Scientific Paper: The Myofascial Conundrum - Reconciling Emerging Science with Clinical Practice

Objectives
Chronic myofascial pain syndrome (cMPS) represents the most common cause of chronic musculoskeletal pain. With the rapidly aging demographic, there exists a timely and urgent need to advance mechanism-based diagnostic and therapeutic strategies to manage this growing burden effectively. The current prevailing consensus suggests that local mechanical injury is the precipitating factor in the pathogenesis of cMPS. This review examines the major limitations of this muscle-centric paradigm by highlighting several clinical features of cMPS that cannot be reconciled using a local injury framework. We synthesize emerging neurophysiological, imaging, and epidemiological evidence to propose alternative explanations based in first-principles of neurobiology to advance a more evidence-based pathophysiological framework that aligns with clinical observation and directly informs novel, mechanism-guided approaches to diagnosis and treatment of cMPS.

Design
This paper employed a narrative review methodology, in combination with theoretical reconceptualization, to critically synthesize the existing literature on chronic myofascial pain syndrome (cMPS). The approach involved a comprehensive literature search across databases including PubMed, Scopus, and Web of Science, utilizing keywords such as "myofascial pain," "neurogenic inflammation," "central sensitization," "myofascial trigger points." Inclusion criteria prioritized peer-reviewed articles from the last two decades, encompassing preclinical animal models and clinical cohort studies. The synthesis aimed to integrate these clinical paradoxes unresolved by current muscle-centric mechanical injury paradigms with emerging evidence from observational and experimental studies informing novel directions in the pathogenesis of cMPS.

Results
The prevailing mechanical overload hypothesis fails to explain hallmark features of cMPS, including diffuse, non-noxious pain that patients report as relieving, absence of protective nociceptive withdrawal responses, presence of allodynia and autonomic disturbances disproportionate to identifiable muscle injury, and transient responses to targeted peripheral trigger-point interventions.

Emerging evidence supports an updated neurogenic paradigm whereby persistent low-grade nociceptive input from segmental structures (e.g., degenerative joints or viscera) drives central sensitization. This triggers retrograde release of substance P and CGRP, inducing neurogenic inflammation and nociceptor sensitization within corresponding myotomes and fascia. Clinically, this manifests as palpable myofascial trigger-points and taut bands, suggestive of secondary epiphenomena rather than primary pathology.

Clinical cohorts reveal comorbidity between osteoarthritis and MTrP, whereas animal models demonstrate neurogenic inflammation within segmentally related myotomes following experimentally induced spinal osteoarthritis. These findings imply that cMPS may be a centrally-maintained, neurogenically-driven secondary condition, as opposed to a primary nociceptive manifestation.

Conclusions
The emerging evidence points to a fundamental role of neurogenic inflammation in the pathogenesis of cMPS. The comorbidity of cMPS with OA, and the emergence of robust evidence demonstrating neurogenic inflammation following the induction of experimental osteoarthritis, offers a biologically plausible rationale for the pathogenesis of cMPS that resolves longstanding clinical paradoxes. These studies mark a potential paradigm shift of immediate practical diagnostic and therapeutic value that should be further advanced. Under this framework, effective clinical management of cMPS necessitates a systematic assessment for underlying degenerative spine/joint disease as a potential primary nociceptive driver in non-specific myofascial pain phenotypes. Treatment must address both the osteoarthritic source while simultaneously targeting central sensitisation through a multimodal approach including various modalities (dry needle, ultrasound, manual therapies), centrally acting medication, education, graded exercise and cognitive-behavioural intervention.

Chronic myofascial pain syndrome (cMPS) is the most prevalent form of chronic musculoskeletal pain, affecting up to 30% of adults and more than 85% of individuals over age 65, with an annual economic burden in the United States alone estimated at $560–635 billion. Despite its enormous clinical and socioeconomic impact, the pathophysiology of cMPS remains poorly understood. No reliable diagnostic laboratory or imaging tests exist, with diagnosis of cMPS relying primarily on clinical history and palpation of myofascial trigger points (MTrPs). These hyperirritable nodules, located within taut bands of skeletal muscle, have been shown to refer pain, elicit local twitch responses, and exhibit distinct electrophysiological, biochemical, sonographic, and mechanical properties versus normal muscle.

The prevailing theoretical model of cMPS proposes that MTrPs arise primarily from mechanical overload injury to the myotendinous unit. This local injury is thought to produce dysfunctional endplates, spontaneous electrical activity, excessive calcium release, persistent sarcomere contracture, local ischemia, and an “energy crisis” perpetuated by inflammatory mediators and sensitizing substances. Although this framework integrates mechanical, biochemical, and neurological factors, several fundamental clinical observations remain irreconcilable with a muscle-centric, primary peripheral injury mechanism.

