Author's response to reviews Title: High prevalence of shoulder girdle muscles with myofascial trigger points in patients with shoulder pain. Authors:

Results subsection. I think the wording of the last sentence in the results section, though perhaps technically accurate English wording, could be misleading to the casual reader who might not read the article in depth. I think the authors should either term the correlation of number of muscles with active trigger points to DASH score as a “low-moderate” correlation, or preferably explicitly mention that the correlation found suggests the number of muscles in the shoulder girdle with active trigger points only explained about 10% of the patients’ shoulder pain symptoms as measured by the DASH score. This would provide the reader a more accurate and balanced interpretation of the data from the outset. Dr. Dorsher is fully correct when he mentions the low-moderate correlation between the number of shoulder muscles with MTrPs and the DASH score. For the interpretation of the correlation we used the classification of Feinstein (see section data-analysis). We agree with dr. Dorsher that 0.3 is the lowest value that is classified as moderate. We have added the word ‘only’ in the text to express our concerns that we share with dr. Dorsher about the low-moderate correlation. The first and second paragraphs of the Introduction that follows imply, correctly or not, that myofascial trigger points may be an important pathophysiologic cause of chronic non-specific shoulder pain, but this study’s data (which admittedly did not look at total number of trigger points in each muscle or their sensitivity) does not show presence of active trigger points to be any more predictive than depression score in terms of the patients’ DASH scores. We hypothesized that inflammation, degenerative changes, and impingement (in itself) do not explain shoulder pain. Therefore we were curious whether MTrPs could provide an alternative explanation for shoulder pain. To do this, the first step is to find out whether MTrPs are prevalent in a population of patients with shoulder pain, which was the primary aim of this study. The second step is to see whether MTrPs can predict pain and dysfunctioning by calculating the correlation and finally to look for the cause-effect relationship. We believe that there is enough evidence to state that myofascial trigger points can explain all kinds of musculoskeletal pain, including shoulder pain, but only few studies have been published about the impact of MTrPs on shoulder pain. The number of muscles with active MTrPs was only low-moderately correlated with the DASH score. High prevalence of shoulder girdle muscles with myofascial trigger points in patients with shoulder pain. To be clear that the focus of this paper is on the prevalence and not on the correlation we have changed the last sentence of the introduction section into: Further, the authors’ implication in their response that the number of trigger points in these muscles or their severity/sensitivity might better predict shoulder pain DASH scores does not seem to be corroborated by their data as Table 4 suggests finding active trigger points in the muscles studied only accounted for at most 11% of the VAS-P scores’ variance. Hopefully their other data in BMC Medicine will elucidate this. Again, we agree with dr. Dorsher about the low-moderate correlation between the number of shoulder muscles with active MTrPs and the DASH score, as we mentioned before. In the clinical trial that we published in January 2011 in BMC medicine, we were able to achieve clinical relevant results after 12 weeks of treatment and the number of shoulder muscles with MTrPs correlated positively with the DASH score at 12 weeks (r = 0.49; regression coefficient 2.15; p=0.000; ANOVA F = 9.6; p=0.000), which indicates that about 24% of the DASH score was predicted by the number of the shoulder muscles with MTrP. See http://www.biomedcentral.com/1741-7015/9/8 Introduction: Paragraph 3. Whether a twitch response (jump sign) (according to the textbooks, LTR and jump sign are considered to be different characteristics) is diagnostic of myofascial pain is questionable, as prior study by Sciotti et al had shown even experts had difficulty agreeing on the presence of this phenomenon. We fully agree with dr. Dosher about the diagnostic value of the LTR. But, although it is considered to be of diagnostic value when it is present, we have not used the twitch response as a diagnostic criterion. In a previous study we already reported the low interobserver agreement of the LTR. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2565638/ We have changed the text into: Did not see Figures 1a-d, only saw a Figure 1 in the revised paper and think the authors meant Figures 1-3 instead. Thanks, you are right and we have corrected this. The aim of this study was to determine the prevalence of MTrPs in a sample of patients presenting with chronic, non-traumatic unilateral shoulder complaints. Diagnostically, active MTrPs refer patient-recognized pain upon compression. Snapping palpation or needling can mediate a local twitch response in muscle fibers when stimulated, but its diagnostic value may be low. Materials and Methods Section 2.4 Table 1. Thank you for providing this table. I appreciate the authors’ comments on the levator scapula and serratus anterior as not directly causing shoulder pain, however if due to active or latent mTrPs those muscles are not activating properly to rotate the scapula, then does it not logically follow that abnormal substitution of other scapular stabilizers and rotator cuff musculature might cause development of trigger points (active or latent) in those muscles