Increase in muscle nociceptive substances and anaerobic metabolism in patients with trapezius myalgia: microdialysis in rest and during exercise

Topical review - salivary biomarkers in chronic muscle pain

BACKGROUND AND AIMS

Muscle related temporomandibular disorders (myogenous TMD), one of the most common orofacial pain conditions, is characterized by facial pain and often accompanied by jaw movement limitations. Although the underlying biological mechanisms are still unclear, a cluster of proteins and peptides is assumed to be involved in the pathophysiology. These proteins and peptides may be measured in a simple non-invasive saliva sample. This work investigated whether saliva can be used to sample algogenic substances that can serve as molecular biomarkers for TMD myalgia.

METHODS

Saliva and blood samples were collected from healthy individuals (n=69) and patients diagnosed with TMD myalgia (n=39) according to the Diagnostic Criteria for TMD. Unstimulated and stimulated whole, parotid, and sublingual saliva were analysed. The protein profiles were investigated using two-dimensional gel electrophoresis followed by identification with liquid chromatography tandem mass spectrometry. Levels of nerve growth factor (NGF), calcitonin gene-related peptide (CGRP), and brain derived neuro-tropic factor (BDNF) were determined using western blotting based technology and multiplex electro-chemiluminescence assay panel. Glutamate, serotonin, and substance p (SP) were determined using commercially available methods.

RESULTS

Different saliva collection approaches resulted in significant differences in the protein profile as well as in the expression of NGF, BDNF, CGRP, SP, and glutamate. Stimulated whole saliva showed least variability in protein concentration (35%) and was correlated to plasma levels of glutamate. Unlike SP and glutamate, NGF and BDNF expressed a rhythmic variation in salivary expression with higher levels in the morning (p<0.05). Patients with a diagnosis of TMD myalgia had significantly higher levels of salivary glutamate but lower salivary NGF and BDNF compared to controls; in addition, the lower NGF and BDNF levels correlated to psychological dysfunction. The quantitative proteomics data revealed 20 proteins that were significantly altered in patients compared to controls. The identified proteins are involved in metabolic processes, immune response, and stress response. Dissimilarities in protein profile and clinical variables were observed between TMD myalgia and myofascial pain.

CONCLUSIONS

The work highlights the importance of consistency in saliva collection approaches, including the timing of the collection. It displayed significant changes in pain specific mediators and protein profile in TMD myalgia and furthermore dissimilarities between subclasses indicating different pathophysiology. After extensive validation, potential salivary biomarkers can be combined with clinical features to better understand and diagnose TMD myalgia.

Fibromyalgia: Associations Between Fat Infiltration, Physical Capacity, and Clinical Variables

Background

Obesity is a risk factor for the development of fibromyalgia (FM) and generally most studies report increased Body Mass Index (BMI) in FM. Obesity in FM is associated with a worse clinical presentation. FM patients have low physical conditioning and obesity further exacerbates these aspects. Hitherto studies of FM have focused upon a surrogate for overall measure of fat content, ie, BMI. This study is motivated by that ectopic fat and adipose tissues are rarely investigated in FM including their relationships to physical capacity variables. Moreover, their relationships to clinical variables including are not known. Aims were to 1) compare body composition between FM and healthy controls and 2) investigate if significant associations exist between body composition and physical capacity aspects and important clinical variables.

Methods

FM patients (n = 32) and healthy controls (CON; n = 30) underwent a clinical examination that included pressure pain thresholds and physical tests. They completed a health questionnaire and participated in whole-body magnetic resonance imaging (MRI) to determine body composition aspects.

Results

Abdominal adipose tissues, muscle fat, and BMI were significantly higher in FM, whereas muscle volumes of quadriceps were smaller. Physical capacity variables correlated negatively with body composition variables in FM. Both body composition and physical capacity variables were significant regressors of group belonging; the physical capacity variables alone showed stronger relationships with group membership. A mix of body composition variables and physical capacity variables were significant regressors of pain intensity and impact in FM. Body composition variables were the strongest regressors of blood pressures, which were increased in FM.

Conclusion

Obesity has a negative influence on FM symptomatology and increases the risk for other serious conditions. Hence, obesity, dietary habits, and physical activity should be considered when developing clinical management plans for patients with FM.

Myofascial Treatment for Microcirculation in Patients with Postural Neck and Shoulder Pain

Vascular impairment is a crucial factor associated with chronic muscle pain, but relevant research from the microcirculatory aspect is lacking. Here, we investigated the differences in neck muscle microcirculation detected through laser-doppler flowmetry (LDF) and cervical biomechanics by a videofluoroscopic image in asymptomatic participants and patients with postural neck and shoulder pain. To understand the mechanism behind the effect of myofascial treatment, transverse friction massage (TFM) was applied and the immediate effects of muscular intervention on microcirculation were monitored. In total, 16 asymptomatic participants and 22 patients (mean age = 26.3 ± 2.4 and 25.4 ± 3.2 years, respectively) were recruited. Their neck muscle microcirculation and spinal image sequence were assessed. The differences in the baseline blood flow between the asymptomatic and patient groups were nonsignificant. However, the standard deviations in the measurements of the upper trapezius muscle in the patients were significantly larger (p < 0.05). Regarding the TFM-induced responses of skin microcirculation, the blood flow ratio was significantly higher in the patients than in the asymptomatic participants (p < 0.05). In conclusion, postintervention hyperemia determined through noninvasive LDF may be an indicator for the understanding of the mechanism underlying massage therapies and the design of interventions for postural pain.

An ergonomic welding torch reduces physical load response and improves welding quality in novices: a pilot study

Objectives. This crossover pilot study aimed to compare the physical load response of an ergonomically improved welding torch versus a conventional torch. Methods. Ten inexperienced volunteers performed an experimental augmented virtual welding trial at chest height (ASME code 1G) and overhead (ASME code 4G) with both welding torches in random order. Skeletal muscle load and fatigue were assessed by surface electromyography and changes in isometric peak force. The sensation of pain, perceived exertion and welding execution quality were defined as further outcome parameters. Results. The muscle load response in three out of eight muscles was lower in favour of the ergonomic welding torch, which went along with a lower sensation of pain and a higher working accuracy. Conclusions. An ergonomically improved welding torch reduces the acute physical load response and sensation of pain, which ultimately allows performing better, and might contribute to prevention of musculoskeletal diseases in the long term.

Does the Interaction between Local and Systemic Inflammation Provide a Link from Psychology and Lifestyle to Tissue Health in Musculoskeletal Conditions?

Musculoskeletal conditions are known to involve biological, psychological, social and, often, lifestyle elements. However, these domains are generally considered in isolation from each other. This siloed approach is unlikely to be adequate to understand the complexity of these conditions and likely explains a major component of the disappointing effects of treatment. This paper presents a hypothesis that aims to provide a foundation to understand the interaction and integration between these domains. We propose a hypothesis that provides a plausible link between psychology and lifestyle factors with tissue level effects (such as connective tissue dysregulation/accumulation) in musculoskeletal conditions that is founded on understanding the molecular basis for interaction between systemic and local inflammation. The hypothesis provides plausible and testable links between mind and body, for which empirical evidence can be found for many aspects. We present this hypothesis from the perspective of connective tissue biology and pathology (fibrosis), the role of inflammation locally (tissue level), and how this inflammation is shaped by systemic inflammation through bidirectional pathways, and various psychological and lifestyle factors via their influence on systemic inflammation. This hypothesis provides a foundation for new consideration of the development and refinement of personalized multidimensional treatments for individuals with musculoskeletal conditions.

