Middle and long latency somatosensory evoked potentials after painful laser stimulation in patients with fibromyalgia syndrome.

Ten female patients with fibromyalgia syndrome (FS) were investigated with laser evoked potentials (LEPs) after hand stimulations and compared with 10 female pain-free and age-matched control patients. FS patients exhibited significantly lower heat pain thresholds than controls (P < 0.05) and had higher amplitudes of LEP components N170 (P < 0.01) and P390 (P < 0.05) in response to intensities of 20 W (beam diameter 5 mm, duration 20 msec, wavelength 10.6 microns). N170 additionally appeared with a broader distribution over bilateral central, vertex and fronto-central leads which contrasted to the control group and studies in healthy subjects where N170 was much more restricted to central and midtemporal positions contralateral to the stimulated hand. Auditory stimuli interspersed between laser impulses that served to announce subjects to rate the perceived pain elicited auditory evoked potentials that were not different between groups indicating no differences of general vigilance level to account for observed LEP effects. P390 amplitude enhancement might indicate greater attention and cognitive processing of nociceptive stimuli in FS subjects. Effects upon N170 rather point to exogenous factors like peripheral and spinal sensitization or reduced cortical or subcortical inhibition of nociception.