Myofascial pain syndrome is a common nonarticular local musculoskeletal pain syndrome caused by myofascial trigger points located at muscle, fascia, or tendinous insertions, affecting up to 95% of people with chronic pain disorders. Clinically, myofascial pain syndrome can present as painful restricted range of motion, stiffness, referred pain patterns, and autonomic dysfunction. The underlying cause is often related to muscular imbalances, and following a thorough physical examination the condition should be treated with a comprehensive rehabilitation program. Additional treatment options include pharmacologic, needling with or without anesthetic agents or nerve stimulation, and alternative medicine treatments such as massage or herbal medicines. Repeated trigger point injections should be avoided, and corticosteroids should not be injected into trigger points.
Myofascial syndrome is a common nonarticular local musculoskeletal pain syndrome caused by myofascial trigger points (MTrPs) located at muscle, fascia, or tendinous insertions. Myofascial syndrome affects up to 95% of people with chronic pain disorders and has also been found to be the principal cause of pain in 85% of patients attending a pain center. As many as 9 million people in the United States suffer with myofascial pain. Initially described in the 16th century by the French physician de Baillou (who named this regional pain syndrome muscular rheumatism), this condition has received several terms throughout the years including idiopathic myalgia, regional fibromyalgia, and regional soft tissue pain, among others. It was not until the 1950s that Travell and Rinzler referred to these muscle pain patterns as myofascial pain.
Myofascial pain syndrome is characterized by the presence of trigger points, which are hyperirritable tender spots in palpable tense bands of skeletal muscles. Trigger points can be either active, which are tender and spontaneously painful, or latent, which are tender but not spontaneously painful. Snapping palpation of the taut bands may produce a transient contraction of a group of muscle fibers referred as the local twitch response. Local twitch response is caused by activation of local Ia afferents and consequent reflex response of α motor neurons, which indicates the presence of muscle spindles. A patient vocalization or withdrawal from palpation when exquisite tenderness is perceived is referred as the jump sign. Clinically, myofascial pain syndrome can present as painful restricted range of motion, stiffness, referred pain patterns, and autonomic dysfunction.
Pathophysiology
Several hypotheses proposed have been a topic of debate for the last several years. At present the most accepted theory is the Integrated Trigger Point Hypothesis described by Simons. Simons’ integrated hypothesis proposes that a sequence of events including an “energy crisis” of the muscle fibers will cause sustained sarcomere contracture. Decreased levels of adenosine triphosphate caused by reduced blood flow renders the muscle fibers with insufficient energy to return calcium to the sarcoplasmic reticulum, resulting in a rigor state where these muscle fibers are unable to relax. This situation leads to increased metabolic demands, resulting in local temporary hypoxia and the release of noxious histochemicals, which may account for the pain associated with the active MTrPs.
It has also been hypothesized that the reason for this sarcomere shortening is secondary to an increase in miniature endplate potentials and excessive acetylcholine release, the reason why botulinum toxin may be effective in the treatment of MTrPs. Besides the mechanism of excessive release of acetylcholine leading to abnormal depolarization, other mechanisms include upregulation of nicotinic acetylcholine-receptor activity as well as genetic or acquired defects of the L-type and N-type voltage-gated Ca 2+ channel. Excessive calcium release at the sarcoplasmic reticulum through a dysfunctional Ryanidine receptor calcium channel may also cause sustained muscle contraction.
Simons’ theory was supported by Shah and colleagues when they measured the levels of biochemical substances at active and latent MTrPs at the upper trapezius and compared them to uninvolved sites at the gastrocnemius muscle. These biochemical substances are associated with the pain, muscle soreness, and inflammation in the soft tissue sites. The selected inflammatory mediators include neuropeptides, cytokines, and catecholamines, and also noted is a decrease in pH. These chemical substances activate the different nociceptors located at muscle, fascia, and joints, and are responsible for the pain associated with the myofascial pain syndrome. Specific substances found by Shah and Gilliams in their study of microdialysis sampling of the trapezius include substance P, calcitonin gene-related peptide, serotonin, norepinephrine, prostaglandins, bradykinins, tumor necrosis factor α, interleukin (IL)-6, IL-8, and IL-1β. The acidic environment secondary to ischemia and local hypoxia inhibits acetylcholinesterase, resulting in an excess of acetylcholine, and activates nociceptors that promote hyperalgesia.