Peripheral glutamate receptor and transient receptor potential channel mechanisms of craniofacial muscle pain

Temporomandibular joint disorder is a common chronic craniofacial pain condition, often involving persistent, widespread craniofacial muscle pain. Although the etiology of chronic muscle pain is not well known, sufficient clinical and preclinical information supports a contribution of trigeminal nociceptors to craniofacial muscle pain processing under various experimental and pathological conditions. Here, we review cellular and molecular mechanisms underlying sensitization of muscle nociceptive afferents. In particular, we summarize findings on pronociceptive roles of peripheral glutamate in humans, and we discuss mechanistic contributions of glutamate receptors, including N-methyl-D-aspartate receptors and metabotropic glutamate receptors, which have considerably increased our understanding of peripheral mechanisms of craniofacial muscle pain. Several members of the transient receptor potential (TRP) family, such as transient receptor potential vanilloid 1 (TRPV1) and transient receptor potential ankyrin 1, also play essential roles in the development of spontaneous pain and mechanical hypersensitivity in craniofacial muscles. Furthermore, glutamate receptors and TRP channels functionally and bi-directionally interact to modulate trigeminal nociceptors. Activation of glutamate receptors invokes protein kinase C, which leads to the phosphorylation of TRPV1. Sensitization of TRPV1 by inflammatory mediators and glutamate receptors in combination with endogenous ligands contributes to masseter hyperalgesia. The distinct intracellular signaling pathways through which both receptor systems engage and specific molecular regions of TRPV1 are offered as novel targets for the development of mechanism-based treatment strategies for myogenous craniofacial pain conditions.

Patients with episodic migraine show increased T2 values of the trapezius muscles - an investigation by quantitative high-resolution magnetic resonance imaging

Background

Neck pain is frequent in patients with migraine. Likewise, evidence for inflammatory processes in the trapezius muscles is accumulating. However, non-invasive and objectively assessable correlates are missing in vivo.

Methods

Twenty-one subjects with episodic migraine (mean age: 24.6 ± 3.1 years, 18 females) and 22 controls (mean age: 23.0 ± 2.2 years, 17 females) without any history of headache prospectively underwent physical examination and quantitative magnetic resonance imaging of the trapezius muscles. A T2‐prepared turbo spin-echo sequence was acquired for manual segmentation of the trapezius muscles and extraction of mean T2 values.

Results

There were no statistically significant differences regarding age, sex, body mass index, or number of myofascial trigger points (mTrPs) between groups. All patients with migraine presented with mTrPs in the trapezius muscles. T2 of the entire trapezius muscles was significantly higher in the migraine group when compared to controls (31.1 ± 0.8 ms vs. 30.1 ± 1.1 ms; p = 0.002).

Conclusions

Elevated T2 values of the trapezius muscles may indicate subtle inflammatory processes within musculature among patients with migraine because T2 increase is likely to stem from edematous changes. Future work may validate this finding in larger cohorts, but muscle T2 might have potential to develop into a viable in vivo biomarker for muscular affection in migraine.

The pathophysiological nature of sarcomeres in trigger points in patients with myofascial pain syndrome: A preliminary study

BACKGROUND

Myofascial pain syndrome (MPS) has a high global prevalence and is associated with myofascial trigger points (MTrPs) in taut bands or nodules. Little is known about the aetiology. The current study assessed the pathophysiological characteristics of MTrPs in MPS patients.

METHODS

Biopsies of the trapezius muscle were collected from the MTrPs of MPS patients (MTrP group; n = 29) and from healthy controls (control group; n = 24), and their morphologies were analysed via haematoxylin-eosin (H&E) and Masson staining. A protein microarray was used to detect the receptor tyrosine kinase (RTK) family proteins. mRNA and long non-coding RNA (lncRNA) sequencing and analysis were conducted, and immunohistochemistry and Western blotting were used to examine the expression of EphB and Rho family proteins.

RESULTS

Abnormally contracted sarcomeres showed enlarged, round fibres without inflammation or fibrosis. An lncRNA-mRNA network analysis revealed activation of muscle contraction signalling pathways in MTrP regions. Among RTK family proteins, 15 exhibited increased phosphorylation, and two exhibited decreased phosphorylation in the MTrP regions relative to control levels. In particular, EphB1/EphB2 phosphorylation was increased on the muscle cell membranes of abnormal sarcomeres. RhoA and Rac1, but not cell division control protein 42 (Cdc42), were activated in the abnormal sarcomeres.

CONCLUSIONS

EphB1/EphB2 and RhoA/Rac1 might play roles in the aetiology of abnormally contracted sarcomeres in MTrPs without inflammatory cell infiltration and fibrotic adhesion.

SIGNIFICANCE

Contracted sarcomeres were found in MTrP regions, which is consistent with the MTrP formation hypothesis. EphB1/EphB2 and RhoA/Rac1 might play roles in the sarcomere contractile sites of MTrPs, which may be promising therapeutic targets.

Evidence of Mitochondrial Dysfunction in Fibromyalgia: Deviating Muscle Energy Metabolism Detected Using Microdialysis and Magnetic Resonance

In fibromyalgia (FM) muscle metabolism, studies are sparse and conflicting associations have been found between muscle metabolism and pain aspects. This study compared alterations in metabolic substances and blood flow in erector spinae and trapezius of FM patients and healthy controls. FM patients (n = 33) and healthy controls (n = 31) underwent a clinical examination that included pressure pain thresholds and physical tests, completion of a health questionnaire, participation in microdialysis investigations of the etrapezius and erector spinae muscles, and also underwent phosphorus-31 magnetic resonance spectroscopy of the erector spinae muscle. At the baseline, FM had significantly higher levels of pyruvate in both muscles. Significantly lower concentrations of phosphocreatine (PCr) and nucleotide triphosphate (mainly adenosine triphosphate) in erector spinae were found in FM. Blood flow in erector spinae was significantly lower in FM. Significant associations between metabolic variables and pain aspects (pain intensity and pressure pain threshold PPT) were found in FM. Our results suggest that FM has mitochondrial dysfunction, although it is unclear whether inactivity, obesity, aging, and pain are causes of, the results of, or coincidental to the mitochondrial dysfunction. The significant regressions of pain intensity and PPT in FM agree with other studies reporting associations between peripheral biological factors and pain aspects.

Effects of a workplace exercise program on physical capacity and lower back symptoms in hospital nursing assistants: a randomized controlled trial

PURPOSE

Considering the relevance of muscle strength for sustaining good musculoskeletal health among workers who perform physically demanding work, the aim of this study was to evaluate the effectiveness of a therapeutic exercise program on muscle strength and low back symptoms among hospital nursing assistants.

METHODS

One hundred and twenty-nine nursing assistants filled out a questionnaire on personal, occupational information and health status, which allowed the identification of workers able to exercise. Ninety participants were randomly allocated to an intervention and a reference group. The therapeutic exercise program (TEP) lasted 12 weeks and included warm-up, strengthening and stretching exercises. Muscle strength of trunk flexors and trunk extensors, hamstring flexibility, and low back symptoms were evaluated before and after the intervention period by two blinded assessors. The comparison between groups was carried out using Mann-Whitney and χ² tests at a significance level of 0.05.

RESULTS

The average participation in the exercise program was 17.5 sessions. Results showed increased trunk flexors muscle strength (p = 0.002; effect size: 0.77), improved pressure pain threshold for dorsal longissimus (p = 0.001; effect size > 0.8), and reduced low back symptoms (p = 0.002; OR = 6.25). No differences between groups were identified for back extensor muscle strength or flexibility.

CONCLUSION

The exercise program applied is a feasible intervention which resulted clinically relevant results for nursing assistants' musculoskeletal health expressed through trunk flexors muscle strength improvement and low back symptoms control among nursing assistants. This RCT brings contribution to the Occupational Health field as the exercise program applied resulted in clinically relevant results for nursing assistants' musculoskeletal health. This study brings contribution especially for low-income and middle-income countries where low back pain and disability can be considered more severe as adequate resources to address the problem are scarce. Thus, we must highlight the importance of low-cost preventive strategies, like exercise programs carried out in hospital settings to avoid the progress of disability among active nursing personnel.

