Enhanced central pain processing of fibromyalgia patients is maintained by muscle afferent input: A randomized, double-blind, placebo-controlled study
Staud R et al. – Study demonstrates that lidocaine injections increased local pain thresholds and decreased remote secondary heat hyperalgesia in fibromyalgia (FM) patients, emphasizing the important role of peripheral impulse input in maintaining central sensitization in this chronic pain syndrome; similar to other persistent pain conditions such as irritable bowel syndrome and complex regional pain syndrome.Methods- Aim was to test 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
- Subjects: 22 female normal controls (NCs) and 28 female FM
- 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
Results- NC as well as FM subjects experienced increases of TrapM pressure pain thresholds from lidocaine injections but not from placebo injections
- Additionally, heat hyperalgesia of FM participants was reduced at areas remote from the injection site by lidocaine but not by placebo
- Neither lidocaine nor saline injections affected clinical FM pain ratings, a result most likely due to the very low dose of lidocaine (50 mg) used in this trial
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