These investigators also used fMRI to scan study subjects while they received painful pressure stimuli.
“The interesting thing to me is that the nonpainful stimuli were able to classify patients better than the painful stimuli,” says Richard Harris, PhD, associate professor, Chronic Pain and Fatigue Research Center, Anesthesiology, and associate professor, Division of Rheumatology, Internal Medicine, University of Michigan Medical School. “That implies to me that the problem in fibromyalgia is more of a sensory gain problem—like turning up the volume on your radio.” Thus, sensory amplification “may be the more relevant outcome to examine, the more relevant pathological factor driving the symptoms.”
“The complaints that fibromyalgia patients express about being annoyed by nonpainful sensory signals in daily life, such as noises—coming from the TV, for example—or sunlight, or even the contact of bed sheets, fit well with our results, showing strong abnormalities in the processing of these types of stimulus that are not normally painful, but that become unpleasant to patients,” says Marina Lopez-Sola, PhD, first author of the Colorado paper, who is a postdoctoral researcher at that university’s Cognitive and Affective Control laboratory.
All 3 Discomfort Sources Correlate
The Michigan study, which included 42 patients and 20 controls, also subjected patients separately to unpleasant but nonpainful (visual) stimulation, and to pressure pain on the thumbnail bed.2 The patients rated the levels of discomfort using the Gracely Box Scale, a scale ranging from 0 to 20. Patients also rated their current clinical pain. “For fibromyalgia, the pain is spontaneous,” explains Dr. Harris. “They have it all the time at different levels.”
The levels of all three sources of discomfort correlated closely in each patient. From that, “We concluded that visual stimulation is tapping into the neural mechanisms by which fibromyalgia patients experience pain,” says Dr. Harris. “This means that visual stimulation is tapping into some neurobiological structure that’s very intimately associated with the clinical pain the patient experiences, as well as the experimental pain,” he adds, referring to the insula, an area of the brain involved in pain perception.
On top of all that, patients treated with pregabalin who experienced pain relief from the fibromyalgia also showed a reduction in activation of the insula, says Dr. Harris. At the same time, they showed a reduced aversive response to light.
Although not definitive, the evidence from both studies is strong that fibromyalgia is caused within the central nervous system, rather than in the periphery, says Dr. Harris. “When you give people a drug that works to reduce pain and that negates or resolves the altered neurological activity, that suggests the brain is playing more of a causal role. And if that’s the case, that could point the way to potential treatments,” he says.