Effects of 4-Week Diacutaneous Fibrolysis on Myalgia, Mouth Opening, and Level of Functional Severity in Women With Temporomandibular Disorders: A Randomized Controlled Trial

OBJECTIVE

The purpose of this study was to assess the effects of 4-week protocol of diacutaneous fibrolysis (DF) compared with simulated DF (sham-DF) on myalgia and mouth opening.

METHODS

In a sham randomized controlled trial, 34 women with temporomandibular disorders and myofascial pain were randomly divided as intervention group (IG) and sham-DF group (SG). The IG received 4 weeks of real DF, and the SG received sham. Pain was assessed through the visual analog scale and pressure pain thresholds (PPTs) on the temporomandibular joint (TMJ), and over the temporal and masseter muscles. The Mandibular Function Impairment Questionnaire was used to classify the participants regarding to the severity of the functional limitation related to TMD.

RESULTS

Pain scores decreased for both groups, but the IG showed lower values at week 4, with between-group differences. Bilateral temporal PPT showed higher values at week 4, with between-group differences. The SG had lower PPTs but the IG had higher PPTs, both compared to baseline results. The time-by-group interaction and the frequency of participants above 40 mm of mouth opening showed a significant difference for the IG over time with higher results at the 4-week assessment compared to its own baseline. Both groups showed lower MFIQ scores from baseline to 4-week assessment. There was a lower frequency of a moderate level of severity for the IG. No differences were observed for TMJ or for the masseter muscles PPT.

CONCLUSION

Improvements were observed for visual analog scale scores and PPTs on temporal muscles. There was a group-by-time interaction in the IG, suggesting a possible potential use of DF for mouth opening.

Daytime changes of salivary biomarkers involved in pain

The study aimed to investigate salivary levels of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), substance P (SP) and glutamate at five time points from morning to afternoon in a well-characterised healthy and pain-free individuals. Ten young adults were included. Unstimulated and stimulated whole saliva were collected from each participant repeatedly across the day. Blood samples were drawn in connection with the first and last saliva sample as reference standard. Levels of NGF and BDNF were determined using gel-free Western blot technology, glutamate levels were analysed using a colorimetric assay, and SP was determined using a commercially available ELISA. Salivary NGF and BDNF showed significant differences between the different collection times in both unstimulated (NGF; P = .006; BDNF; P = .026) and stimulated whole saliva (NGF; P = .006; BDNF; P = .019). The highest concentrations of the neuropeptides were expressed in the early morning, and they thereafter decreased across the day. In contrast, the expression of salivary glutamate and SP did not show any significant changes across the day. Plasma levels of NGF were higher in the evening sample (P = .028); otherwise, there were no significant differences for any of the other markers between morning and evening samples. NGF and BDNF in whole saliva showed a significant variation across the day. On the contrary, no variation in the levels of SP and glutamate was detected. These findings highlight the importance of consistency in the collection time and approach in biomarker studies using saliva.

The impact of statins on physical activity and exercise capacity: an overview of the evidence, mechanisms, and recommendations

PURPOSE

Statins are among the most widely prescribed medications worldwide. Considered the 'gold-standard' treatment for cardiovascular disease (CVD), statins inhibit HMG-CoA reductase to ultimately reduce serum LDL-cholesterol levels. Unfortunately, the main adverse event of statin use is the development of muscle-associated problems, referred to as SAMS (statin-associated muscle symptoms). While regular moderate physical activity also decreases CVD risk, there is apprehension that physical activity may induce and/or exacerbate SAMS. While much work has gone into identifying the epidemiology of SAMS, only recent research has focused on the extent to which these muscle symptoms are accompanied by functional declines. The purpose of this review is to provide an overview of possible mechanisms underlying SAMS and summarize current evidence regarding the relationship between statin treatment, physical activity, exercise capacity, and SAMS development.

METHODS

PubMed and Google Scholar databases were used to search the most relevant and up-to-date peer-reviewed research on the topic.

RESULTS

The mechanism(s) behind SAMS, including altered mitochondrial metabolism, reduced coenzyme Q10 levels, reduced vitamin D levels, impaired calcium homeostasis, elevated extracellular glutamate, and genetic polymorphisms, still lack consensus and remain up for debate. Our summation of the evidence leads us to suggest that the etiology of SAMS development is likely multifactorial. Our review also demonstrates that there is limited evidence for statins impairing exercise adaptations or reducing exercise capacity for the majority of the investigated populations.

CONCLUSION

The available evidence indicates that the benefits of engaging in physical activity while on statin medication largely outweigh the risks.

Improving characterization and diagnosis quality of myofascial pain syndrome: a systematic review of the clinical and biomarker overlap with delayed onset muscle soreness

INTRODUCTION

Myofascial pain syndrome (MPS) is one of the most common conditions of chronic musculoskeletal pain, yet its mechanisms are still poorly understood. Delayed Onset Muscle Soreness (DOMS) is also a regional pain syndrome that has clinical similarities to MPS, but has been better investigated. Emerging research suggests that DOMS may be a valid experimental model for studying MPS; however, a comparison of the similarities and differences of these two conditions has previously not been performed. Herein, we aimed to identify the similarities and differences in the clinical features and biomarkers between DOMS and MPS in order to better define MPS and identify future areas of (DOMS-informed) MPS research.

EVIDENCE ACQUISITION

In order to identify similarities and differences in the clinical manifestation and biomarkers of DOMS and MPS, scoping literature searches were performed using Medline (1965-2019), Embase (1966-2019) and Central (1966-2019) databases. Fifty-three full-text articles were reviewed out of the 2836 articles retrieved in the search.

EVIDENCE SYNTHESIS

A scoping review of the literature demonstrated that DOMS and MPS similarly present as conditions of musculoskeletal pain that are associated with decreased strength and limited range of motion. However, while taut bands and discrete tender spots were described in DOMS, none of the studies reviewed have characterized whether these tender points represent the classic myofascial trigger point phenomenon observed in MPS. Certain systemic circulation biomarkers, including inflammatory cytokines and growth factors, were commonly elevated in MPS and DOMS; further research is needed to determine if other biomarkers that are currently characterized in DOMS are useful to enhance the clinical evaluation of MPS.

CONCLUSIONS

DOMS and MPS share clinical and biomarker similarities suggesting that DOMS may be a useful model for studying MPS.

Glutamate sensing in biofluids: recent advances and research challenges of electrochemical sensors

Electrochemical sensing guidelines for glutamate in biofluids, associated with different diseases, providing knowledge translation among science, engineering, and medical professionals.

Calcium Fluxes in Work-Related Muscle Disorder: Implications from a Rat Model

Introduction

Ca²⁺ regulatory excitation-contraction coupling properties are key topics of interest in the development of work-related muscle myalgia and may constitute an underlying cause of muscle pain and loss of force generating capacity.

Method

A well-established rat model of high repetition high force (HRHF) work was used to investigate if such exposure leads to an increase in cytosolic Ca²⁺ concentration ([Ca²⁺]_i) and changes in sarcoplasmic reticulum (SR) vesicle Ca²⁺ uptake and release rates.

Result

Six weeks exposure of rats to HRHF increased indicators of fatigue, pain behaviors, and [Ca²⁺]_i, the latter implied by around 50-100% increases in pCam, as well as in the Ca²⁺ handling proteins RyR1 and Casq1 accompanied by an ∼10% increased SR Ca²⁺ uptake rate in extensor and flexor muscles compared to those of control rats. This demonstrated a work-related altered myocellular Ca²⁺ regulation, SR Ca²⁺ handling, and SR protein expression.

Discussion

These disturbances may mirror intracellular changes in early stages of human work-related myalgic muscle. Increased uptake of Ca²⁺ into the SR may reflect an early adaptation to avoid a sustained detrimental increase in [Ca²⁺]_i similar to the previous findings of deteriorated Ca²⁺ regulation and impaired function in fatigued human muscle.

