Enhanced central pain processing of fibromyalgia patients is maintained by muscle afferent input: a randomized, double-blind, placebo-controlled study.

Abstract

Fibromyalgia (FM) syndrome is characterized by pain and widespread hyperalgesia to mechanical, thermal, and electrical stimuli. Despite convincing evidence for central sensitization of nociceptive pain pathways, the role of peripheral tissue impulse input in the initiation and maintenance of FM is unclear. Therefore this randomized, double-blind, placebo-controlled trial of 22 female normal controls (NCs) and 28 female FM subjects tested the effects of trapezius muscle (TrapM) tender point injections with 1% lidocaine on local pain thresholds as well as on remote heat hyperalgesia at the forearm. Prior to muscle injections shoulder pain was standardized by tonic mechanical muscle stimulation, resulting in local pain ratings of 4.0+/-0.5 VAS units. Tonic muscle stimulation was interrupted for the TrapM injections but was continued afterwards at the same level. NC as well as FM subjects experienced significant increases of TrapM pressure pain thresholds from lidocaine injections but not from placebo injections (p<0.001). Additionally, heat hyperalgesia of FM participants was significantly reduced at areas remote from the injection site (forearm) by lidocaine but not by placebo (p=0.02). Neither lidocaine nor saline injections significantly affected clinical FM pain ratings, a result most likely due to the very low dose of lidocaine (50mg) used in this trial.