Foci of Segmentally Contracted Sarcomeres in Trapezius Muscle Biopsy Specimens in Myalgic and Nonmyalgic Human Subjects: Preliminary Results

Stress increases the spontaneous release of ACh and may be involved in the generation and maintenance of myofascial trigger points in mouse

An increase in spontaneous neurotransmission may be related to myofascial pain. Sympathetic neurons innervate most of the neuromuscular junction sand are involved in the modulation of synaptic transmission. Therefore, a direct action of stress on acetylcholine release is expected. For this reason, this study aims to evaluate the relationship between stress and spontaneous neurotransmission. Five acute stressors (immobilization, forced swimming, food and water deprivation, social isolation and ultrasound) were tested in 6 weeks adult Swiss male mice. Subsequently, these types of stress were combined to generate a model of chronic stress. The study of ACh release was evaluated before and after the application of stress by intracellular recording of spontaneous neurotransmission (mEPPs). In each one of the stressors, an increase in the frequency of mEPPs was obtained immediately after treatment, which remained elevated for 5 days and thereafter returned to control values after a week. With chronic stress, a much higher increase in the frequency of mEPPs was obtained and it was maintained for 15 days. In summary, stress, both in its acute and chronic forms, increased spontaneous neurotransmission significantly. There is a possibility that chronic stress is related with the genesis or maintenance of myofascial pain.

A New Unified Theory of Trigger Point Formation: Failure of Pre- and Post-Synaptic Feedback Control Mechanisms

The origin of the myofascial trigger point (TrP), an anomalous locus in muscle, has never been well-described. A new trigger point hypothesis (the new hypothesis) presented here addresses this lack. The new hypothesis is based on the concept that existing myoprotective feedback mechanisms that respond to muscle overactivity, low levels of adenosine triphosphate, (ATP) or a low pH, fail to protect muscle in certain circumstances, such as intense muscle activity, resulting in an abnormal accumulation of intracellular Ca²⁺, persistent actin-myosin cross bridging, and then activation of the nociceptive system, resulting in the formation of a trigger point. The relevant protective feedback mechanisms include pre- and postsynaptic sympathetic nervous system modulation, modulators of acetylcholine release at the neuromuscular junction, and mutations/variants or post-translational functional alterations in either of two ion channelopathies, the ryanodine receptor and the potassium-ATP ion channel, both of which exist in multiple mutation states that up- or downregulate ion channel function. The concepts that are central to the origin of at least some TrPs are the failure of protective feedback mechanisms and/or of certain ion channelopathies that are new concepts in relation to myofascial trigger points.

Myofascial Pain Syndrome: A Nociceptive Condition Comorbid with Neuropathic or Nociplastic Pain

Myofascial pain syndrome is featured by the presence of myofascial trigger points (TrPs). Whether TrPs are primary or secondary phenomena or if they relate to central or peripheral nervous system disorders is controversial. Referred pain, a cardinal sign of TrPs, is a central phenomenon driven by peripheral input. In 2021, the International Association for the Study of Pain (IASP) proposed a clinical criteria and grading system for classifying patients with pain on nociceptive, neuropathic, or nociplastic phenotypes. Myofascial TrP pain has been traditionally categorized as a nociceptive phenotype; however, increasing evidence supports that this condition could be present in patients with predominantly nociplastic pain, particularly when it is associated with an underlying medical condition. The clinical response of some therapeutic approaches for managing TrPs remains unclear. Accordingly, the ability to classify myofascial TrP pain into one of these phenotypes would likely be critical for producing more successful clinical treatment outcomes by a precision medicine approach. This consensus paper presents evidence supporting the possibility of subgrouping individuals with myofascial TrP pain into nociceptive, nociplastic, or mixed-type phenotype. It is concluded that myofascial pain caused by TrPs is primarily a nociceptive pain condition, is unlikely to be classified as neuropathic or nociplastic, but can be present in patients with predominantly neuropathic or nociplastic pain. In the latter cases, management of the predominant central pain problem should be a major treatment goal, but the peripheral drive from TrPs should not be ignored, since TrP treatment has been shown to reduce sensitization-associated symptomatology in nociplastic pain conditions, e.g., fibromyalgia.