First, cMPS and MTrP frequently co-occur with visceral disorders including endometriosis, prostatitis, irritable bowel syndrome and cholecystitis, often in the absence of direct trauma to the affected muscles. Similar associations exist with somatic conditions such as discopathy, arthritis, and joint dysfunction without evidence of local muscle injury. These consistent viscerosomatic and somatovisceral relationships strongly suggest that MTrPs may be secondary manifestations of an underlying pathology, rather than representing a primary pathology themselves.

Second, the pain quality in cMPS differs markedly from acute nociceptive pain typically following muscle injury. Patients describe cMPS as deep, dull, diffuse, and non-noxious, often accompanied by regional allodynia, motor dysfunction, and autonomic disturbances. Furthermore, many patients with true cMPS fail to demonstrate a nociceptive withdrawal response following pressure to a MTrP locus. In contrast to the sharp, well-localized, noxious pain of acute injury, pressure applied to an MTrP is frequently perceived as “soothing,” “relieving,” or “good” pain, prompting patients to seek deeper and sustained compression for relief. This paradoxical response stands in opposition to the protective withdrawal reflex expected from a site of primary tissue damage.

Third, stimulus intensity-pain response in cMPS reveals a linear rather than the typical power-function profile, with discomfort or pain (allodynia) occurring at lower pressure thresholds. Neurophysiologically, this pattern reflects a qualitative shift from high-threshold nociceptor (Aδ/C-fiber) dominance to greater contribution from large-diameter, low-threshold myelinated mechanoreceptors. These large myelinated fibers are the same afferents that mediate non-noxious sensations within zones of secondary hyperalgesia, suggesting that the pain of cMPS is not simply amplified nociception but a fundamentally altered sensory experience driven predominantly by maladaptive central sensitization.

Collectively, these discrepancies cannot be adequately explained using a muscle-centric primary peripheral injury model focused on the MTrP as the primary nociceptive source of cMPS. Instead, they point to cMPS as a centrally mediated neurogenic disorder in which MTrPs reside within regions of secondary hyperalgesia, caused by central sensitization and downstream effects of neurogenic inflammation. The authors propose a fundamental paradigm shift that reconceptualizes cMPS using first-principles of neurobiology, moving away from the traditional mechanical injury/energy-crisis construct toward a neurogenic hypothesis rooted in central sensitization and neurogenic inflammation. In this emerging framework, sustained nociceptive input from visceral, somatic, or psychological sources may drive or contribute to central sensitization, lowering activation thresholds for wide-dynamic-range and nociceptive-specific neurons. Descending facilitation and loss of inhibition amplify and maintain this central hyperexcitability, which in turn triggers peripheral neurogenic inflammatory responses via antidromic release of proinflammatory neuropeptides (Substance P, CGRP) into neurosegmentally linked myotomes to produce regions of secondary hyperalgesia. These neuropeptides, in turn, trigger vasodilation, plasma extravasation, and sensitization of muscle nociceptors, manifesting clinically as taut bands, contractile nodules, and referred pain zones. Recent human observational studies and emerging experimental evidence using animal models suggests that degenerative spine and joint disease may be important primary pathologies driving neurogenic inflammatory mechanisms in the pathogenesis of cMPS.

This neurogenic model accounts for the many observed clinical paradoxes. Using this framework, (1) visceral disorders can generate MTrPs without direct muscle trauma via viscerosomatic convergence, central sensitization and neurogenic inflammation to produce regions of secondary hyperalgesia; (2) non-noxious, soothing pressure on MTrPs may activate low-threshold mechanoreceptors to produce non-noxious allodynic sensations typical of cMPS; (3) the linear stimulus-response profile in cMPS is explained by the dominant input from large myelinated afferents within secondary hyperalgesic zones; and (4) absence of exaggerated NWR is expected because the MTrP lies within regions of secondary hyperalgesia, rather than regions of primary (injury-induced) hyperalgesia.

By resolving the longstanding dichotomy between prevailing theory and clinical observation, the neurogenic hypothesis of cMPS offers a mechanism-based framework that aligns with contemporary pain neurobiology. It shifts clinical focus from local MTrP inactivation alone toward comprehensive strategies targeting central sensitization (pharmacological, cognitive-behavioral, and neuromodulatory) while employing therapeutic interventions (manual and needling techniques) for central gating effects. Future research must aim to validate objective biomarkers of neurogenic inflammation and central sensitization in cMPS, refine diagnostic criteria, and develop targeted therapies that address the root neurobiological drivers rather than peripheral manifestations alone. Such a paradigm shift will inform advances in both diagnostic and therapeutic approaches for cMPS, with an aim to reducing the growing personal and societal burden of this pervasive yet misunderstood condition.