Evoked pain measures in fibromyalgia

Fibromyalgia is defined by widespread pain and tenderness at a minimum of 11 of 18 defined tender points. Current evidence indicates that tender points are not unique to fibromyalgia and are simply regions in the body where all people are more tender. Tenderness (i.e. sensitivity to pressure) is widespread in fibromyalgia rather than being confined to tender points, and patients are also more sensitive to heat, cold and electrical stimulation. Using the number of painful tender points as a measure of tenderness is clinically expedient but is theoretically vulnerable to bias and is influenced by subjective distress. Other means of assessing tenderness (e.g. pressure dolorimeter devices, or more elaborate psychophysical methods) demonstrate the same increased pain sensitivity in fibromyalgia that is noted with tender point assessments, but these measures are relatively independent of biasing factors or distress. Fibromyalgia is one of only a few syndromes defined by the presence of both spontaneous (i.e. clinical) and evoked (i.e. experimental) pain. While the issues associated with the evaluation of spontaneous pain are shared with all chronic pain syndromes, the issues associated with the evaluation of evoked pain sensitivity are specific to fibromyalgia and related musculoskeletal disorders. This chapter focuses on the evaluation of altered pain sensitivity in fibromyalgia. It describes current measurement methodology, briefly reviews studies of sensitivity to experimentally evoked painful and non-painful sensations, analyses the factors assessed by different measurement methodologies, and concludes with recommendations for future diagnostic criteria and measurement methods.