Ultrasound Imaging and Guidance for Cervical Myofascial Pain: A Narrative Review

Cervical myofascial pain is a very common clinical condition in the daily practice of musculoskeletal physicians. Physical examination is currently the cornerstone for evaluating the cervical muscles and identifying the eventual presence of myofascial trigger points. Herein, the role of ultrasound assessment in precisely localizing them is progressively mounting in the pertinent literature. Moreover, using ultrasound, not only the muscle tissue but also the fascial and neural elements can be accurately located/evaluated. Indeed, several potential pain generators, in addition to paraspinal muscles, can be involved in the clinical scenario of cervical myofascial pain syndrome. In this article, the authors extensively reviewed the sonographic approach for cervical myofascial pain in order to better diagnose or guide different procedures that can be performed in the clinical practice of musculoskeletal physicians.

From Histoanatomy to Sonography in Myofascial Pain Syndrome: A EURO-MUSCULUS/USPRM Approach

ABSTRACT

Myofascial pain is a common clinical condition, whereby accurate physical examination is usually considered as the cornerstone to identify/diagnose the "trigger point complex," that is, the characteristic finding of this syndrome. Considering the emerging role of ultrasound examination as the natural extension of physical assessment for musculoskeletal disorders, we briefly revise the histological/anatomical features of trigger points and propose a standardized, multistep sonographic approach to myofascial pain. We also imply that the integrated clinical-ultrasound evaluation could be considered as a potential tool to discriminate different phases/subsets of this challenging pathology.

Intramuscular Electrical Stimulation to Trigger Points: Insights into Mechanisms and Clinical Applications—A Scoping Review

Intramuscular electrical stimulation (IMES) is a modality used by clinicians to treat myofascial pain. Recent studies have shown positive results for the use of IMES on pain outcomes, yet studies investigating the potential mechanisms of IMES directly to trigger points (TrPs) are lacking. We performed a scoping review of the literature to summarize the current evidence from human and animal studies on the mechanisms of IMES to the TrP location, and to identify gaps in the existing literature. Electronic literature searches were conducted across five databases from inception to 15 August 2022, including PubMed, Cumulative Index to Nursing and Allied Health Literature (CINAHL), Allied and Complementary Medicine Database (AMED), Scopus and Cochrane Register of Controlled Trials. Four studies met our full criteria for inclusion in this review. Three studies assessed the effects of IMES to TrPs on human subjects with MPS, and only one study used an animal model with experimentally generated TrPs. Based on the results of the included studies, IMES within a TrP region was reported to normalize muscle blood flow, decrease endplate noise of the TrP and elicit antinociceptive effects, at least partially, through engaging supraspinal descending pain inhibitory systems. At present, no clinical implications can be determined on the use of IMES to TrPs due to the limited amount and quality of the available evidence. Further studies investigating the clinical effectiveness and also underlying mechanisms of IMES to TrPs are clearly needed.

Contracture Knots vs. Trigger Points. Comment on Ball et al. Ultrasound Confirmation of the Multiple Loci Hypothesis of the Myofascial Trigger Point and the Diagnostic Importance of Specificity in the Elicitation of the Local Twitch Response. Diagnostics 2022, 12, 321

A recent study published in Diagnostics attempted to visualize trigger points and contracture knots with high-definition ultrasound. Based on their findings, the authors reversed the commonly understood meaning of the two terms. However, they did so without providing any convincing evidence. The authors maintained that their sonography images represented trigger points within contracture knots, supporting the multiple loci hypothesis. On review of the paper, both conclusions seem premature and rather speculative.

Dry Needling Produces Mild Injuries Irrespective to Muscle Stiffness and Tension in Ex Vivo Mice Muscles

Numerous studies have suggested that the myofascial trigger points are responsible for most of the myofascial pain syndrome, so it seems reasonable that its destruction is a good therapeutic solution. The effectiveness of dry needling (DN) has been confirmed in muscles with myofascial trigger points, hypertonicity, and spasticity. The objective of this study is to analyze the need of repetitive punctures on muscles in different situations. The levator auris longus (LAL) muscle and gastrocnemius muscle from adult male Swiss mice were dissected and maintained alive, while being submerged in an oxygenated Ringer’s solution. DN was evaluated under four animal models, mimicking the human condition: normal healthy muscles, muscle fibers with contraction knots, muscles submerged in a depolarizing Ringer solution (KCl-CaCl2), and muscles submerged in Ringer solution with formalin. Thereafter, samples were evaluated with optical microscopy (LAL) and scanning electron microscopy (gastrocnemius). Healthy muscles allowed the penetration of needles between fibers with minimal injuries. In muscles with contraction knots, the needle separated many muscle fibers, and several others were injured, while blood vessels and intramuscular nerves were mostly not injured. Muscles submerged in a depolarizing solution inducing sustained contraction showed more injured muscular fibers and several muscle fibers separated by the needle. Finally, the muscles submerged in Ringer solution with formalin showed a few number of injured muscular fibers and abundant muscle fibers separated by the needle. Scanning electron microscopy images confirm the optical analyses. In summary, dry needling is a technique that causes mild injury irrespective of the muscle tone.

