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New Views of Myofascial Trigger Points: Etiology and Diagnosis

      Abstract

      Simons DG. New views of myofascial trigger points: etiology and diagnosis.
      Two studies appearing in Archives, one by Shah and colleagues and another one by Chen and colleagues, present groundbreaking findings that can reduce some of the controversy surrounding myofascial trigger points (MTPs). Both author groups recognize the ubiquity of this disease and the importance to patients of health care professionals becoming better acquainted with the cause and identification of MTPs. The integrated hypothesis is the most credible and most complete proposed etiology of MTPs. However, the feedback loop suggested in this hypothesis has a few weak links, and studies by Shah and colleagues in particular supply a solid link for one of them. The feedback loop connects the hypothesized energy crisis with the milieu changes responsible for noxious stimulation of local nociceptors that causes the local and referred pain of MTPs. Shah’s reports quantify the presence of not just 1 noxious stimulant but 11 of them with outstanding concentrations of immune system histochemicals. The results also strongly place a solid histochemical base under the important clinical distinction between active and latent MTPs. The study by Chen on the use of magnetic resonance elastography (MRE) imaging of the taut band of an MTP in an upper trapezius muscle may open a whole new chapter in the centuries-old search for a convincing demonstration of the cause of MTP symptoms. MRE is a modification of existing magnetic resonance imaging equipment, and it images stress produced by adjacent tissues with different degrees of tension. This report seems to present an MRE image of the taut band that shows the chevron signature of the increased tension of the taut band compared with surrounding tissues.

      Key Words

      TWO RECENT GROUND-BREAKING articles published in Archives cast our understanding and clinical diagnosis of myofascial trigger points (MTPs) into a new light. The first article, by Shah et al,
      • Shah J.P.
      • Phillips T.M.
      • Danoff J.V.
      • Gerber L.H.
      An in vivo microanalytical technique for measuring the local biochemical milieu of human skeletal muscle.
      published in this issue of Archives uses an unprecedented, most ingenious, and technically demanding technique for sampling the histochemical milieu of MTPs. The results strongly substantiate an essential step in the integrated hypothesis
      • Simons D.G.
      Review of enigmatic MTrPs as a common cause of enigmatic musculoskeletal pain and dysfunction.
      of the etiology of MTPs, enhancing the light shining on our understanding of the nature and etiology of MTPs. A 2005 Shah article published elsewhere and the follow-up,
      • Shah J.P.
      • Danoff J.V.
      • Desai M.J.
      • et al.
      Biochemicals associated with pain and inflammation are elevated in sites near to and remote from active myofascial trigger points.
      published here, should help to reduce the controversy concerning the nature of MTPs.
      The other article, by Chen et al,
      • Chen Q.
      • Bensamoun S.
      • Basford J.R.
      • Thompson J.M.
      • An K.N.
      Identification and quantification of myofascial taut bands with magnetic resonance elastography.
      raises the prospect of a clinically available method for imaging evidence of an MTP. This is a development that the MTP field has sorely needed until now. The imaging technique could make a substantial difference in the acceptance of the reality and importance of MTPs by mainstream medicine. This would provide enormous benefit in the alleviation of patient suffering and in the improvement in the effectiveness of our excessively expensive health care system by eliminating untold unnecessary diagnostic procedures.