which will be difficult to treat long-term if the scapulothoracic abnormalities are not dealt with? The vast majority of the levator scapula’s referred pain (and the serratus anterior’s most concentrated pain) as described in the Trigger Point Manual is in the distribution of the “shoulder region” diagram provided by the authors, so I am still unsure why especially the levator scapula was not examined but I appreciate the authors’ perspective. We agree with dr. Dorsher that the levator scapulae muscle may be of great importance in patients with shoulder pain. We agree in particular, when he comments that MTrPs may have influence on the rotation of the scapula. Therefore it might be a good idea to include this muscle in future studies, but unfortunately, in this study we did not examine it. 2.4 The link to the DASH score produces an error message. We have tried to locate the error message but were unable to replicate the error message. 3 Results: Flowchart is now Figure 4 as labeled on the manuscript. We appreciate your bringing this to our attention and have corrected this. 3.1 might be more accurately worded “Prevalence of muscles with trigger points in subjects” since total number of trigger points was not ascertained, just the number of muscles with trigger points. We agree with dr. Dorsher that this is more accurate and have added ‘of shoulder muscles with’. 3.2 might be more accurately worded “Prevalence of myofascial trigger points by muscle” as the other wording suggests the authors are counting the number of trigger points in a given muscle. We have also changed this. 3.4 There is an error here as active trigger point correlation with DASH was 0.33 and not 0.44 as in the first sentence. Thank you. You are right. It is corrected in the text. The authors present only the most favorable data to their conclusion—the presence of MTrP “poorly” correlated (0.29) with DASH and the presence of active trigger point was only minimally better though termed “moderate”. This of course was not our intention to do so. Looking at table 4 we present the data from the primary outcome measure the DASH score, the three Visual Analogue Scales for Pain, the BDI-II, and the duration of complaints. In the text, we have only presented the correlation that could explain the impact of MTrPs on pain and functioning. The BDI, in our study, was used to exclude patients with major depression. The BDI scores were better predictors than the trigger point presence of DASH We agree with dr. Dorsher that the correlation of BDI scores and DASH was somewhat higher than the correlation between MTrPs and DASH. Although the scores may be correlated, this does not necessarily mean that one predicts the other. In other words, do patients with depression have more pain and limitations in functioning or are patients with pain and shoulder dysfunction more depressed. As the BDI scores were extremely low, this means that there were no patients with major depression (or even mild) and therefore we did not consider this to be relevant for this study. The negative correlation of latent trigger points to DASH scores is not reported. Although it was negative, the correlation was very small (-0.12). To our opinion this means no correlation instead of a relevant negative correlation. Again, I believe it would be more balanced data presentation if the fact that only 9% of the DASH score would be explained by presence of active trigger points in muscles studied to clarify the clinical significance of this “moderate” correlation found. The presence of muscles with active trigger points only explained 11% or less of the VAS-P scores variance, so I am interested to see if other data from the study in other publications shows multiple trigger points in muscles studied plus sensitivity helps explain a significant portion of the other 89% of the variance. We agree with you, but we have not studied sensitivity and multiple MTrPs. In future studies this would be very interesting to study. We have added the following line in the discussion section: “Figure 5” should be “Figure 8” in the last sentence. Thanks.You are right. Future studies of chronic shoulder pain examining the total number of MTrPs and their pressure sensitivity in the muscles studied could substantially impact the magnitude of the effect of presence of MTrPs on shoulder pain and disability. 4.3 It would be optimal if the first sentence specifically added at the end of the first sentence “including shoulder pain and disability”. That the active trigger point presence only explained 11% (r-square) of the subjects’ current pain and only 8% of their average pain over the past week would tend to counter the authors’ assertion that if the sensitivity of the active trigger points per Hidalgo had been studied the correlation of active trigger points and DASH scores might have been higher. We have added ‘and disability’ as you suggested. At this moment it is unclear whether adding the level of sensitivity to the number of MTrPs (and not the number of muscles) could influence the correlation. This is an interesting question for further research. The authors also don’t discuss at all the unexpected result that presence of latent trigger points had a negative correlation to DASH scores. If these latent trigger points presumably cause ROM restriction and subsequent dysfunction, how do the authors explain this negative correlation? All patients had normal to ‘only’ slightly limited range of motion. It is conceivable that this had no influence on the DASH score as a slight PROM restriction has no relevant influence on daily functioning or pain and therefore it will not influence the DASH score. We consider this slight PROM restriction more as a clinical sign