Inhibition of Peripheral ERK Signaling Ameliorates Persistent Muscle Pain Around Trigger Points in Rats

The purpose of this study was to investigate whether the ERK signaling pathway was involved in ameliorating chronic myofascial hyperalgesia from contused gastrocnemius muscle in rats. We established an animal model associated with myofascial pain syndrome and described the mechanism of muscle pain in an animal model. Changes in the mechanical pain threshold were observed 0.5, 1, 2, 3, 4, 5, 8, 12, 18, and 24 h after ERK inhibitor injection around myofascial trigger points (MTrPs) of the gastrocnemius muscle in rats. Morphological changes in gastrocnemius muscle cells were observed by hematoxylin and eosin (H&E) staining. ERK signaling pathway activation was detected through immunohistochemistry and Western blotting. The main morphological characteristics of injured muscle fibers around MTrPs include gathered circular or elliptical shapes of different sizes in the cross-section and continuous inflated and tapering fibers in the longitudinal section. After intramuscular injection of U0126 (ERK inhibitor), the mechanical pain threshold significantly increased. The reduction in mechanical hyperalgesia was accompanied by reduced ERK protein phosphorylation, myosin light chain kinase (MLCK) protein, p-MLC protein expression, and the cross-sectional area of skeletal muscle cells around MTrPs. An ERK inhibitor contributed to the attenuation of mechanical hyperalgesia in the rat myofascial pain model, and the increase in pain threshold may be related to MLCK downregulation and other related contraction-associated proteins by ERK.

Re-Examining Myofascial Pain Syndrome: Toward Biomarker Development and Mechanism-Based Diagnostic Criteria

PURPOSE OF REVIEW

We discuss the need for a mechanism-based diagnostic framework with a focus on the development of objective measures (e.g., biomarkers) that can potentially be added to the diagnostic criteria of the syndrome. Potential biomarkers are discussed in relation to current knowledge on the pathophysiology of myofascial pain syndrome (MPS), including alterations in redox status, inflammation, and the myofascial trigger point (MTrP) biochemical milieu, as well as imaging and neurophysiological outcomes. Finally, we discuss the long-term goal of conducting a Delphi survey, to assess the influence of putative MPS biomarkers on clinician opinion, in order to ultimately develop new criteria for the diagnosis of MPS.

RECENT FINDINGS

Myofascial pain syndrome (MPS) is a prevalent healthcare condition associated with muscle weakness, impaired mood, and reduced quality of life. MPS is characterized by the presence of myofascial trigger points (MTrPs): stiff and discrete nodules located within taut bands of skeletal muscle that are painful upon palpation. However, physical examination of MTrPs often yields inconsistent results, and there is no gold standard by which to diagnose MPS. The current MPS diagnostic paradigm has an inherent subjectivity and the absence of correlation with the underlying pathophysiology. Recent advancements in ultrasound imaging, systemic biomarkers, MTrP-specific biomarkers, and the assessment of dysfunction in the somatosensorial system may all contribute to improved diagnostic effectiveness of MPS.

Potential Role of MRI Imaging for Myofascial Pain: A Scoping Review for the Clinicians and Theoretical Considerations