      Validation of the Integrated Hypothesis

      The Shah Studies

      The 2 articles by Shah
      • Shah J.P.
      • Phillips T.M.
      • Danoff J.V.
      • Gerber L.H.
      An in vivo microanalytical technique for measuring the local biochemical milieu of human skeletal muscle.
      • Shah J.P.
      • Danoff J.V.
      • Desai M.J.
      • et al.
      Biochemicals associated with pain and inflammation are elevated in sites near to and remote from active myofascial trigger points.
      represent unprecedented, ground-breaking progress toward the acceptance and incorporation of MTPs into mainstream medicine. Commonly, authors say that the etiology of MTPs is unknown. The integrated hypothesis
      • Simons D.G.
      Review of enigmatic MTrPs as a common cause of enigmatic musculoskeletal pain and dysfunction.
      epitomizes the most credible explanation of the etiology that has been proposed to date. It has stood the test of time since it was introduced in 1999
      • Simons D.G.
      • Travell J.G.
      • Simons L.S.
      Travell & Simons’ myofascial pain and dysfunction: the trigger point manual. Vol 1.
      and has gained stature since then. The hypothesis has a weak link in the connection between the energy crisis in the vicinity of the affected endplate and the noxious histochemicals that stimulate nearby nociceptors. These noxious histochemicals were proposed to account for the pain associated with active MTPs. There were many known candidates,
      • Mense S.
      • Simons D.G.
      • Russell I.J.
      Muscle pain: understanding its nature, diagnosis, and treatment.
      but none had been shown experimentally. The 2 Shah studies effectively fill that gap, and they add important substantiation to the hypothesis.
      In both studies, Shah
      • Shah J.P.
      • Phillips T.M.
      • Danoff J.V.
      • Gerber L.H.
      An in vivo microanalytical technique for measuring the local biochemical milieu of human skeletal muscle.
      • Shah J.P.
      • Danoff J.V.
      • Desai M.J.
      • et al.
      Biochemicals associated with pain and inflammation are elevated in sites near to and remote from active myofascial trigger points.
      describes a most ingenious and technically very demanding technique for sampling the histochemical milieu of MTPs and what it revealed. These studies were outstandingly well designed, distinguishing active and latent MTP effects in different groups of subjects plus a control group free of MTPs. The second study
      • Shah J.P.
      • Danoff J.V.
      • Desai M.J.
      • et al.
      Biochemicals associated with pain and inflammation are elevated in sites near to and remote from active myofascial trigger points.
      doubled the number of subjects, added comparable data from an MTP-free gastrocnemius remote muscle, and analyzed 2 new endocrine biochemicals. The published curves tell the story far more eloquently and convincingly than just statistical significance, which was also impressive.

      The 2005 study

      The first study
      • Shah J.P.
      • Phillips T.M.
      • Danoff J.V.
      • Gerber L.H.
      An in vivo microanalytical technique for measuring the local biochemical milieu of human skeletal muscle.
      in 2005 reported graphs of dramatic and unexpected results that consistently started at baseline on the placement of the needle and retained their initial relationship before, during, and after a local twitch response was elicited in the upper trapezius. These similar and clear graphs in 9 subjects were far more convincing, impressive, and informative than a study that requires dozens of subjects to reach statistical significance.
      The 2005 study revealed some surprising, previously unknown, features of MTPs. Instead of just a few noxious chemicals that stimulate nociceptors, nearly everything that has that effect was present in abundance. In addition, the milieu is strongly acidic. The amount of these substances was very significantly and consistently greater in active MTPs than latent ones. The fact that essentially all of them present with a stable baseline before the local twitch response confirms that the observations are because of the nature of the milieu and not just a needle-insertion artifact. The shift in pH was something Janet Travell, MD,
      • Simons D.G.
      • Travell J.G.
      • Simons L.S.
      Travell & Simons’ myofascial pain and dysfunction: the trigger point manual. Vol 1.
      anticipated, and it intensifies the painfulness of the MTPs.
      The elevation in noxious substances was consistently and significantly greater for active MTPs than for latent MTPs, which was slightly but consistently more than in MTP-free muscles. This unexpected result puts a solid research basis under the definitions of active and latent MTPs that started as a purely clinical distinction of convenience. The 2 have only 1 clear clinical diagnostic difference. Active MTPs elicit pain when pressed that the patient recognizes as familiar. Latent MTPs cause no clinical pain complaint so the pain is not familiar to patients, but when the MTPs are pressed, they may elicit referred pain characteristic of that muscle. The active MTPs are what bring patients in for relief and must be addressed for patient satisfaction. Latent MTPs, as is now becoming quite clear based on book chapters and mostly unpublished surface electromyographic studies, can powerfully disturb normal motor function (excitation, inhibition, coordination), not only in the same muscle but also in functionally related muscles. One credible research study
      • Lucas K.R.
      • Polus P.A.
      • Rich J.
      Latent myofascial trigger points: their effect on muscle activation and movement efficiency.
      has been published that emphasizes the importance of consistently making a clear clinical distinction between active and latent MTPs.
      The marked elevation of histochemicals during the local twitch response was followed by a slow, variable return to baseline or an overshoot to below baseline that was specific to the analyte examined.
      That immune system chemicals were the most significantly increased histochemicals was unexpected, although Travell
      • Simons D.G.
      • Travell J.G.
      • Simons L.S.
      Travell & Simons’ myofascial pain and dysfunction: the trigger point manual. Vol 1.
      called attention to the clinical fact that active allergies strongly perpetuate MTPs. Also, a physiology study published in 1974
      • Ito Y.
      • Miledi R.
      • Vincent A.
      Transmitter release induced by a ‘factor’ in rabbit serum.
      described a large increase in acetylcholine (ACh) release when frogs were injected with rabbit serum. That was interpreted as immune system upmodulation of endplate ACh release. Increased ACh release is part of the integrated hypothesis.
      • Simons D.G.
      Review of enigmatic MTrPs as a common cause of enigmatic musculoskeletal pain and dysfunction.

