Comment on: A critical evaluation of the trigger point phenomenon

S ir , We read the article by Quinter et al. [ 1 ] with great interest. They present an overview of the ever-evolving, clinically important topic of myofascial trigger points (MTrPs). In general, we would agree with the ideas they present of the theoretical origins of the MTrPs, and that very little work has been done to advance the science thus far regarding their existence and the processes that maintain them [ 2 , 3 ]. We find ourselves unable, however, to agree with their assessment that ‘All working hypotheses derived from this conjecture have been refuted and therefore the theory can be discarded’ [ 1 ]. We agree that the physical assessment of trigger points is inconsistently done and that the literature that examines the inter-rater reliability of the palpation of MTrPs is of unacceptably low quality [ 3 , 4 ]. This is due to methodological variability and weaknesses such as small sample size, lack of predetermined cutpoint for the kappa statistic, poor blinding of subjects and examiners, inadequate numbers of examiners, and inadequate training and standardization of the palpation technique utilized in the studies [ 5 , 6 ]. While we address the specific issues regarding the clinical phenomena, our position in this commentary is that the trigger point is central to the diagnosis of myofascial pain syndrome, but that a clinically thorough diagnosis must incorporate additional parameters. Reproducibility of detection of the MTrP in this context is not, strictly speaking, confined to the skill of manual palpation. In fact, only the identification of the taut band is a purely palpatory skill. The other criteria are either observations (local twitch response and jump sign), established through patient feedback (pain referral and patient pain recognition), or are a hybrid (local tenderness is palpated but confirmed by patient feedback). Therefore, palpation, observation and patient feedback combine during the trigger point examination to influence examiner judgement. If reproducibility studies do not reflect this complex amalgamation of interactions clearly, study designs are likely to continue to produce inconsistent findings. Use of standard diagnostic procedures should provide a scientific basis for reproducibility of detection of MTrPs. None of the studies available for review considered these phenomena together and are therefore prone to variability and error. In addition, the difference in severity between subjects used for a reliability study also needs to be taken into account or study results will be different. Also, with repeated examinations, the severity of pain, patient grimacing and withdrawal are expected to change. These factors were also not commented upon in the studies reviewed. Therefore, the research to date can be interpreted as inconclusive with respect to the reliability of detection of the MTrP. This, however, does not mean that MTrPs do not exist—the problem may well be inadequate study design and power. A study that addresses all of the above issues is urgently required to settle the issue. With respect to biochemical analyses of the MTrP, the study quoted in the article is criticized because mediators were also detected in unrelated muscles. There were also significantly different levels between the sites. This also ignores the very reasonable explanations that Shah and Gilliam [ 7 ] offered in their review: the elevated levels in the unrelated muscles are a consequence of central sensitization (due in part to the MTrP), or inadequate clearing of these metabolites may predispose to the development of active MTrPs. In addition, it is not mentioned that substance P and calcitonin gene-related peptide (CGRP) levels fell after sampling, supporting the theoretical underpinnings of dry needling as a treatment via dispersal of the MTrP to reduce pain. Our review of the literature suggests that there is a biochemical underpinning, but this needs further exploration through scientifically sound research. The section on US considers only two studies, but there are many others. There has been no consensus on the findings because there has been a wide range of reported echogenic, size and Doppler characteristics. There are a number of reasons for this, including small sample size, lack of control for the acuity of the MTrP and lack of standardization of US probes and scanning techniques. However, research has provided promising results: 81% specificity and 69% sensitivity in discriminating active MTrPs from normal muscle [ 8 ]. Again, further research is necessary in order to define the US characteristics of the MTrP. We would also like to emphasize that both the biochemical and US evidence we consider above suggests several objective differences between active and latent trigger points in opposition to the claim that latent MTrPs are invented merely to explain MTrP presence in muscles not exhibiting clinical symptoms. In summary, the field is in its infancy and much more work needs to be done with robust standard methodological procedures to define the physical examination, US and biochemical characteristics of the MTrP. Once established, the standard procedures used need prospective validation for feasibility and reliability. This would help to establish composite diagnostic criteria and allow study of physiotherapeutic and pharmacotherapeutic treatments. Funding : No specific funding was received from any funding bodies in the public, commercial or not-for-profit sectors to carry out the work described in this manuscript. Disclosure statement : The authors have declared no conflicts of interest.

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