The most common cause of chronic musculoskeletal pain is chronic myofascial pain syndrome (MPS). MPS often presents with increased muscle stiffness, and the myofascial trigger point (MTrP). Imaging modalities have been used to identify the MTrP, but their role in the detection and diagnosis of MPS remains unclear. The purpose of this review was to identify evidence in literature for the use of imaging in the role of classifying and explaining the physiology of MTrPs. Since few imaging techniques have been performed on MTrPs, we explored the imaging techniques that can effectively image complex skeletal muscle microstructure, and how they could be used. As part of a scoping review, we conducted a systematic search from three medical databases (CINAHL, EMBASE and MEDLINE) from year to year to analyze past MTrP imaging, as well as analyzing imaging techniques performed on the microstructure of muscle. Previously, ultrasound has been used to differentiate active, latent MTrPs, but these studies do not adequately address their underlying anatomical structure. MRI remains the standard method of imaging skeletal muscle. The existing MRI literature suggests that the DTI technique can quantify muscle injury, strain, and structure. However, theoretically, HARDI and DKI techniques seem to provide more information for complex structural areas, although these modalities have a disadvantage of longer scan times and have not been widely used on skeletal muscle. Our review suggests that DTI is the most effective imaging modality that has been used to define the microstructure of muscle and hence, could be optimal to image the MTrP. HARDI and DKI are techniques with theoretical potential for analysis of muscle, which may provide more detailed information representative of finer muscle structural features. Future research utilizing MRI techniques to image muscle are necessary to provide a more robust means of imaging skeletal muscle and the MTrP.

Is Dry Needling Applied by Physical Therapists Effective for Pain in Musculoskeletal Conditions? A Systematic Review and Meta-Analysis

OBJECTIVE

The main objective of this systematic review and meta-analysis was to determine the short-, medium-, and long-term effectiveness of dry needling (DN) applied by physical therapists to myofascial trigger points for the treatment of pain.

METHODS

PubMed, Scopus, SportDiscus, and Web of Science databases were searched from their inception to February 2020. Randomized controlled trials that compared DN with other treatments or placebo and measured pain with a visual analog Scale or another numerical pain rating scale were included. Two authors used a personalized form to collect the following data relevant to the objectives of the review from each article independently: study design, purpose, sample size, diagnosis, characteristics of DN intervention, characteristics of placebo intervention, outcome measures, period of assessment, body region, DN technique, and number of sessions. The initial search identified 1771 articles. After the selection, 102 articles were assessed for eligibility; 42 of these articles measuring pain were used for the meta-analysis. Four meta-analyses were performed according to the follow-up period from the last reported treatment.

RESULTS

This meta-analysis found a large effect to decrease pain within 72 hours (standardized mean difference [SMD] = -0.81; 95% CI = -1.21 to -0.40), a moderate effect in 1 to 3 weeks (SMD = -0.69; 95% CI = -1.02 to -0.35), a large effect in 4 to 12 weeks (SMD = -0.85; 95% CI = -1.30 to -0.40), and a large effect in 13 to 24 weeks (SMD = -0.81; 95% CI = -1.64 to -0.03). The risk of bias was generally low; however, the heterogeneity of the results downgraded the level of evidence.

CONCLUSIONS

Low-quality evidence that the immediate to 72-hour (large) effect, 4- to 12-week (large) effect, 13- to 24-week (large) effect, and moderate-quality 1- to 3-week (moderate) effect suggested that DN performed by physical therapists was more effective than no treatment, sham DN, and other therapies for reducing pain.

IMPACT

DN is commonly used by physical therapists to treat musculoskeletal pain, and it is very important for physical therapists to know the clinical conditions and time periods for which DN is effective in reducing pain in their patients.

Chronic Facial Pain: Trigeminal Neuralgia, Persistent Idiopathic Facial Pain, and Myofascial Pain Syndrome-An Evidence-Based Narrative Review and Etiological Hypothesis

Trigeminal neuralgia (TN), the most common form of severe facial pain, may be confused with an ill-defined persistent idiopathic facial pain (PIFP). Facial pain is reviewed and a detailed discussion of TN and PIFP is presented. A possible cause for PIFP is proposed. (1) Methods: Databases were searched for articles related to facial pain, TN, and PIFP. Relevant articles were selected, and all systematic reviews and meta-analyses were included. (2) Discussion: The lifetime prevalence for TN is approximately 0.3% and for PIFP approximately 0.03%. TN is 15-20 times more common in persons with multiple sclerosis. Most cases of TN are caused by neurovascular compression, but a significant number are secondary to inflammation, tumor or trauma. The cause of PIFP remains unknown. Well-established TN treatment protocols include pharmacotherapy, neurotoxin denervation, peripheral nerve ablation, focused radiation, and microvascular decompression, with high rates of relief and varying degrees of adverse outcomes. No such protocols exist for PIFP. (3) Conclusion: PIFP may be confused with TN, but treatment possibilities differ greatly. Head and neck muscle myofascial pain syndrome is suggested as a possible cause of PIFP, a consideration that could open new approaches to treatment.