Middle & long latency somatosensory evoked potentials after painful laser stimulation in patients with fibromyalgia (FM) 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.

Lorenz J, Grasedyck K, Bromm B

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