Hypersensitivity to cutaneous thermal nociceptive stimuli in myofascial pain and fibromyalgia syndromes

It has previously been shown by this laboratory that patients with irritable bowel syndrome (IBS) exhibit widespread sensitization to thermal cutaneous stimuli. The sensitization was found to extend to segments remote from the symptomatic area, i.e., to the arm and face and was unrelated to the magnitude of spontaneous (visceral) pain. In the present study pain sensitivity was mapped in two additional groups of patients with chronic pain conditions: (a) patients with masticatory myofascial pain (MPS); (b) patients with fibromyalgia syndrome (FMS). The MPS group was carefully screened for confounding comorbidities: e.g., individuals that met the diagnostic criteria for IBS, FMS or arthrogenic pain were excluded as subjects. Pain was induced with a Peltier-device-based contact thermode on the cheek, volar forearm and lateral calf. The subjects rated the thermally evoked pain intensity on an electronic visual analog scale (eVAS). In the first experiment stimulus duration was 3 sec and the interval between stimuli (ISI) 30 sec. The stimulus temperature increased from one stimulus to the next by 0.7 deg until the evoked pain intensity reached 45%. At that point a descending temperature series began which ended when the stimulus was no longer painful. Both patient groups, when compared with a healthy control group, exhibited sensitization at all three stimulation sites. Sensitization was more pronounced in the FMS than in the MPS group. Interestingly, in both groups sensitization was not limited to the spinal segments where spontaneous pain was reported but was equally pronounced in segmentally distant areas. In summary the results suggest that patients with generalized (FMS) or regional (MPS) pain conditions exhibit widespread thermal cutaneous hyperalgesia and a more pronounced dependence on stimulus timing.