Discomfort glare and psychological stress during computer work: subjective responses and associations between neck pain and trapezius muscle blood flow

PURPOSE

Exposure to additional environmental stress during computer work, such as visual and psychological demands, is associated with increased eye and neck discomfort, altered moods, and reduced well-being. The aim of this study is to elucidate further how subjective responses in healthy, young females with normal binocular vision are affected by glare and psychological stress during computer work, and to investigate possible associations between trapezius muscle blood flow and neck pain development.

METHODS

43 females participated in a laboratory experiment with a within-subject design. Four 10-min computer work conditions with exposure to different stressors were performed at an ergonomically optimal workstation, under the following series of conditions: no additional stress, visual stress (induced as direct glare from a large glare source), psychological stress, and combined visual and psychological stress. Before and immediately after each computer work condition, questionnaires regarding different visual and eye symptoms, neck and shoulder symptoms, positive and negative state moods, perceived task difficulty, and perceived ambient lighting were completed. Associations between neck pain and trapezius muscle blood flow were also investigated.

RESULTS

Exposure to direct glare induced greater development of visual/eye symptoms and discomfort, while psychological stress exposure made participants feel more negative and stressed. The perception of work lighting during glare exposure was closely related to perceived stress, and associations between visual discomfort and eyestrain, and neck pain were observed in all conditions. Furthermore, participants with high trapezius muscle blood flow overall reported more neck pain, independent of exposure.

CONCLUSIONS

Exposure to visual and psychological stresses during computer work affects the development of symptoms and negative moods in healthy, young females with normal binocular vision, but in different ways. The results also demonstrate the complex interactions involved in symptom development and lighting appraisal during computer work. When optimizing computer workstations, the complexity of the field must be taken into account, and several factors, including visual conditions, must be considered carefully.

Ovarian Hormone-dependent and Spinal ERK Activation-regulated Nociceptive Hypersensitivity in Female Rats with Acid Injection-induced Chronic Widespread Muscle Pain

Symptoms of chronic widespread muscle pain (CWP) meet most of the diagnostic criteria for fibromyalgia syndrome, which is prevalent in females. We used an acid injection-induced muscle pain (AIMP) model to mimic CWP. After female rats received an ovariectomy (OVX), acid saline solution was injected into the left gastrocnemius muscle. Time courses of changes in pain behaviours and p-ERK in the spinal cord were compared between groups. Intrathecal injections of oestradiol (E2) to the OVX group before two acid injections and E2 or progesterone (P4) injections in male rats were compared to evaluate hormone effects. We found that repeated acid injections produced mechanical hypersensitivity and enhanced p-ERK expression in the spinal dorsal horn. OVX rats exhibited significantly less tactile allodynia than did the rats in the other groups. The ERK inhibitor U0126 alleviated mechanical allodynia with lower p-ERK expression in the sham females but did not affect the OVX rats. Intrathecal E2 reversed the attenuated mechanical hypersensitivity in the OVX group, and E2 or P4 induced transient hyperalgesia in male rats. Accordingly, our results suggested that ovarian hormones contribute to AIMP through a spinal p-ERK-mediated pathway. These findings may partially explain the higher prevalence of fibromyalgia in females than males.

The Effect of Microdialysis Catheter Insertion on Glutamate and Serotonin Levels in Masseter Muscle in Patients with Myofascial Temporomandibular Disorders and Healthy Controls

Myofascial temporomandibular disorders (TMD) are the most common cause of chronic pain in the orofacial region. Microdialysis has been used to study metabolic changes in the human masseter muscle. The insertion of the microdialysis probe causes acute tissue trauma that could affect the metabolic milieu and thereby influence the results when comparing healthy subjects to those with TMD. This study aimed to investigate the levels of serotonin and glutamate during the acute tissue trauma period in healthy subjects and in patients with TMD. Microdialysis was carried out in 15 patients with TMD and 15 controls, and samples were collected every 20 min during a period of 140 min. No significant alterations of serotonin or glutamate were observed over the 2 h period for the healthy subjects. For the TMD group, a significant decrease in serotonin was observed over time (p < 0.001), followed by a significant increase between 120 and 140 min (p < 0.001). For glutamate, a significant reduction was observed at 40 min compared to baseline. The results showed that there was a spontaneous increase of serotonin 2 h after the insertion of the catheter in patients with TMD. In conclusion, the results showed that there are differences in the masseter muscle levels of serotonin and glutamate during acute nociception in patients with myofascial TMD compared to healthy subjects.

Saliva as a medium to detect and measure biomarkers related to pain

Saliva is often neglected as a body fluid of diagnostic or prognostic value, even though generally well accepted by the patients. This is due to lack of a standardized collection procedure. The aim of this study was to identify the ideal saliva collection technique and develop new sensitive methods to detect and analyse markers related to pain in healthy pain-free subjects. Plasma and five different saliva collection approached was evaluated during strictly controlled conditions. Levels of nerve growth factor (NGF), calcitonin gene-related peptide (CGRP) and brain derived neurotropic factor (BDNF) were determined using novel western blotting based technology. Glutamate and substance P (SP) was determined using commercial available methods. Several new isoforms were found for NGF, CGRP and BDNF in saliva. The isoform pattern showed significant variation in both expression and chemiluminescence levels between different collection methods. New sensitive methods to study pain related markers in saliva were developed in this study. Furthermore, we are first to demonstrate a correlation between the Glutamate concentration in stimulated whole saliva and blood. However, the fundamental conclusion drawn is the importance of consistency in the collection method.

Investigation of biomarkers alterations after an acute tissue trauma in human trapezius muscle, using microdialysis

Alterations in muscle milieu are suggested as important activity of peripheral drive in patients with chronic musculoskeletal pain (CMP). Microdialysis (MD) has been used in monitoring altered metabolic response pattern in muscles. However, the insertion of MD probe causes a local tissue trauma. Whether and how metabolites in trapezius muscle are affected by acute tissue trauma is unknown. Hence, this study investigated the metabolic response and nociceptive reaction of the tissue following MD probe insertion in patients with CMP and healthy individuals. Fifty-nine patients and forty pain-free volunteers were recruited. Pressure pain thresholds (PPTs) were obtained at the trapezius and tibialis muscles. Pain questionnaires determined the levels of pain related aspects. MD (20 kDa cut-off) was performed in the trapezius and samples were collected within 40 min. Interstitial concentration of the metabolites was analyzed by a two-way-mixed-ANOVA. The metabolic response pattern changed over time and alterations in the level of metabolites could be seen in both CMP and healthy controls. Pain questionnaires and pain intensities manifested clinical aspects of pain closely to what CMP patients describe. Analyzing metabolites due to acute tissue trauma by aid of MD may be a useful model to investigate altered metabolic response effect in CMP.

Systematic review of quantitative imaging biomarkers for neck and shoulder musculoskeletal disorders

Background

This study systematically summarizes quantitative imaging biomarker research in non-traumatic neck and shoulder musculoskeletal disorders (MSDs). There were two research questions: 1) Are there quantitative imaging biomarkers associated with the presence of neck and shoulder MSDs?, 2) Are there quantitative imaging biomarkers associated with the severity of neck and shoulder MSDs?

Methods

PubMed and SCOPUS were used for the literature search. One hundred and twenty-five studies met primary inclusion criteria. Data were extracted from 49 sufficient quality studies.

Results

Most of the 125 studies were cross-sectional and utilized convenience samples of patients as both cases and controls. Only half controlled for potential confounders via exclusion or in the analysis. Approximately one-third reported response rates. In sufficient quality articles, 82% demonstrated at least one statistically significant association between the MSD(s) and biomarker(s) studied. The literature synthesis suggested that neck muscle size may be decreased in neck pain, and trapezius myalgia and neck/shoulder pain may be associated with reduced vascularity in the trapezius and reduced trapezius oxygen saturation at rest and in response to upper extremity tasks. Reduced vascularity in the supraspinatus tendon may also be a feature in rotator cuff tears. Five of eight studies showed an association between a quantitative imaging marker and MSD severity.