The vasodilatory effects of several of the biochemicals released contribute to increased pain at the active trigger point. Furthermore, Partanen and colleagues suggested in 2010 that postural stresses and sustained overload of the muscle will cause inflammation of the muscle spindles, resulting in activation and sensitization of intrafusal III and IV afferents.
The pain experienced by these patients may be severe only with minimal palpation, and they may appear as if they are overreacting. This pain response is felt to be secondary to hyperalgesia as a result of sensitization. Many of the endogenous substances mentioned may cause peripheral sensitization of nociceptors, which decrease their pain threshold in the peripheral receptors and cause a normally nonpainful stimulus to elicit pain.
Etiology
There are many factors that have been proposed to result in the development and persistence of MTrP pain. These factors include anatomic abnormalities, various postural habits, vocational activities causing excessive strain on a particular muscle, tendon, or ligament, endocrine dysfunctions, psychological stressors, sleep disorders, and lack of exercise.
Mechanical
Postural habits contribute to the development of myofascial pain by causing excessive overload on specific muscle groups, the quadratus lumborum being the most commonly involved. For example, leg crossing will cause the hemipelvis to rise, approximating the iliac crest to the 12th rib, and cause shortening of the ipsilateral quadratus lumborum. A common sleeping position such as lying on one’s side with the uppermost leg in adduction will also cause shortening of the quadratus lumborum, and these patients will typically complain that their pain is worse at night. Anatomic considerations include leg length inequality, short arms, and a small hemipelvis. Leg length discrepancy will cause excessive lumbar lordosis and excessive stress at the quadratus lumborum. The compensatory (functional) scoliosis produced by the quadratus lumborum is a necessary lumbar curvature needed to maintain balance, leading to overloading of this muscle. Patients with short arms can be identified by evaluating if the elbows do not reach the iliac crest. When seated, these patients will tend to slump forward or lean to one side of the chair, to be able to place their elbows at the armrest, resulting in excessive strain on the quadratus lumborum and posterior cervical paraspinal muscles. One can also see shoulder tilt to accommodate the spinal curvature and chronic muscle contraction to bring the spine back to midline, which will eventually lead to trigger points.
Medical
Besides mechanical causes of myofascial type pain such as structural, postural, or ergonomic; others include hormonal dysfunction, enzyme deficiencies, immunologic causes, infectious diseases, and nutritional deficiencies. Plotnikof and Quigley found that 89% of subjects with chronic musculoskeletal pain had low levels of vitamin D. Deficiency of this vitamin has been associated with musculoskeletal pain, loss of type II fibers, and proximal muscle atrophy. Vitamin B12 and iron deficiency have also been linked to chronic pain, presenting with symptoms such as muscle pain, chronic fatigue, tiredness, and poor endurance. Iron is necessary for the generation of energy through the cytochrome oxidase system, and a deficiency of accessible iron in muscle will result in “energy crisis.” Other vitamins such as vitamins C, B1, and B6 have also been associated with diffuse mylagia.
Endocrine disorders include hypothyroidism and growth hormone deficiency. Special considerations have been made with hypothyroidism in view of that it promotes a hypometabolic state thought to promote trigger point formation. Low levels of thyroid hormones will affect cellular metabolism, resulting in an inadequate supply of energy for muscle contraction. The same principle of active muscle contraction secondary to inadequate recovery of calcium by the sarcoplasmic reticulum is also seen in McArdle disease. This genetic myophosphorylase deficiency will affect glycolytic metabolism in muscle and will lead to lack of calcium recovery. Finally, infections that have been linked to myofascial pain include chronic Lyme disease, chronic mycoplasma infections, hepatitis C, and enteroviruses.
