Myofascial trigger points (MTPs) are routinely diagnosed and treated by clinicians in many musculoskeletal health disciplines. MTPs have been associated with numerous clinical conditions and prevalence studies claim that they may account for 30-85% of patients complaining of regional muscular pain.1 Despite the widespread acceptance of MTPs as an important clinical entity the diagnosis of MTPs is a source of continuing controversy. There are no accepted biochemical, electromyographic or diagnostic imaging criteria recognised as a definitive diagnostic gold standard.2 Furthermore, there is currently no reliable list of physical diagnostic criteria for MTPs.1 The detection of MTPs is solely dependent on manual palpation and patient feedback. These circumstances have raised concerns regarding the non-substantive manner in which MTPs are identified.
In the absence of an accepted gold standard, physical diagnostic tests should demonstrate inter-rater reliability in order to be considered clinically useful. Myburgh et al.3 have recently published the first systematic review of reliability studies examining evidence for the use of manual palpation for identifying MTPs. The reviewers used a comprehensive search strategy across relevant medical databases and the reference lists of related articles. The search revealed eleven relevant studies, however five studies were subsequently excluded because they did not use appropriate statistical measures of agreement. The remaining six studies were then assessed for internal validity and reproducibility according to predetermined quality criteria.
The included studies examined the use of manual diagnosis for MTPs in a variety of settings, populations, conditions and clinicians. This heterogeneity limited pooled analysis of the results. In addition, none of the studies used completely overlapping diagnostic criteria, and no single muscle was observed in more than two studies. The results of the quality analysis indicated two studies to be of high quality, one of moderate quality, and three of low quality. None of the MTP criteria were found to have a high level of evidence. At best, the current literature suggests moderate evidence for the reliability of local tenderness in the trapezius, and pain referral at gluteus medius and quadratus lumborum; however a single reliable criteria is insufficient to diagnose a MTP according to commonly cited diagnostic criteria. The authors concluded that the current evidence supporting the reliability of diagnostic palpation for MTPs is weak and further high quality studies are required.
The clinical uncertainties surrounding MTP diagnosis present challenges to the interpretation of all research on MTPs. In the absence of an accurate diagnosis, the results of any epidemiological, pathophysiologic or clinical investigation will be misleading.1 A potent example of this is seen in the subsequent issue of the same journal, where Ettlin et al.4 report on the prevalence of cervical MTPs in four different clinical populations and a group of healthy controls. Having assumed that identification of each of the MTP characteristics is reliable, the researchers state that a clinically relevant MTP was present if three out four listed criteria were met. However, using this methodology it is possible that the diagnostic process would identify presentations other than MTPs, such as non-specific muscle pain, pain of peripheral nerve trunk origin, underlying joint sensitivity, secondary hyperalgesia, or even normal intramuscular physiology. It also explains their report of active MTPs in up to one third of the pain-free controls, which should be considered impossible considering that active MTPs are symptomatic by definition.
Until both consensus and reliability of diagnostic criteria for identifying MTPs are achieved and implemented in research studies, data on the validity, prevalence, aetiology and treatment of MTPs should be interpreted with prudence.
1. Tough EA, White AR, Richards S, Campbell J. Variability of criteria used to diagnose myofascial trigger point pain syndrome: Evidence from a review of the literature. Clinical Journal of Pain 2007;23:278-286.
2. Rickards LD. The effectiveness of non-invasive treatments for active myofascial trigger point pain: a systematic review of the literature. International Journal of Osteopathic Medicine 2006;9:120-136.
3. Myburgh C, Larsen AH, Hartvigsen J. A systematic, critical review of manual palpation for identifying myofascial trigger points: Evidence and clinical significance. Archives of Physical Medicine and Rehabilitation 2008;89:1169-1176.
4. Ettlin T, Schuster C, Stoffel R, Brüderlin A, Kischka U. A distinct pattern of myofascial findings in patients after whiplash injury. Archives of Physical Medicine and Rehabilitation 2008;89:1290-93.