Conclusions

Although research on quantitative imaging biomarkers is still in a nascent stage, some MSD biomarkers were identified. There are limitations in the articles examined, including possible selection bias and inattention to potentially confounding factors. Recommendations for future studies are provided.

Electronic supplementary material

The online version of this article (doi:10.1186/s12891-017-1694-y) contains supplementary material, which is available to authorized users.

Physical Activity as Cause and Cure of Muscular Pain: Evidence of Underlying Mechanisms

Work-related physical activity (PA), in terms of peak loads and sustained and/or repetitive contractions, presents risk factors for the development of muscular pain and disorders. However, PA as a training tailored to the employee's work exposure, health, and physical capacity offers prevention and rehabilitation. We suggest the concept of "Intelligent Physical Exercise Training" relying on evidence-based sports science training principles.

Alterations of anti-inflammatory lipids in plasma from women with chronic widespread pain - a case control study

Background

Chronic widespread pain conditions (CWP) such as the pain associated with fibromyalgia syndrome (FMS) are significant health problems with unclear aetiology. Although CWP and FMS can alter both central and peripheral pain mechanisms, there are no validated markers for such alterations. Pro- and anti-inflammatory components of the immune system such as cytokines and endogenous lipid mediators could serve as systemic markers of alterations in chronic pain. Lipid mediators associated with anti-inflammatory qualities – e.g., oleoylethanolamide (OEA), palmitoylethanolamide (PEA), and stearoylethanolamide (SEA) – belong to N-acylethanolamines (NAEs). Previous studies have concluded that these lipid mediators may modulate pain and inflammation via the activation of peroxisome proliferator activating receptors (PPARs) and the activation of PPARs may regulate gene transcriptional factors that control the expression of distinct cytokines.

Methods

This study investigates NAEs and cytokines in 17 women with CWP and 21 healthy controls. Plasma levels of the anti-inflammatory lipids OEA, PEA, and SEA, the pro-inflammatory cytokines TNF-α, IL-1β, IL-6, and IL-8, and the anti-inflammatory cytokine IL-10 were investigated. T-test of independent samples was used for group comparisons. Bivariate correlation analyses, and multivariate regression analysis were performed between lipids, cytokines, and pain intensity of the participants.

Results

Significantly higher levels of OEA and PEA in plasma were found in CWP. No alterations in the levels of cytokines existed and no correlations between levels of lipids and cytokines were found.

Conclusions

We conclude that altered levels of OEA and PEA might indicate the presence of systemic inflammation in CWP. In addition, we believe our findings contribute to the understanding of the biochemical mechanisms involved in chronic musculoskeletal pain.

Self-administered physical exercise training as treatment of neck and shoulder pain among military helicopter pilots and crew: a randomized controlled trial

Background

Neck pain is frequent among military helicopter pilots and crew-members, and pain may influence individual health and work performance. The aim of this study was to examine if an exercise intervention could reduce neck pain among helicopter pilots and crew-members.

Methods

Thirty-one pilots and thirty-eight crew-members were randomized to either an exercise-training-group (n = 35) or a reference-group (n = 34). The exercise-training-group received 20-weeks of specific neck/shoulder training. The reference-group received no training. Primary outcome: Intensity of neck pain previous 3-months (scale 0-10). Secondary outcomes: additional neck/shoulder pain intensity variables and pressure-pain-threshold in the trapezius muscle (TRA) and upper-neck-extensor muscles (UNE). Regular training adherence was defined as ≥1 training session a week. Statistical analyses performed were intention-to-treat and per-protocol. Students t-test was performed (p < 0.05).

Results

Intensity of neck pain previous 3-months at baseline was: 2.2 ± 1.8 and previous 7-days: 1.0 ± 1.5, and pressure-pain-threshold in TRA and UNE (right/left) was in kPa: 424 ± 187 / 434 ± 188 and 345 ± 157 / 371 ± 170 in the exercise-training-group, and 416 ± 177 / 405 ± 163 and 334 ± 147 / 335 ± 163 in the reference-group, with no differences between groups. Intention-to-treat-analysis revealed no significant between-group-differences in neck pain intensity and pressure-pain-threshold. Between-group-differences, including participants who trained regularly (n = 10) were also non-significant. Within-group-changes were significant among participants with regular training adherence in the exercise-training-group regarding intensity of neck pain previous 3-months (from 2.2 ± 0.6 to 1.3 ± 1.3, p = 0.019). Likewise, within the whole exercise-training-group, neck pain previous 7-days decreased (from 1.0 ± 1.4 to 0.6 ± 1.1, p = 0.024). Additional within-group-changes regarding pressure-pain-threshold in kPa were for the reference-group a reduction in TRA and UNE (right/left) to: 342 ± 143 / 332 ± 154 and 295 ± 116 / 292 ± 121 implying increased pain sensitivity, while for the exercise-training-group only a reduction in left TRA was seen: 311 ± 113.

Conclusions

The exercise intervention did not reduce neck pain among helicopter pilots and crew-members as no significant between-group-differences were found. However, some trends were demonstrated as some neck pain intensity and sensitivity improved more within the exercise-training-group but not within the reference-group. The lack of effect may be due to low adherence since only ~ 1/3 of subjects in the exercise-training-group engaged in regular training which may be due to the self-administration of the training.

Trial registrations

Ethical committee of Southern Denmark (S-20120121) 29 August, 2012. Clinical Trail Registration (NCT01926262) 16 August, 2013.

Clear differences in cerebrospinal fluid proteome between women with chronic widespread pain and healthy women - a multivariate explorative cross-sectional study

Introduction

Frequent chronic local pain can develop into chronic widespread pain (CWP). The spread of pain is correlated with pain intensity, anxiety, and depression, conditions that ultimately lead to a poor quality of life. Knowledge is incomplete about CWP’s etiology, although it has been suggested that both central hyperexcitability and/or a combination with peripheral factors may be involved. Cerebrospinal fluid (CSF) could act as a mirror for the central nervous system as proteins are signal substances that activate the formation of algesics and control nociceptive processes. To this end, this study investigates the CSF protein expression in women with CWP and in female healthy controls.

Materials and methods

This study included 12 female patients with CWP diagnosed according to the American College of Rheumatology criteria with 13 healthy age- and sex-matched pain-free subjects. All subjects went through a clinical examination and answered a health questionnaire that registered sociodemographic and anthropometric data, pain characteristics, psychological status, and quality of life rating. CSF was collected by lumbar puncture from each subject. Two-dimensional gel electrophoresis in combination with mass spectrometry was used to analyze the CSF proteome. This study identifies proteins that significantly discriminate between the two groups using multivariate data analysis (MVDA) (i.e., orthogonal partial least squares discriminant analysis [OPLS-DA]).

Results

There were no clinically significant levels of psychological distress and catastrophization presented in subjects with CWP. MVDA revealed a highly significant OPLS-DA model where 48 proteins from CSF explained 91% (R²) of the variation and with a prediction of 90% (Q²). The highest discriminating proteins were metabolic, transport, stress, and inflammatory.

Conclusion

The highest discriminating proteins (11 proteins), according to the literature, are involved in apoptotic regulations, anti-inflammatory and anti-oxidative processes, the immune system, and endogenous repair. The results of this explorative study may indicate the presence of neuro-inflammation in the central nervous system of CWP patients. Future studies should be larger and control for confounders and determine which alterations are unspecific/general and which are specific changes.

