Hyperalgesia or hypervigilance? An evoked potential approach to the study of fibromyalgia syndrome

Past research on the phenomenon of enhanced pain sensitivity in fibromyalgia syndrome (FS) revealed evidence for both a higher pain magnitude in response to nociceptive stimuli (hyperalgesia) and a general perceptual amplification of sensations (hypervigilance). In order to distinguish between these two aspects of disturbed sensory processing in FS, cerebral evoked potentials after brief painful laser and auditory stimuli were measured in 10 FS patients. Results were compared with those from age-matched painfree controls. Amplitudes of middle-latency (N1) and long-latency (P2) laser evoked potentials (LEPs) were significantly higher in FS than in controls. Furthermore, laser intensity at pain but not at sensation threshold was lower in FS than in controls. However, auditory evoked potentials (AEPs) did not differ between groups. Enhanced N1 and P2 amplitudes of LEPs suggest stronger sensory and attentional processing of nociceptive information in FS, respectively. The concept of hypervigilance is challenged by the failure to find differences in auditory perception among FS and control patients. Yet, the importance of unpleasant intensities of auditory stimulation, not applied in this study, to reveal abnormal non-nociceptive perceptual amplification in FS is discussed.