Myofascial pain researchUncovering the biochemical milieu of myofascial trigger points using in vivo microdialysis: An application of muscle pain concepts to myofascial pain syndrome
Introduction
Myofascial pain syndrome (MPS) is a major progenitor of non-articular local musculoskeletal pain and tenderness that affects every age group, and is commonly recognized as “muscle knots” (Kao et al., 2007). MPS has been associated with numerous pain conditions including radiculopathies, joint dysfunction, disk pathology, tendonitis, craniomandibular dysfunction, migraines, tension-type headaches, carpal tunnel syndrome, computer-related disorders, whiplash-associated disorders, spinal dysfunction, and pelvic pain and other urologic syndromes, post-herpetic neuralgia, and complex regional pain syndrome (Borg-Stein and Simons, 2002).
Characterized by a physical finding and symptom cluster, MPS lacked demonstrable pathology and attracted little research attention until recently. Although the specific pathophysiological basis of MTrP development and symptomatology is unknown, several promising lines of scientific study (i.e. histological, neurophysiological, biochemical, and somatosensory) have revealed objective abnormalities (Reitinger et al., 1996; Windisch et al., 1999; Mense, 2003; Shah et al., 2005, Shah et al., 2008; Kuan et al., 2007; Niddam et al., 2007). These findings suggest that myofascial pain is a complex form of neuromuscular dysfunction consisting of motor and sensory abnormalities involving both the peripheral and central nervous systems. MPS is not to be confused with fibromyalgia syndrome, which is ascribed to a collection of complaints including chronic widespread pain, accompanied by tactile allodynia, fatigue, sleep disturbance, and psychological distress (Wolfe et al., 1990).
Section snippets
Historical terminology
Since muscle pain and particularly MPS is described as diffuse and can often refer to deep somatic tissue, terminology regarding muscle pain has been controversial. The first descriptions of “muscular rheumatism” were made by a French physician, de Baillou, in the 16th century (Stockman, 1904). Later observations by the British physician Balfour in 1816 described nodular tumors and thickenings (Stockman, 1904). In the early 20th century, literature on muscle pain used several terms that
Myofascial trigger point diagnostic criteria
Myofascial pain is identified by palpating skeletal muscle for myofascial trigger points (MTrPs). A MTrP is classically defined by Simons and Travell as “a hyperirritable spot in skeletal muscle that is associated with a hypersensitive palpable nodule in a taut band” (Simons et al., 1999). Figure 1 illustrates the trigger point complex. MTrPs are sensitive to pressure and are stiffer than surrounding tissue. Palpation of a MTrP produces local pain and sensitivity, as well as diffuse and
Electrophysiology
The pathophysiology of MTrPs is incompletely understood. MTrPs are hypothesized to be a result of physiological dysfunction within the neuromuscular junction and the surrounding connective tissue. There is evidence that motor endplates of neurons terminating at the muscle fibers of a MTrP have abnormal activity. Electromyographic studies have revealed spontaneous electrical activity (SEA) generated at MTrP loci that was not seen in surrounding tissue (Hubbard and Berkoff, 1993). Originally
Nociceptor properties
Sensory processing and pain perception are key aspects in the description of MPS, along with the abnormal motor findings mentioned above. Transduction of local pain sensation often begins with the sensitization and activation of nociceptive sensory receptors. Nociceptors are located at free nerve endings in muscle, joint, skin, viscera, and blood vessels. Furthermore, muscle nociceptors may make up 50% of the composition of muscle nerves (Willard, 2008). The abundance of these nociceptors may
Uncovering the biochemical milieu of myofascial trigger points
We developed a microanalytical system to sample the unique biochemical milieu of substances related to pain and inflammation in muscle tissue with and without MTrPs (Shah et al., 2005). This system employed a minimally invasive 30-gauge needle capable of in vivo collection of small volumes (∼0.5 μl) at sub nanogram levels (<75 kDa). The needle (Figure 4) has the same size and shape as an acupuncture needle and allows simultaneous sampling of skeletal muscle tissue when an LTR is elicited by
pH
Acidic pH levels within muscle have been shown to be associated with pain and lowered nociceptor threshold sensitivity (Issberner et al., 1996). This association is supported by the microdialysis studies above, which found acidic pH levels in muscles containing active (painful) MTrPs. In a study of mouse model hyperalgesia, Sluka et al. (2001) showed that unilateral injections of acidic saline into the gastrocnemius resulted in long-lasting bilateral mechanical hyperalgesia. Contralateral
Conclusion
Myofascial trigger points are a very common and complex component of non-articular musculoskeletal pain and dysfunction. However, they are also regularly found in asymptomatic individuals. Therefore, our studies sought to determine if there are biochemical aspects that differentiate active MTrPs from latent MTrPs, and muscle without MTrPs. Our microanalytical technique permits direct sampling of the biochemical milieu of MTrPs, including bioactive substances (e.g., inflammatory mediators,
References (60)
- et al.
