Altered heat pain thresholds & cerebral event-related potentials following painful CO2 laser stimulation in subjects with fibromyalgia (FM syndrome)

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


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.

Gibson SJ, Littlejohn GO, Gorman MM, Helme RD, Granges G

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