Increased pain sensitivity in fibromyalgia: effects of stimulus type and mode of presentation

Fibromyalgia (FM) is defined in part by sensitivity to blunt pressure. Pressure pain sensitivity in FM is evaluated typically by the use of 'ascending' testing methods such as tender point counts or dolorimetry, which can be influenced by response bias of both the subject and examiner. Methods that present stimuli in a random, unpredictable fashion might minimize the influence of these factors. In this study, we compared the results of ascending and random assessments of both pressure and thermal pain sensitivities in 43 FM patients and 28 age- and gender-matched controls. Even though FM is defined on the basis of pressure sensitivity, this group was also more sensitive to heat stimuli, presented in either ascending or random paradigms. In both the patient and control groups, the pain ratings to painful sensations evoked by both thermal and pressure stimuli were significantly greater in the random, compared with the ascending method. The number of subjects classified as 'expectant' because they rated pain higher in ascending than random paradigms was similar for FM and control groups. Both patients and controls exhibited a similar degree of sensitization to pressure and thermal stimuli. The increased sensitivity to both pressure and thermal stimuli for threshold and suprathreshold stimuli in FM patients is consistent with central augmentation of pain processing.