Muscle inflammation induces a rapid increase in calcitonin gene-related peptide (CGRP) mRNA that temporally relates to CGRP immunoreactivity and nociceptive behavior
Neuroscience
(2006) - et al.
Injection of adjuvant but not acidic saline into craniofacial muscle evokes nociceptive behaviors and neuropeptide expression
Neuroscience
(2007) Myofascial pain syndromes and their evaluation
Best Practice & Research Clinical Rheumatology
(2007)- et al.
Sense and specificity: a molecular identity for nociceptors
Current Opinion in Neurobiology
(1999) - et al.
Phentolamine effect on the spontaneous electrical activity of active loci in a myofascial trigger spot of rabbit skeletal muscle
Archives of Physical Medicine and Rehabilitation
(1998) - et al.
Cell damage excites nociceptors through release of cytosolic ATP
Pain
(2002) - et al.
TNF-[alpha] and IL-1[beta] mediate inflammatory hypernociception in mice triggered by B1 but not B2 kinin receptor
European Journal of Pharmacology
(2007) - et al.
Functional reorganization in the rat dorsal horn during an experimental myositis
Pain
(1994) Myofascial trigger points: the current evidence
Physical Therapy in Sport
(2004)- et al.
Pain due to tissue acidosis: a mechanism for inflammatory and ischemic myalgia?
Neuroscience Letters
(1996)
Myofascial trigger points in early life
Archives of Physical Medicine and Rehabilitation
The spinal cord connections of the myofascial trigger spots
European Journal of Pain
Cytokine profiles during carrageenan-induced inflammatory hyperalgesia in rat muscle and hind paw
The Journal of Pain
Tumour necrosis factor-[alpha], interleukin-1[beta] and interleukin-8 induce persistent mechanical nociceptor hypersensitivity
Pain
Biochemicals associated with pain and inflammation are elevated in sites near to and remote from active myofascial trigger points
Archives of Physical Medicine and Rehabilitation
Review of enigmatic MTrPs as a common cause of enigmatic musculoskeletal pain and dysfunction
Journal of Electromyography and Kinesiology
Substance P
European Journal of Pain
Ultrastructural changes in the rat phrenic nucleus developing within 2 h after cervical spinal cord hemisection
Experimental Neurology
Myofascial trigger point development from visual and postural stressors during computer work
Journal of Electromyography and Kinesiology
Hypernociceptive role of cytokines and chemokines: targets for analgesic drug development?
Pharmacology & Therapeutics
Focused review: myofascial pain
Archives of Physical Medicine and Rehabilitation
The effects of noradrenaline on the amplitude–time characteristics of multiquantum endplate currents and the kinetics of induced secretion of transmitter quanta
Neuroscience and Behavioral Physiology
Inhibitory effect of dry needling on the spontaneous electrical activity recorded from myofascial trigger spots of rabbit skeletal muscle
American Journal of Physical Medicine & Rehabilitation
Trigger point dry needling
The Journal of Manual & Manipulative Therapy
The importance of postural habits in perpetuating myofascial trigger point pain
Acupuncture in Medicine
An expansion of Simons’ integrated hypothesis of trigger point formation
Current Pain and Headache Reports
Serotonin 5-HT3 receptor mediation of pain and anti-nociception: implications for clinical therapeutics
Pain Physician
Ny forklaringsmodell for muskelskador vid statisk belastnin i skuldra och nacke [Swedish; New explanation for muscle damage as a result of static loads in the neck and shoulder]
Arbete Manniska Miljo
Lidocaine injection versus dry needling to myofascial trigger point: the importance of the local twitch response
American Journal of Physical Medicine and Rehabilitation
Cited by (232)
Comparing the remote effects of dry needling and ischemic pressure on pain intensity and threshold of the myofascial trigger points in women: A Single Blinded Randomized Clinical Trial
2024, International Journal of Osteopathic MedicineExamination of Dry Needling Dose and Effect Duration for Individuals With Chronic Ankle Instability
2023, Journal of Manipulative and Physiological TherapeuticsDry needling in the management of tendinopathy: A systematic review of randomized control trials
2023, Journal of Bodywork and Movement TherapiesAssociations Between Gluteus Medius Trigger Points With Hip Passive Range of Movement and Muscle Strength in Adults With Chronic Nonspecific Low Back Pain: A Cross-Sectional Study
2022, Journal of Manipulative and Physiological Therapeutics