Assessment
Identification of MTrPs is almost entirely based on history and physical examination. The patient will usually present with a chronic history of localized or regional pain, with resisted range of motion of the muscles involved. It is essential to identify from the history if the muscle pain is more focal as opposed to generalized or widespread. A focal myalgia would suggest mechanical or structural factors as the cause of pain, whereas in a widespread myalgia, laboratory tests are necessary to identify metabolic, hormonal, or nutritional disorders, or fibromyalgia as the reason for the musculoskeletal pain syndrome. There are also a series of diagrams that the patient can use to identify his or her pain pattern, for a better assessment of widespread versus localized pain.
Physical examination should begin inspecting for postural imbalances, gait, pelvic symmetry, shoulder tilt, leg length discrepancies, and for compensatory functional scoliosis. Evaluating tightness at the hip flexors and hamstrings should be part of the physical examination, as tightness in these muscle groups will promote forward pelvic tilt and an increase in lumbar lordosis, which will result in excessive strain at extensor muscles. Palpation is the most important component of the physical examination to assess for the presence of MTrPs. It is essential to identify if the tender points on palpation produce referred pain patterns or just local tenderness, which is the main difference between trigger points and tender spots. A systematic review in 2009 by Lucas and colleagues on the reliability of physical examination for the diagnosis or trigger points demonstrated that due to a lack of studies and interobserver reliability, physical examination cannot currently be recommended as a reliable test for the diagnosis of trigger points.
When evaluating patients with suspected myofascial low back pain, muscles that may have trigger points include the iliocostalis lumborum, longissimus thoracis, multifidus, quadratus lumborum, and gluteus medius. Travell and Simons suggest that the quadratus lumborum and gluteus medius are the most frequently involved. Adequate assessment of the quadratus lumborum will require that the patient be lying on his or her side with the uppermost arm abducted above the head with knees bent. Palpation of the gluteus medius should be at the upper lateral quadrant of the buttocks when the patient is lying prone. In a prospective study by Njoo and Van der Does, it was determined that the clinical usefulness of trigger points is increased when localized tenderness and the presence of either the jump sign or patient’s recognition of his pain pattern are used as criteria for the presence of trigger points in these muscles.
Also, adequate screening for stress and anxiety is important in patients with widespread musculoskeletal pain. Severe depression, anxiety, and fear avoidance behavior are predominantly associated with patients with low back pain and widespread musculoskeletal pain as compared with patients who are pain free. Other psychosocial factors to consider include low income, early psychological stressors, gender, job satisfaction, and history of musculoskeletal pain in family members.
Etiology
There are many factors that have been proposed to result in the development and persistence of MTrP pain. These factors include anatomic abnormalities, various postural habits, vocational activities causing excessive strain on a particular muscle, tendon, or ligament, endocrine dysfunctions, psychological stressors, sleep disorders, and lack of exercise.
Mechanical
Postural habits contribute to the development of myofascial pain by causing excessive overload on specific muscle groups, the quadratus lumborum being the most commonly involved. For example, leg crossing will cause the hemipelvis to rise, approximating the iliac crest to the 12th rib, and cause shortening of the ipsilateral quadratus lumborum. A common sleeping position such as lying on one’s side with the uppermost leg in adduction will also cause shortening of the quadratus lumborum, and these patients will typically complain that their pain is worse at night. Anatomic considerations include leg length inequality, short arms, and a small hemipelvis. Leg length discrepancy will cause excessive lumbar lordosis and excessive stress at the quadratus lumborum. The compensatory (functional) scoliosis produced by the quadratus lumborum is a necessary lumbar curvature needed to maintain balance, leading to overloading of this muscle. Patients with short arms can be identified by evaluating if the elbows do not reach the iliac crest. When seated, these patients will tend to slump forward or lean to one side of the chair, to be able to place their elbows at the armrest, resulting in excessive strain on the quadratus lumborum and posterior cervical paraspinal muscles. One can also see shoulder tilt to accommodate the spinal curvature and chronic muscle contraction to bring the spine back to midline, which will eventually lead to trigger points.