      The current study

      The second study by Shah,
      • Shah J.P.
      • Danoff J.V.
      • Desai M.J.
      • et al.
      Biochemicals associated with pain and inflammation are elevated in sites near to and remote from active myofascial trigger points.
      in addition to repeating the first study, doubled the number of subjects, reinforced its findings, recorded the biochemical milieu of the uninvolved gastrocnemius muscle, and added analysis of 2 more biochemicals. Samples were tested for 10 substances by using, as before, immunocapillary electrophoresis and capillary electrochromatography. A microdialysis needle was inserted into the acupuncture point B-21 to standardize the procedure. (This is a pain acupuncture point, which is also an MTP location that was confirmed here by local twitch responses. This identity was shown for another classical pain acupuncture site by others.
      • Hong C.Z.
      Myofascial trigger point pathophysiology and correlation with acupuncture points.
      ) The needle remained stationary for 1 minute before starting sample collections either every minute or every 20 seconds. At 5 minutes, the needle was advanced to elicit a local twitch response in subjects with MTPs that was confirmed by surface electromyography and is diagnostic of an MTP. Equivalent needle insertions were used in subjects who were without a local twitch response. Another microdialysis needle was inserted into the calf muscle and left in place undisturbed and sampled every minute.
      Samples were analyzed immediately for pH; bradykinin; substance P; calcitonin gene-related peptide; tumor necrosis factor α; interleukin 1β (IL-1β), IL-6, and IL-8; serotonin; and norepinephrine. Analysis of IL-6 and IL-8 is new to this second study.
      Subjects with active MTPs compared with the other 2 groups reported lower visual analog scale readings (more pain) (P<.001) and also had greater sensitivity to pain pressure threshold measurements that were clinically but not statistically significant. The results of analyte analysis of the 2005 study were in close agreement with those of the current Shah study and showed no statistical difference.
      As before, all analyte concentrations were higher in active than in latent or normal subjects (P<.002), but they were always higher (pH did not differ) than concentrations in the gastrocnemius. This degree of increase and elevation in the uninvolved gastrocnemius muscle of all analytes for subjects with either active trapezius MTP compared with normative values in MTP-free subjects suggests that substances associated with pain and fatigue are not limited to MTP locations.
      The increase in analytes in the trapezius in response to a local twitch response was not seen in the gastrocnemius, indicating that the increases in the uninvolved muscle depend on a more sustained sensory input from the active MTP in the trapezius. This suggests that a component of central sensitization is involved in the gastrocnemius elevations.
      The biochemical changes fully explain the local tenderness and pain referred from MTPs. The changes support the previous finding
      • Brückle W.
      • Suckfüll M.
      • Fleckenstein W.
      • Weiss C.
      • Müller W.
      [Tissue pO2 measurement in taut back musculature (m. erector spinae)].
      that there is severe hypoxia in the vicinity of an MTP that would result from the ischemia evidenced in biopsies
      • Fassbender H.G.
      Non-articular rheumatism.
      and increased energy demand from the sarcomere shortening of taut bands to producing a local energy crisis. This study strongly substantiates the integrated hypothesis.
      Reinforcing the initial observation, the increased amounts of the 2 additional immune factors in this study emphasize the unexpected importance of immune factors to MTPs. This new understanding of immune system involvement deserves serious clinical consideration and research investigation.
      Also noteworthy is the surprising observation that baseline acidity, substance P, and norepinephrine are as increased in the uninvolved remote gastrocnemius muscle as at the MTP. That this is not a technical error is shown by the equally surprising lack of any elevation in bradykinin in the gastrocnemius.

