Altered heat pain thresholds and cerebral event-related potentials following painful CO2 laser stimulation in subjects with fibromyalgia syndrome

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Abstract
A decrease in mechanical pressure pain thresholds, particularly over pre-designated tender points, is one of the defining characteristics of fibromyalgia syndrome (FS); however, changes in thermal pain sensitivity have not been investigated. The present study examined heat pain thresholds and cerebral event-related potentials following CO2 laser stimulation in 10 subjects with FS and 10 age-matched control volunteers. The results indicate that patients with FS exhibit a significant reduction in heat pain threshold when tested on the dorsal surface of the hand. In accordance with previous research, we also found a decrease in mechanical pain threshold over pre-designated tender points and at control sites as well as a significantly larger mechanically induced neurogenic flare response. These measures were highly correlated with thermal pain threshold even though different anatomical sites were stimulated. Hence, it seems likely that FS patients display a multimodal change in pain sensitivity which is generalized rather than anatomically restricted. Patients with FS also displayed a significant increase in the peak-to-peak amplitude of the cerebral potential evoked by CO2 laser stimulation at pain threshold intensity and 1.5 times pain threshold intensity. These findings suggest a greater activation of central nervous system (CNS) pathways following noxious input. Putative explanations for the increased CNS response are discussed, including mechanisms of peripheral nociceptor sensitization, altered CNS function and the role of psychological factors.