Abnormal sensitization and temporal summation of second pain (wind-up) in patients with fibromyalgia syndrome

Although individuals with fibromyalgia syndrome (FMS) consistently report w ide-spread pain, clear evidence of structural abnormalities or other source s of chronic stimulation of pain afferents in the involved body areas is la cking. Without convincing evidence for peripheral tissue abnormalities in F MS patients, it seems likely that a central pathophysiological process is a t least partly responsible for FMS, as is the case for many chronic pain co nditions. Therefore, the present study sought to obtain psychophysical evid ence for the possibility that input to central nociceptive pathways is abno rmally processed in individuals with long standing FMS. In particular, temp oral summation of pain (wind-up) was assessed, using series of repetitive t hermal stimulation of the glabrous skin of the hands. Although wind-up was evoked both in control and FMS subjects, clear differences were observed. T he perceived magnitude of the sensory response to the first stimulus within a series was greater for FMS subjects compared to controls, as was the amo unt of temporal summation within a series. Within series of stimuli, FMS su bjects reported increases in sensory magnitude to painful levels for inters timulus intervals of 2-5 a, but pain was evoked infrequently at intervals g reater than 2 s for control subjects. Following the last stimulus in a seri es, after-sensations were greater in magnitude, lasted longer and were more frequently painful in FMS subjects. These results have multiple implicatio ns for the general characterization of pain in FMS and for an understanding of the underlying pathophysiological basis. (C) 2001 International Associa tion for the Study of Pain. Published by Elsevier Science B.V. All rights r eserved.