      Imaging to Confirm the Presence of a Myofascial Trigger

      This study by Chen et al
      • Chen Q.
      • Bensamoun S.
      • Basford J.R.
      • Thompson J.M.
      • An K.N.
      Identification and quantification of myofascial taut bands with magnetic resonance elastography.
      is a ground-breaking first. Although previous authors have investigated muscle by using magnetic resonance elastography (MRE), this is the first study that specifically examined imaging of the MTP phenomena. Chen focused on the imaging of taut bands of MTPs because of the high prevalence and clinical importance of that disease. The possibility of imaging taut bands promises to open up a whole new chapter in the MTP saga. Finding a taut band by palpation requires considerable skill that is a combination of innate palpation skill (something many clinicians were not blessed with), authoritative training, and critical clinical practice as is required for any advanced medical skill, such as heart surgery. Finding just the tender spot of an MTP is much simpler. If the clinician makes use of the published pain patterns of individual muscles, the patient’s pain complaint gives a running start as to which muscles to examine. When range of motion is painfully limited, the patient can usually point to the painful muscle; this provides more help to the practitioner. The muscle with an MTP is usually similarly painful when contracted in the shortened position. Then all the clinician must do is poke the suspected muscle(s) with a finger to find an exquisitely tender spot. Rheumatologists are quite practiced at this kind of procedure to diagnose fibromyalgia and are perplexed by taut bands for identifying MTPs. A request to the local radiology department equipped with MRE (and a number are already) is all that would be needed to confirm the diagnosis for the benefit of all, including the third-party payer and payment. This indeed shows promise for the dawning of a new day for the disease of MTPs.
      Although this study presented many new findings, I have some concerns. In the methods section, the diagnostic criteria used to identify the MTP was unsatisfactory. To me, the statement that “the diagnosis [was] confirm[ed] by a physician experienced in its diagnosis and treatment”
      • Chen Q.
      • Bensamoun S.
      • Basford J.R.
      • Thompson J.M.
      • An K.N.
      Identification and quantification of myofascial taut bands with magnetic resonance elastography.
      (p1659) is meaningless. I have reviewed too many studies in which the examiner presented as an expert, but the diagnostic criteria were not stated, and the rest of the study made it clear that the examiner used poor examination criteria and technique that resulted in misleading if not nonsensical results.
      Fortunately, the introduction mentions that a main finding for MTPs is localized taut bands with points of tenderness that were more circumscribed than the band and when compressed (the MTP) produce stereotypical referred pain patterns in contrast to fibromyalgia tender points. These findings were likely included as diagnostic criteria on initial examination; I hope so. I also hope that Chen and others will do better than in this study in the future. Until there is a generally accepted set of diagnostic criteria, it is critically important that every MTP research study explicitly and completely describe the examination used to identify the MTPs because there is so much variation in criteria used among different researchers.
      • Tough E.A.
      • White A.R.
      • Richards S.
      • Campbell J.
      Variability of criteria used to diagnose myofascial trigger point pain syndrome—evidence from a review of the literature.
      MRE is an advancement in magnetic resonance imaging (MRI) that uses phase-contrast imaging to image differences in tissue stiffness. Contracted muscle fibers feel harder because they are stiffer than relaxed fibers. Vibration must be applied to the muscle to induce cyclic shear waves, which are imaged by phase-contrast analysis. From this, the wavelength is measured, which reveals the speed of transmission. Then, the shear modulus is calculated and imaged.
      Adding MRE capability to the conventional MRI is relatively simple. The computer analysis to produce either image must include the additional calculation to determine shear wave modulus. Also, a device is needed that induces cyclic mechanical vibrations in the muscle. A simple single-frequency mechanical vibrator has proven effective, but the audio device described here has 2 advantages. It can stimulate a larger area of muscle and has the potential to adjust the frequency of vibration.
      The validity of this method was pretested in 2 ways that are clearly described. The bovine gel phantom was tested with MRE. It was designed with homogeneous gel, and the results appear in figure 2A. The image obtained with a strip of stiffer gel to simulate a taut band appears in figure 2B with a chevron pattern. The finite element simulation using different simulation material was also imaged to validate this technique. The greater velocity of propagation of the mechanical waves in the simulated taut band compared with the surrounding less stiff material produced shear waves that again recorded with a chevron pattern (fig 2D).
      The control subject had no history or findings of MTPs. The patient had a 3-year history of myofascial pain, and the physician, experienced in the diagnosis and treatment of myofascial pain, marked the position of a right-upper trapezius taut band with an indelible marker. The MRE of the trapezius of the control in figure 2E clearly corresponds to the images of figures 2A and 2C.
      Figure 2F is the point of the study and, unfortunately, the published image is too small to see details clearly, has labels that are difficult to follow, and has an incomplete legend. To me, it seems as if the white line running diagonally between the upper left and lower right corners of the figure identifies the location and direction of the clinically determined taut band. The white band marked with a square bracket and labeled III is probably the MRE band with a chevron of which there apparently is only one and is not as distinct as in the phantoms. There are likely ways in which the clarity of this finding can be enhanced.
      One likely possibility is to explore the fact that the degree of muscle tension determines its resonant frequency.
      • Simons D.G.
      • Mense S.
      Understanding and measurement of muscle tone related to clinical muscle pain.
      It should be possible to tune the mechanical stimulator for resonance in an individual muscle to either the resonant frequency of the taut band or the surrounding less tense muscle, maximized by this difference in tension. The difference in the frequencies (Hz) should reflect the relative tension of the taut band. Like a newborn baby, this development has unknown potential that depends strongly on the nurture and attention it receives.

