Functional imaging of pain in patients with primary fibromyalgia.

Objective: To examine the function of the nociceptive system in patients with fibromyalgia (FM) using functional magnetic resonance imaging (fMRI).

Methods: Two groups of women, 9 with FM and 9 pain-free, volunteered to participate. In Experiment 1, we assessed psychophysical responses to painful stimuli and prepared participants for fMRI testing. For Experiment 2, subjects underwent fMRI scanning while receiving painful and nonpainful heat stimuli. Conventional and functional MR images were acquired using a 1.5 T MR scanner. Scanning occurred over 5 conditions. Condition 1 served as a practice session (no stimuli). Conditions 2 and 5 consisted of nonpainful warm stimuli. Conditions 3 and 4 consisted of an absolute thermal pain stimulus (47 degrees C) and a perceptually equivalent pain stimulus delivered in counterbalanced order.

Results: Experiment 1 indicated that subjects with FM were significantly more sensitive to experimental heat pain than controls (p < 0.001). In Experiment 2, fMRI data indicated that the FM group exhibited greater activity than controls over multiple brain regions in response to both nonpainful and painful stimuli (p < 0.01). Specifically, in response to nonpainful warm stimuli, FM subjects had significantly greater activity than controls in prefrontal, supplemental motor, insular, and anterior cingulate cortices (p < 0.01). In response to painful stimuli, FM subjects had greater activity in the contralateral insular cortex (p < 0.01). Data from the practice session indicated brain activity in pain-relevant areas for the FM group but not for controls.

Conclusion: Our results provide further evidence for a physiological explanation for FM pain.