Signs of ongoing inflammation in female patients with chronic widespread pain: A multivariate, explorative, cross-sectional study of blood samples

This cross-sectional study investigates the plasma inflammatory profile of chronic widespread pain (CWP) patients compared to healthy controls (CON). Rather than analyzing a relatively few substances at a time, we used a new multiplex proximity extension assay (PEA) panel that enabled the simultaneous analysis of 92 inflammation-related proteins, mainly cytokines and chemokines.Seventeen women with CWP and 21 female CON participated and a venous blood sample was drawn from all subjects. Pain intensity and pain thresholds for pressure, heat, and cold were registered. A PEA panel (92 proteins) was used to analyze the blood samples. Multivariate data analysis by projection was used in the statistical analyses.Eleven proteins significantly differentiated the CON and CWP subjects (R = 0.58, Q = 0.37, analysis of variance of cross-validated predictive residuals P = 0.006). It was not possible to significantly regress pain thresholds within each group (CON or CWP). Positive significant correlations existed between several proteins and pain intensities in CWP, but the model reliability of the regression was poor.CWP was associated with systemic low-grade inflammation. Larger studies are needed to confirm the results and to investigate which alterations are condition-specific and which are common across chronic pain conditions. The presence of inflammation could promote the spreading of pain, a hallmark sign of CWP. As it has been suggested that prevalent comorbidities to pain (e.g., depression and anxiety, poor sleep, and tiredness) also are associated with inflammation, it will be important to determine whether inflammation may be a common mediator.

Increased levels of intramuscular cytokines in patients with jaw muscle pain

BACKGROUND

The aim of this study was to investigate cytokine levels in the masseter muscle, their response to experimental tooth-clenching and their relation to pain, fatigue and psychological distress in patients with temporomandibular disorders (TMD) myalgia.

METHODS

Forty women, 20 with TMD myalgia (Diagnostic Criteria for TMD) and 20 age-matched healthy controls participated. Intramuscular microdialysis was performed to sample masseter muscle cytokines. After 140 min (baseline), a 20-minute tooth-clenching task was performed (50% of maximal voluntary contraction force). Pain (Numeric rating scale 0-10) and fatigue (Borg's Ratings of Perceived Exertion 6-20) were assessed throughout microdialysis, while pressure-pain thresholds (PPT) were assessed before and after microdialysis. Perceived stress (PSS-10) and Trait Anxiety (STAI) were assessed before microdialysis.

RESULTS

The levels of IL-6, IL-7, IL-8 and IL-13 were higher in patients than controls (Mann Whitney U-test; P's < 0.05) during the entire microdialysis. IL-6, IL-8 and IL-13 changed during microdialysis in both groups (Friedman; P's < 0.05), while IL-1β, IL-7 and GM-CSF changed only in patients (P's < 0.01). IL-6 and IL-8 increased in response to tooth-clenching in both groups (Wilcoxon test; P's < 0.05), while IL-7, IL-13 and TNF increased only in patients (P's < 0.05). Patients had higher pain and fatigue than controls before and after tooth-clenching (P < 0.001), and lower PPTs before and after microdialysis (P < 0.05). There were no correlations between cytokine levels, pain or fatigue. Also, there were no differences in stress or anxiety levels between groups.

CONCLUSIONS

In conclusion, the masseter levels of IL-6, IL-7, IL-8 and IL-13 were elevated in patients with TMD myalgia and increased in response to tooth-clenching. Tooth-clenching increased jaw muscle pain and fatigue, but without correlations to cytokine levels. This implies that subclinical muscle inflammation may be involved in TMD myalgia pathophysiology, but that there is no direct cause-relation between inflammation and pain.

Beneficial Effects of Dry Needling for Treatment of Chronic Myofascial Pain Persist for 6 Weeks After Treatment Completion

BACKGROUND

Dry needling is an effective treatment for reducing pain associated with active myofascial trigger points (a-MTrPs) in the short term. The duration of the benefits of this treatment have not been fully assessed.

OBJECTIVE

To determine whether the benefits of dry needling (DN) of a-MTrPs are sustained 6 weeks posttreatment.

DESIGN

Follow-up of a prospective study.

SETTING

University.

PARTICIPANTS

A total of 45 patients (13 male and 32 female) with cervical pain >3 months and a-MTrPs in the upper trapezius who completed 3 DN treatments and who were evaluated 6 weeks posttreatment.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

Primary outcomes were changes from baseline to follow-up in scores for the verbal analogue scale (VAS), Brief Pain Inventory (BPI), and MTrP status. MTrPs were rated as active (spontaneously painful), latent (painful only on compression), and nonpalpable nodule. Responders were patients whose MTrP status changed from active to latent or nonpalpable nodule (resolved). Secondary outcomes were pain pressure threshold (PPT), Profile of Mood States, Oswestry Disability Index (ODI), MOS 36-Item Short-Form Health Survey (SF-36), and cervical range of motion.

RESULTS

Pain measures remained significantly improved 6 weeks posttreatment (P < .003), as did the SF-36 physical functioning score (0.01) and ODI (P = .002). Side bending and PPT for subjects with unilateral MTrPs had sustained improvement (P = .002). The number of subjects with sustained MTrP response at 6 weeks was significant (P < .001). Comparing responders to nonresponders, the changes in VAS and BPI were statistically significant (P = .006, P = .03) but the change in PPT was not. Patients with higher baseline VAS scores had a higher risk of not responding to DN; those with a greater drop in VAS score from baseline had a higher probability of sustained response. A 1-unit decrease in VAS at baseline resulted in a 6.3-fold increase in the odds of being a responder versus a nonresponder (P = .008).

CONCLUSIONS

In this study, there was sustained reduction of pain scores after completion of DN, which is more likely with a greater drop in VAS score. Patients with higher baseline VAS scores are less likely to respond to DN. Early intervention toward significant pain reduction is likely to be associated with sustained clinical response.

LEVEL OF EVIDENCE

IV.

Influence of Polymorphisms in the HTR3A and HTR3B Genes on Experimental Pain and the Effect of the 5-HT3 Antagonist Granisetron

The aim of this study was to investigate experimentally if 5-HT₃ single nucleotide polymorphisms (SNP) contribute to pain perception and efficacy of the 5-HT₃-antagonist granisetron and sex differences. Sixty healthy participants were genotyped regarding HTR3A (rs1062613) and HTR3B (rs1176744). First, pain was induced by bilateral hypertonic saline injections (HS, 5.5%, 0.2 mL) into the masseter muscles. Thirty min later the masseter muscle on one side was pretreated with 0.5 mL granisetron (1 mg/mL) and on the other side with 0.5 mL placebo (isotonic saline) followed by another HS injection (0.2 mL). Pain intensity, pain duration, pain area and pressure pain thresholds (PPTs) were assessed after each injection. HS evoked moderate pain, with higher intensity in the women (P = 0.023), but had no effect on PPTs. None of the SNPs influenced any pain variable in general, but compared to men, the pain area was larger in women carrying the C/C (HTR3A) (P = 0.015) and pain intensity higher in women with the A/C alleles (HTR3B) (P = 0.019). Pre-treatment with granisetron reduced pain intensity, duration and area to a lesser degree in women (P < 0.05), but the SNPs did not in general influence the efficacy of granisetron. Women carrying the C/T & T/T (HTR3A) genotype had less reduction of pain intensity (P = 0.041) and area (P = 0.005), and women with the C/C genotype (HTR3B) had less reduction of pain intensity (P = 0.030), duration (P = 0.030) and area compared to men (P = 0.017). In conclusion, SNPs did not influence experimental muscle pain or the effect of granisetron on pain variables in general, but there were some sex differences in pain variables that seem to be influenced by genotypes. However, due to the small sample size further research is needed before any firm conclusions can be drawn.