      Conclusions

      I hope that these 2 studies
      • Shah J.P.
      • Danoff J.V.
      • Desai M.J.
      • et al.
      Biochemicals associated with pain and inflammation are elevated in sites near to and remote from active myofascial trigger points.
      • Chen Q.
      • Bensamoun S.
      • Basford J.R.
      • Thompson J.M.
      • An K.N.
      Identification and quantification of myofascial taut bands with magnetic resonance elastography.
      will encourage those responsible for medical student and resident training to incorporate the diagnosis and treatment of MTPs into their curricula more fully. It should be self-evident that treating the cause of pain and teaching patients how to control it for themselves with manual methods is much better than simply treating the pain symptom with drugs or inactivating pain pathways with injection procedures. Teaching this subject, however, is a demanding proposition that involves more than just MTPs. These articles only present convincing evidence as to why it is important for medical educators to get the training and to take time with their patients to develop the necessary skills to teach their students.
      Even with MRE imaging of taut bands, it will still be necessary to be able to locate the MTPs by examining patients so orders can be written for appropriate MRE examinations and for treating them. Skilled therapists can do the treatment after the diagnosis has been entertained. Currently, consideration of the possibility of an MTP component of the pain complaint is commonly not effectively included in the differential diagnosis and therefore is missed cold turkey, which can be very expensive for the health care system (expensive examinations looking for a phantom diagnosis) and disastrous to the patient (wrong diagnosis, wrong treatment).

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