Over the years, many have viewed Fibromyalgia syndrome (FMS) as a so-called "functional disorder" and patients have experienced a concomitant lack of interest and legitimacy from the medical profession. The symptoms have not been explained by peripheral mechanisms alone nor by specific central nervous system mechanisms. In this study, we objectively evaluated the cerebral response to individually calibrated pain provocations of a pain-free body region (thumbnail). The study comprised 16 female FMS patients and 16 individually age-matched controls. Brain activity was measured using functional magnetic resonance imaging (fMRI) during individually calibrated painful pressures representing 50 mm on a visual analogue scale (VAS) ranging from 0 to 100 mm. Patients exhibited higher sensitivity to pain provocation than controls as they required less pressure to evoke equal pain magnitudes (U(A)=48, p<.002). Despite lower pressures applied in patients at VAS 50 mm, the fMRI-analysis revealed no difference in activity in brain regions relating to attention and affect or regions with sensory projections from the stimulated body area. However, in the primary link in the descending pain regulating system (the rostral anterior cingulate cortex) the patients failed to respond to pain provocation. The attenuated response to pain in this brain region is the first demonstration of a specific brain region where the impairment of pain inhibition in FMS patients is expressed. These results validate previous reports of dysfunctional endogenous pain inhibition in FMS and advance the understanding of the central pathophysiologic mechanisms, providing a new direction for the development of successful treatments in FMS.

BackgroundThere is evidence for augmented processing of pain and impaired endogenous pain inhibition in Fibromyalgia syndrome (FM). In order to fully understand the mechanisms involved in FM pathology, there is a need for closer investigation of endogenous pain modulation. In the present study, we compared the functional connectivity of the descending pain inhibitory network in age-matched FM patients and healthy controls (HC).We performed functional magnetic resonance imaging (fMRI) in 42 subjects; 14 healthy and 28 age-matched FM patients (2 patients per HC), during randomly presented, subjectively calibrated pressure pain stimuli. A seed-based functional connectivity analysis of brain activity was performed. The seed coordinates were based on the findings from our previous study, comparing the fMRI signal during calibrated pressure pain in FM and HC: the rostral anterior cingulate cortex (rACC) and thalamus.ResultsFM patients required significantly less pressure (kPa) to reach calibrated pain at 50 mm on a 0–100 visual analogue scale (p < .001, two-tailed). During fMRI scanning, the rACC displayed significantly higher connectivity to the amygdala, hippocampus, and brainstem in healthy controls, compared to FM patients. There were no regions where FM patients showed higher rACC connectivity. Thalamus showed significantly higher connectivity to the orbitofrontal cortex in healthy controls but no regions showed higher thalamic connectivity in FM patients.ConclusionPatients with FM displayed less connectivity within the brain’s pain inhibitory network during calibrated pressure pain, compared to healthy controls. The present study provides brain-imaging evidence on how brain regions involved in homeostatic control of pain are less connected in FM patients. It is possible that the dysfunction of the descending pain modulatory network plays an important role in maintenance of FM pain and our results may translate into clinical implications by using the functional connectivity of the pain modulatory network as an objective measure of pain dysregulation.

Milnacipran is an effective and safe treatment for pain and other predominant symptoms of FM. Registered as trial no. NCT00436033.

Objective. Mood disturbance is common among patients with fibromyalgia (FM), but the influence of psychological symptoms on pain processing in this disorder is unknown. We undertook the present study to investigate the differential effect of depressive symptoms, anxiety, and catastrophizing on 1) pain symptoms and subjective ratings of general health status and 2) sensitivity to pain and cerebral processing of pressure pain.Methods. Eighty-three women (mean ؎ SD age 43.8 ؎ 8. Results. A correlation analysis including all selfratings showed that depressive symptoms, anxiety, and catastrophizing scores were correlated with one another (P < 0.001), but did not correlate with ratings of clinical pain or with sensitivity to pressure pain. However, the subjective rating of general health was correlated with depressive symptoms and anxiety (P < 0.001). Analyses of imaging results using self-rated psychological measures as covariates showed that brain activity during experimental pain was not modulated by depressive symptoms, anxiety, or catastrophizing.Conclusion. Negative mood in FM patients can lead to a poor perception of one's physical health (and vice versa) but does not influence performance on assessments of clinical and experimental pain. Our data provide evidence that 2 partially segregated mechanisms are involved in the neural processing of experimental pain and negative affect.Pain represents an emotional construct (1,2), and the neural processing of pain can be altered with changes in emotional status (3-6). Mood disorders are This study was performed in collaboration with Pierre Fabre Médicament, Labège, France. The results in this study are derived in part from a placebo-controlled drug intervention study (EudraCT #2004-004249-16) financed by Pierre Fabre Médicament.

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