Background, design and conceptual model of the cluster randomized multiple-component workplace study: FRamed Intervention to Decrease Occupational Muscle pain - "FRIDOM"

Background

Several RCT studies have aimed to reduce either musculoskeletal disorders, sickness presenteeism, sickness absenteeism or a combination of these among females with high physical work demands. These studies have provided evidence that workplace health promotion (WHP) interventions are effective, but long-term effects are still uncertain. These studies either lack to succeed in maintaining intervention effects or lack to document if effects are maintained past a one-year period. This paper describes the background, design and conceptual model of the FRIDOM (FRamed Intervention to Decrease Occupational Muscle pain) WHP program among health care workers. A job group characterized by having high physical work demands, musculoskeletal disorders, high sickness presenteeism - and absenteeism.

Methods

FRIDOM aimed to reduce neck and shoulder pain. Secondary aims were to decrease sickness presenteeism, sickness absenteeism and lifestyle-diseases such as other musculoskeletal disorders as well as metabolic-, and cardiovascular disorders – and to maintain participation to regular physical exercise training, after a one year intervention period. The entire concept was tailored to a population of female health care workers. This was done through a multi-component intervention including 1) intelligent physical exercise training (IPET), dietary advice and weight loss (DAW) and cognitive behavioural training (CBT).

Discussion

The FRIDOM program has the potential to provide evidence-based knowledge of the pain reducing effect of a multi component WHP among a female group of employees with a high prevalence of musculoskeletal disorders and in a long term perspective evaluate the effects on sickness presenteeism and absenteeism as well as risk of life-style diseases.

Trial registration

NCT02843269, 06.27.2016 - retrospectively registered.

Electronic supplementary material

The online version of this article (doi:10.1186/s12889-016-3758-6) contains supplementary material, which is available to authorized users.

High levels of endogenous lipid mediators (N-acylethanolamines) in women with chronic widespread pain during acute tissue trauma

Although chronic widespread musculoskeletal pain is a significant health problem, the molecular mechanisms involved in developing and maintaining chronic widespread musculoskeletal pain are poorly understood. Central sensitization mechanisms maintained by stimuli from peripheral tissues such as muscle have been suggested. Lipid mediators with anti-inflammatory characteristics such as endogenous ligands of peroxisome proliferator activating receptor-α, oleoylethanolamide, and palmitoylethanolamide are suggested to regulate nociceptive transmission from peripheral locations on route towards the central nervous system. This case–control study investigates the levels of anti-inflammatory lipids in microdialysis samples collected during the first 2 h after microdialysis probe insertion and explores the association of these lipids with different pain characteristics in women with chronic widespread musculoskeletal pain (n = 17) and female healthy controls (n = 19). The levels of oleoylethanolamide, palmitoylethanolamide, and stearoylethanolamide were determined. During sampling of dialysate, pain ratings were conducted using a numeric rating scale. Pain thresholds were registered from upper and lower parts of the body. Oleoylethanolamide and stearoylethanolamide levels were significantly higher (p ≤ 0.05) in chronic widespread musculoskeletal pain at all time points. Numeric rating scale correlated with levels of stearoylethanolamide in chronic widespread musculoskeletal pain. Higher levels of lipid mediators could reflect an altered tissue reactivity in response to microdialysis probe insertion in chronic widespread musculoskeletal pain.

Dopamine in plasma - a biomarker for myofascial TMD pain?

Background

Dopaminergic pathways could be involved in the pathophysiology of myofascial temporomandibular disorders (M-TMD). This study investigated plasma levels of dopamine and serotonin (5-HT) in patients with M-TMD and in healthy subjects.

Methods

Fifteen patients with M-TMD and 15 age- and sex-matched healthy subjects participated. The patients had received an M-TMD diagnosis according to the Research Diagnostic Criteria for TMD. Perceived mental stress, pain intensity (0–100-mm visual analogue scale), and pressure pain thresholds (PPT, kPa) over the masseter muscles were assessed; a venous blood sample was taken.

Results

Dopamine in plasma differed significantly between patients with M-TMD (4.98 ± 2.55 nM) and healthy controls (2.73 ± 1.24 nM; P < 0.01). No significant difference in plasma 5-HT was observed between the groups (P = 0.75). Patients reported significantly higher pain intensities (P < 0.001) and had lower PPTs (P < 0.01) compared with the healthy controls. Importantly, dopamine in plasma correlated significantly with present pain intensity (r = 0.53, n = 14, P < 0.05) and perceived mental stress (r = 0.34, n = 28, P < 0.05).

Conclusions

The results suggest that peripheral dopamine might be involved in modulating peripheral pain. This finding, in addition to reports in other studies, suggests that dopaminergic pathways could be implicated in the pathophysiology of M-TMD but also in other chronic pain conditions. More research is warranted to elucidate the role of peripheral dopamine in the pathophysiology of chronic pain.

Specific proteins of the trapezius muscle correlate with pain intensity and sensitivity - an explorative multivariate proteomic study of the trapezius muscle in women with chronic widespread pain

Chronic widespread pain (CWP) including fibromyalgia syndrome (FMS) has a high prevalence and is associated with prominent negative consequences. CWP/FMS exhibits morphological and functional alterations in the central nervous system. The importance of peripheral factors for maintaining the central alterations are under debate. In this study, the proteins from biopsies of the trapezius muscle from 18 female CWP/FMS patients and 19 healthy female controls were analyzed. Pain intensity and pressure pain thresholds (PPT) over the trapezius muscles were registered. Twelve proteins representing five different groups of proteins were important regressors of pain intensity in CWP/FMS (R²=0.99; P<0.001). In the regression of PPT in CWP/FMS, it was found that 16 proteins representing six groups of proteins were significant regressors (R²=0.95, P<0.05). Many of the important proteins were stress and inflammation proteins, enzymes involved in metabolic pathways, and proteins associated with muscle damage, myopathies, and muscle recovery. The altered expression of these proteins may reflect both direct and indirect nociceptive/inflammatory processes as well as secondary changes. The relative importance of the identified proteins and central alterations in CWP need to be investigated in future research. Data from this and the previous study concerning the same cohorts give support to the suggestion that peripheral factors are of importance for maintaining pain aspects in CWP/FMS.

Physiological Evaluation of Childcare-Associated Muscle Load on the Neck and Shoulder Region in Japanese Women

The awkward movements and postures associated with childcare activities can lead to musculoskeletal symptoms in the neck and shoulders. “Dakko” is a method for carrying a child in Japan, and recently it has been reported to cause shoulder stiffness. To our knowledge, the relationship between childcare activities and the physical load on the neck and shoulders is poorly understood. The present study aims to clarify the muscle load on the neck and shoulder region through dakko simulations. First, the association between dakko movements and trapezius muscle activity is clarified by image and electromyogram analyses. Based on this clarification, the distributions and intensity of the muscle load from repetitive dakko movements are clarified using myogenic potential topography. During dakko movements, trapezius muscle activity was observed when lifting up and setting down the child, but not when holding the child. For the repetitive movements, myogenic electrical potentials were observed in the trapezius region after movement load, and individual characteristics of participants were revealed in both the load distributions and the recovery process. Repetitive dakko movements likely induced sustained muscle tonus in the trapezius, which may be a factor related to shoulder stiffness.

Comparison of the Levels of Pro-Inflammatory Cytokines Released in the Vastus Lateralis Muscle of Patients with Fibromyalgia and Healthy Controls during Contractions of the Quadriceps Muscle--A Microdialysis Study

Objective

Fibromyalgia is associated with central hyperexcitability, but it is suggested that peripheral input is important to maintain central hyperexcitability. The primary aim was to investigate the levels of pro-inflammatory cytokines released in the vastus lateralis muscle during repetitive dynamic contractions of the quadriceps muscle in patients with fibromyalgia and healthy controls. Secondarily, to investigate if the levels of pro-inflammatory cytokines were correlated with pain or fatigue during these repetitive dynamic contractions.

Material and Methods

32 women with fibromyalgia and 32 healthy women (controls) participated in a 4 hour microdialysis session, to sample IL-1β, IL-6, IL-8, and TNF from the most painful point of the vastus lateralis muscle before, during and after 20 minutes of repeated dynamic contractions. Pain (visual analogue scale; 0–100) and fatigue Borg’s Rating of Perceived Exertion Scale; 6–20) were assessed before and during the entire microdialysis session.

