To characterize laser evoked potentials (LEP), pain psychophysics and local tissue response in fibromyalgia patients.
LEP were recorded in 14 women with fibromyalgia in response to bilateral stimulation of tender and control points in upper limbs by 4 blocks of 20 stimuli at each point. Subsequently, heat pain thresholds were measured and supra-threshold magnitude estimations of heat pain stimuli were obtained on a visual analogue scale. Finally, the extent of the local tissue response induced by the previous stimuli was evaluated.
Laser stimuli elicited two long latency waves: A late wave (mean latency 368.9+/-66.9 ms) in most patients (13/14) from stimuli at all points, and an ultra-late wave (mean latency 917.3+/-91.8 ms) in 78.5% of the patients at the control points and in 71.4% at the tender points. Amplitude of ultra-late waves was higher at the tender points (20.67+/-11.1 microV) than at the control points (10.47+/-4.1 microV) (P=0.016). Pain thresholds were lower in the tender (41.2+/-2.7 degrees C) than the control points (43.9+/-3.2 degrees C) (P=0.008). Local tissue response was significantly more intense at tender than control points (P=0.004).
Ultra-late laser evoked potentials can be recorded simultaneously with late potentials. Our findings are compatible with presence of peripheral C-fiber sensitization, mostly at tender points, probably combined with generalized central sensitization of pain pathways in fibromyalgia.