Comparison of clinical and evoked pain measures in fibromyalgia
Richard E Harris1, Richard H Gracely, Samuel A McLean
1Department of Internal Medicine, Division of Rheumatology, University of Michigan, Ann Arbor, Michigan 48106, USA. reharris@med.umich.edu
Unlabelled:
Evoked pain measures such as tender point count and dolorimetry are often used to determine tenderness in studies of fibromyalgia (FM). However, these measures frequently do not improve in clinical trials and are known to be influenced by factors other than pain such as distress and expectancy. The purpose of this investigation was to determine whether evoked pain paradigms that present pressure stimuli in a random fashion (eg, Multiple Random Staircase [MRS]) would track with clinical pain improvement in patients with FM better than traditional measures. Sixty-five subjects enrolled in a randomized clinical trial of acupuncture were observed longitudinally. Clinical pain was measured on a 101-point numerical rating scale (NRS) and the Short Form McGill Pain Questionnaire (SF-MPQ), whereas evoked pressure sensitivity was assessed via manual tender point count, dolorimetry, and MRS methods. Improvements in clinical pain and evoked pain were assessed irrespective of group assignment. Improvement was seen in clinical pain during the course of the trial as measured by both NRS (P = .032) and SF-MPQ (P = .001). The MRS was the only evoked pain measure to improve correspondingly with treatment (MRS, P = .001; tender point count and dolorimeter, P > .05). MRS change scores were correlated with changes in NRS pain ratings (P = .003); however, this association was not stronger than tender point or dolorimetry correlations with clinical pain improvement (P > .05). Pain sensitivity as assessed by random paradigms was associated with improvements in clinical FM pain. Sophisticated pain testing paradigms might be responsive to change in clinical trials.
Perspective:
Trials in fibromyalgia often use both clinical and experimental methods of pain assessment; however, these two outcomes are often poorly correlated. We explore the relationship between changes in clinical and experimental pain within FM patients. Pressure pain testing that applies stimuli in a random order is associated with improvements in clinical pain, but this association was not stronger than other experimental techniques.
