Altered thermal pricking pain responses of the skin to single and multiple CO2 laser pulses in patients with fibromyalgia

Objective: The aim of our study was to test the response of the skin to short, painful, thermal stimuli, using carbon dioxide-laser pulses in voluntary healthy normal control [HNC] and fibromyalgia syndrome [FMS] subjects. Methods: The experiments were carried out on 18 consenting FMS patients and on 18 consenting HNC. We studied the skin thermal pricking pain threshold and the minimal interval between successive pricking painful stimuli: a sharp pricking pain not accompanied by either thermal or tingling sensations was elicited. The thermal pricking pain threshold was measured on well-defined areas of the skin of the volar surface of the forearm, using pulses of constant power [2W]. The pulse duration needed to induce pricking pain, multiplied by the ratio between the power and the surface of the radiated area, was considered the thermal pricking pain threshold. The minimal time interval between subsequent stimuli that induced sharp pricking pain, accompanied by no other sensations, was measured using a series of over-threshold stimuli of different frequencies. The procedures were fully automatic and were driven by a computer. Results: Both the thermal pricking pain threshold and the minimal time interval were significantly higher in FMS than in the HNC. These parameters are correlated with the basal skin temperature. The latter measurement inversely correlated with the former in FMS; no correlation was found in the HNC. A direct correlation was found between the pain scores and the thermal pricking pain threshold. Conclusions: These findings most probably suggest the presence of some altered biological and energetic equilibrium in the skin of FMS patients.