and not as a patient reported complaint. It is obvious that with a fixed number of muscles (17 muscles) that are examined, that more latent MTrPs result in less active MTrPs (r= 0.64), and active MTrPs are responsible for spontaneous pain and latent are not. Would more trigger points found in those 17 muscles that had negative correlation or weak positive correlation increased the prediction of DASH score? Dr. Dosher puts forward a very interesting question, but based on our current study, we cannot render any conclusion. It would, however be an interesting subject for future studies. The correlations of active trigger points and latent trigger points to duration of symptoms were extremely weak (0.12 and 0.04, respectively). Possibly, but the weak correlations make that a very uncertain claim. We would like to comment on this, but is not clear to which claim the reviewer is referring. We do not believe we made any specific claim in this context. The authors don’t even mention the BDI scores which correlated to the DASH scores better (though still weakly) than the presence of active or latent trigger points. The BDI is not developed as an outcome measure. It is developed and used to discriminate between several stages of depression and in our study to exclude patients with a major depression. My concern about this is that the discussion in this section does not report results that are not favorable to a conclusion that trigger points are an important clinical cause of chronic shoulder pain, and the discussion seems to be trying to justify why the correlation of active trigger points to DASH scores is weak (9% of variance of DASH score) instead (presumably from lack of mTrP intensity measures and number of mTrP per muscle in the present study). Our primary aim was to study the prevalence of shoulder muscles with MTrPs in patient with shoulder pain. We agree with you that the number of muscles with (one or more) MTrPs does not correlate well with the DASH. In section 4.3, we have discussed the possible reasons for this finding. We have mentioned that we have not measured the Pressure Pain Threshold or the number of MTrPs in each muscle. Furthermore, we have discussed the limitations of the DASH outcome score, as this measurement tool does not discriminate between the affected and non-affected arm. At the other hand, it is still obvious that in every patient with shoulder pain we were able to elicit the familiar shoulder pain by firmly pressing on one or more ‘active’ MTRPs (which is pain producing by definition). To this end, I think the last sentence should have said “Though the presence of active trigger points in muscles studied only accounted for 9% of the variance of the shoulder pain and disability as measured by DASH scores and latent trigger points none of that score’s variance, this does not mean that that trigger points are not clinically important. Future studies of chronic shoulder pain examining the total number of trigger points and their pressure sensitivity in the muscles studied could substantially impact the magnitude of the effect of presence of myofascial trigger points on shoulder pain and disability.” We have added the sentence to the text. 4.4 Again this section appears to overstate the significance of the present studies findings by implying active trigger points are an alternative explanation for non-specific shoulder pain despite the weak correlations (9% variance found). The authors discuss importance of latent trigger points yet never comment that their study found a negative correlation between presence of latent trigger points and DASH score (presence of latent trigger points improves shoulder function or at least does not influence it). Thus, I think the data does not support the conclusions of paragraphs 3 and 4 in this section that trigger point therapy should precede most other commonly practiced interventions for shoulder pain. We have tried to formulate the conclusions very carefully, based on the high prevalence of pain producing MTRPs (‘ If MTrPs are one of the main reasons for shoulder pain.......then anti-inflammatory treatment and muscle strengthening exercises should not be the treatment of first choice.’ and ‘If the above hypothesis is acceptable, the treatment could provide an innovative, promising therapy for shoulder pain.’). 5 Conclusion I think given the issues with the weak correlation of presence of active trigger points (r2=0.09) with DASH and pain scores, the “poor” correlation of mTrPs (r=0.29) with DASH scores, and the negative to near zero correlation of presence of latent trigger points with DASH and pain scores, the present conclusion is still misleading to the casual reader and tends to overstate the magnitude of the potential clinical importance of the presence of trigger points in shoulder pain, at least as far as the present data provides, nor does the present data provide compelling evidence that trigger point therapy should be more a first line treatment than NSAID or PT interventions. The message of this paper is that there is a high prevalence of MTrPs. We have mentioned a number of reasons that may explain the moderate correlation. It is a challenge for future research to search for other factors that may help to explain shoulder pain. Whether these factors are related to MTrPs or not is still unclear. Hopefully future studies with total number of trigger points and/or their sensitivity might enhance the correlations with DASH and VAS but the weak correlations noted in the present data of presence of active trigger points and VAS scores and symptom duration make even that outcome uncertain. We agree with dr. Dosher that it would be desirable to include these recommendations in future research.