Results

The repetitive dynamic contractions increased pain in the patients with fibromyalgia (P < .001) and induced fatigue in both groups (P < .001). Perceived fatigue was significantly higher among patients with fibromyalgia than controls (P < .001). The levels of IL-1β did not change during contractions in either group. The levels of TNF did not change during contractions in patients with fibromyalgia, but increased in controls (P < .001) and were significantly higher compared to patients with fibromyalgia (P = .033). The levels of IL-6 and IL-8 increased in both groups alike during and after contractions (P’s < .001). There were no correlations between pain or fatigue and cytokine levels after contractions.

Conclusion

There were no differences between patients with fibromyalgia and controls in release of pro-inflammatory cytokines, and no correlations between levels of pro-inflammatory cytokines and pain or fatigue. Thus, this study indicates that IL-1β, IL-6, IL-8, and TNF do not seem to play an important role in maintenance of muscle pain in fibromyalgia.

Systemic differences in serum metabolome: a cross sectional comparison of women with localised and widespread pain and controls

Chronic musculoskeletal pain exists either as localised to a single region or as widespread to multiple sites in several quadrants of the body. Prospective studies indicate that widespread pain could act as a far end of a continuum of musculoskeletal pain that started with chronic localised pain. The mechanism by which the transition from localised pain to widespread occurs is not clear, although many studies suggest it to be an altered metabolism. In this study, systemic metabolic differences between women with chronic localised neck-shoulder pain (NP), women with chronic widespread pain (CWP) and women who were healthy (CON) were assessed. Blood samples were analysed taking a metabolomics approach using gas chromatography mass spectrometry (GC-MS) and orthogonal partial least square discriminant analysis (OPLS-DA). The metabolomics analysis showed a clear systematic difference in the metabolic profiles between the subjects with NP and the CON but only a weak systematic difference between the subjects with CWP and the CON. This most likely reflects a difference in the portion of the metabolome influenced by the two pain conditions. In the NP group, the overall metabolic profile suggests that processes related to energy utilisation and lipid metabolism could be central aspects of mechanisms maintaining disorder.

Successful aging: Advancing the science of physical independence in older adults

The concept of 'successful aging' has long intrigued the scientific community. Despite this long-standing interest, a consensus definition has proven to be a difficult task, due to the inherent challenge involved in defining such a complex, multi-dimensional phenomenon. The lack of a clear set of defining characteristics for the construct of successful aging has made comparison of findings across studies difficult and has limited advances in aging research. A consensus on markers of successful aging is furthest developed is the domain of physical functioning. For example, walking speed appears to be an excellent surrogate marker of overall health and predicts the maintenance of physical independence, a cornerstone of successful aging. The purpose of the present article is to provide an overview and discussion of specific health conditions, behavioral factors, and biological mechanisms that mark declining mobility and physical function and promising interventions to counter these effects. With life expectancy continuing to increase in the United States and developed countries throughout the world, there is an increasing public health focus on the maintenance of physical independence among all older adults.

Specific exercise training for reducing neck and shoulder pain among military helicopter pilots and crew members: a randomized controlled trial protocol

BACKGROUND

Flight-related neck/shoulder pain is frequent among military helicopter pilots and crew members. With a lifetime prevalence of 81% for pilots and 84% for crew members, the prevalence of neck pain is considered high compared to the general population. The aim of this study was to investigate whether a specifically tailored exercise intervention would reduce the prevalence and incidence rate of neck/shoulder pain among helicopter pilots and crew members.

METHOD

This study used a prospective, parallel group, single blinded, randomized controlled design. Participants were military helicopter pilots and crew members recruited from the Royal Danish Air Force. Inclusion criteria were: 1) employed within the Royal Danish Air Force as a helicopter pilot or onboard crew member (technician, systems-operator, tactical helicopter observer and/or navigator), 2) maintaining operational flight status at enrollment, and 3) operational flying within the previous 6 months. Primary outcome was change in neck and shoulder pain assessed by 1) a modified version of the "Standardized Nordic questionnaire for the analysis of musculoskeletal symptoms" and by 2) pressure pain threshold measurements. Secondary outcomes included: postural balance, strength, stability, and rate of force development for neck and shoulder muscles. Measurements at baseline and follow-up were conducted at four air force bases in Denmark. Sixty-nine participants were individually randomized to either a training group (TG) or a reference group (RG). Participants in the TG performed 20-weeks of physical exercise training divided into sessions of 3 × 20 min per week. Training was completed within working hours and consisted of specific exercise training for the neck and shoulder muscles based on the principles of "Intelligent Physical Exercise Training". The RG received no training.

DISCUSSION

In spite of the high prevalence of flight related neck/shoulder pain among military helicopter pilots and crew members there are currently no evidence based guidelines for the prevention or clinical handling of neck pain among these occupational groups. Results from this study may therefore be beneficial for future establishment of such guidelines.

TRIAL REGISTRATION

Ethical committee of Southern Denmark (S-20120121) 29 August, 2012. Clinical Trail Registration (NCT01926262) 16 August, 2013.

Protein alterations in women with chronic widespread pain--An explorative proteomic study of the trapezius muscle

Chronic widespread pain (CWP) has a high prevalence in the population and is associated with prominent negative individual and societal consequences. There is no clear consensus concerning the etiology behind CWP although alterations in the central processing of nociception maintained by peripheral nociceptive input has been suggested. Here, we use proteomics to study protein changes in trapezius muscle from 18 female patients diagnosed with CWP compared to 19 healthy female subjects. The 2-dimensional gel electrophoresis (2-DE) in combination with multivariate statistical analyses revealed 17 proteins to be differently expressed between the two groups. Proteins were identified by mass spectrometry. Many of the proteins are important enzymes in metabolic pathways like the glycolysis and gluconeogenesis. Other proteins are associated with muscle damage, muscle recovery, stress and inflammation. The altered expressed levels of these proteins suggest abnormalities and metabolic changes in the myalgic trapezius muscle in CWP. Taken together, this study gives further support that peripheral factors may be of importance in maintaining CWP.

Blockade of glutamate release by botulinum neurotoxin type A in humans: a dermal microdialysis study

BACKGROUND

The analgesic action of botulinum neurotoxin type A (BoNTA) has been linked to the blockade of peripheral release of neuropeptides and neurotransmitters in animal models; however, there is no direct evidence of this in humans.

OBJECTIVES

To investigate the effect of BoNTA on glutamate release in humans, using an experimental model of pain and sensitization provoked by capsaicin plus mild heat.

METHODS

Twelve healthy volunteers (six men, six women) were pretreated with BoNTA (10 U) on the volar forearm and with a saline control on the contralateral side. Dermal microdialysis was applied one week later to collect interstitial samples before and after the application of a capsaicin patch (8%) plus mild heat (40°C⁄60 min) to provoke glutamate release, pain and vasodilation. Samples were collected every hour for 3 h using linear microdialysis probes (10 mm, 100 kD). Dialysate was analyzed for glutamate concentration. Pain intensity and skin vasomotor reactions (temperature and blood flow changes) were also recorded.

RESULTS

BoNTA significantly reduced glutamate release compared with saline (P<0.05). The provoked pain intensity was lower in the BoNTA-pretreated arm (P<0.01). The reduction in pain scores was not correlated with glutamate level. Cutaneous blood flow (P<0.05), but not cutaneous temperature (P≥0.05), was significantly reduced by BoNTA. There was a correlation between glutamate level and skin blood flow (r=0.58⁄P<0.05) but not skin temperature (P≥0.05). No differences according to sex were observed in any response.

CONCLUSIONS

The present study provided the first direct evidence supporting the inhibitory effect of BoNTA on glutamate release in human skin, which is potentially responsible for some of the analgesic action of BoNTA.