GWI, but considering the lack of experimental data on this condition, Cook adds, "we modeled the design of the present study on similar research conducted in fibromyalgia." The reasons for this are rather straightforward. Psychophysical testing of experimental pain in fibromyalgia has provided strong evidence of abnormal pain processing and now establishes a foundation for future studies that are likely to produce more evidence of abnormal functioning in GWI.
Based on findings in fibromyalgia, the present study suggests a failure of the pain regulatory system in the spinal cord. This would be expected to lead to increases in naturally occurring muscle pain during exercise and exaggerated central nervous system sensitivity following exercise. Repetitive stimulation of the painful sensory receptors in the peripheral muscles during physical exertion is likely the mechanism by which the chronic musculoskeletal pain is maintained in GWI. This is a similar phenomenon observed in a predominantly female population of fibromyalgia patients.
"Exercise research in chronic muscle-pain patients has brought an interesting paradox to light," writes Cook. "Acute exercise appears to exacerbate pain while chronic exercise can reduce pain and improve other symptoms associated with chronic pain."
Last year at the American Pain Society meeting, Cook demonstrated that mild bicycling at an easy level of resistance produced improvements in pain for people with fibromyalgia. More recently, Kevin Fontaine, M.D., of Johns Hopkins University, showed that a prescription for 30 minutes of "lifestyle physical activity," or LPA, up to five days per week significantly reduced pain and improved overall function compared to a group of fibromyalgia patients who attended a series of educational sessions. Daytime fatigue scores and mood remained unchanged for both groups.3
The subjects in the LPA group were instructed to incorporate five to seven bouts of additional daily activities, such as walking, taking the stairs instead of the elevator, housework, gardening, or anything else that gets them moving for a few minutes. The level or intensity of the activity should increase breathing demands but not so much that a person cannot hold a conversation. Initially, the patients began at 15 minutes per day of LPA and worked to 30 minutes by the fifth week (i.e., increasing 5 minutes per week). All subjects wore a waist-mounted pedometer to record the number of steps they took each day and to determine if patients were following instructions.
Before the study, fibromyalgia patients averaged 3,800 steps per day. At the end of the 12-week study, the LPA group increased to an average of 5,800 steps per day, representing a 54 percent increase. Unlike most treatment interventions involving exercise, the dropout rate for the LPA group was small (13 percent) and it was the same as the education group used as a comparison.
"One thing seems clear from the fibromyalgia literature," writes Fontaine, "people with fibromyalgia have difficulty adhering to exercise. Indeed, in fibromyalgia clinical exercise trials dropout rates often nearly exceed 30 percent, suggesting that developing exercise interventions that can be sustained is perhaps as important a goal as finding the particular interventions that produce optimal benefits."
- Cook DB, et al. J Pain March 23 [Epub ahead of print] 2010.
- Vierck CJ, et al. J Pain 2:334-344, 2001.
- Fontaine KR, et al. March 30 Arthritis Care Ther 12(2):R55 [Epub ahead of print] 2010
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