Objectives: The aim of the literature review was to investigate the criteria adopted by "experts" to diagnose myofascial trigger point (MTrP) pain syndrome. Experts were defined as being either researchers investigating MTrP pain syndrome or the "authority" the researchers cited as a source of reference for MTrP pain syndrome diagnosis.
Methods: We searched electronic databases to identify relevant empirical research (excluding studies not in English and those relating to dental pathology). Of 607 possibly relevant publications 93 met our inclusion criteria. We recorded (1) the individual criterion and criteria combinations used to diagnose MTrP pain syndrome; (2) the cited "authoritative" publications and (3) the criteria recommended by the authoritative publications as being essential for MTrP pain syndrome diagnosis.
Results: The review identified 19 different diagnostic criteria. The 4 most commonly applied criteria were: "tender spot in a taut band" of skeletal muscle, "patient pain recognition," "predicted pain referral pattern," and "local twitch response." There was no consistent pattern to the choice of specific diagnostic criteria or their combinations. However, one pair of criteria "tender point in a taut band" and "predicted or recognized pain referral" were used by over half the studies. The great majority of studies cited publications by Travell and more recently Simons as a principal authoritative source for MTrP pain syndrome diagnosis, yet most of these studies failed to apply the diagnostic criteria as described by these authorities.
Discussion: We conclude that there is as yet limited consensus on case definition in respect of MTrP pain syndrome. Further research is needed to test the reliability and validity of diagnostic criteria. Until reliable diagnostic criteria have been established, there is a need for greater transparency in research papers on how a case of MTrP pain syndrome is defined, and claims for effective interventions in treating the condition should be viewed with caution.