Medical
Besides mechanical causes of myofascial type pain such as structural, postural, or ergonomic; others include hormonal dysfunction, enzyme deficiencies, immunologic causes, infectious diseases, and nutritional deficiencies. Plotnikof and Quigley found that 89% of subjects with chronic musculoskeletal pain had low levels of vitamin D. Deficiency of this vitamin has been associated with musculoskeletal pain, loss of type II fibers, and proximal muscle atrophy. Vitamin B12 and iron deficiency have also been linked to chronic pain, presenting with symptoms such as muscle pain, chronic fatigue, tiredness, and poor endurance. Iron is necessary for the generation of energy through the cytochrome oxidase system, and a deficiency of accessible iron in muscle will result in “energy crisis.” Other vitamins such as vitamins C, B1, and B6 have also been associated with diffuse mylagia.
Endocrine disorders include hypothyroidism and growth hormone deficiency. Special considerations have been made with hypothyroidism in view of that it promotes a hypometabolic state thought to promote trigger point formation. Low levels of thyroid hormones will affect cellular metabolism, resulting in an inadequate supply of energy for muscle contraction. The same principle of active muscle contraction secondary to inadequate recovery of calcium by the sarcoplasmic reticulum is also seen in McArdle disease. This genetic myophosphorylase deficiency will affect glycolytic metabolism in muscle and will lead to lack of calcium recovery. Finally, infections that have been linked to myofascial pain include chronic Lyme disease, chronic mycoplasma infections, hepatitis C, and enteroviruses.
Assessment
Identification of MTrPs is almost entirely based on history and physical examination. The patient will usually present with a chronic history of localized or regional pain, with resisted range of motion of the muscles involved. It is essential to identify from the history if the muscle pain is more focal as opposed to generalized or widespread. A focal myalgia would suggest mechanical or structural factors as the cause of pain, whereas in a widespread myalgia, laboratory tests are necessary to identify metabolic, hormonal, or nutritional disorders, or fibromyalgia as the reason for the musculoskeletal pain syndrome. There are also a series of diagrams that the patient can use to identify his or her pain pattern, for a better assessment of widespread versus localized pain.
Physical examination should begin inspecting for postural imbalances, gait, pelvic symmetry, shoulder tilt, leg length discrepancies, and for compensatory functional scoliosis. Evaluating tightness at the hip flexors and hamstrings should be part of the physical examination, as tightness in these muscle groups will promote forward pelvic tilt and an increase in lumbar lordosis, which will result in excessive strain at extensor muscles. Palpation is the most important component of the physical examination to assess for the presence of MTrPs. It is essential to identify if the tender points on palpation produce referred pain patterns or just local tenderness, which is the main difference between trigger points and tender spots. A systematic review in 2009 by Lucas and colleagues on the reliability of physical examination for the diagnosis or trigger points demonstrated that due to a lack of studies and interobserver reliability, physical examination cannot currently be recommended as a reliable test for the diagnosis of trigger points.
When evaluating patients with suspected myofascial low back pain, muscles that may have trigger points include the iliocostalis lumborum, longissimus thoracis, multifidus, quadratus lumborum, and gluteus medius. Travell and Simons suggest that the quadratus lumborum and gluteus medius are the most frequently involved. Adequate assessment of the quadratus lumborum will require that the patient be lying on his or her side with the uppermost arm abducted above the head with knees bent. Palpation of the gluteus medius should be at the upper lateral quadrant of the buttocks when the patient is lying prone. In a prospective study by Njoo and Van der Does, it was determined that the clinical usefulness of trigger points is increased when localized tenderness and the presence of either the jump sign or patient’s recognition of his pain pattern are used as criteria for the presence of trigger points in these muscles.
Also, adequate screening for stress and anxiety is important in patients with widespread musculoskeletal pain. Severe depression, anxiety, and fear avoidance behavior are predominantly associated with patients with low back pain and widespread musculoskeletal pain as compared with patients who are pain free. Other psychosocial factors to consider include low income, early psychological stressors, gender, job satisfaction, and history of musculoskeletal pain in family members.
Myofascial pain versus fibromyalgia
Common differential diagnoses of low back pain include mechanical, sacroiliac joint, discogenic or zygapophysial joint pain; a thorough physical examination will help rule out most of these. When considering myofascial low back pain as the cause of the patient’s complaint; special attention has to be made to fibromyalgia, which is also a chronic noninflammatory muscle pain syndrome. Many questions have risen over the years regarding the diagnosis of fibromyalgia, and several have doubted its existence.
Fibromyalgia is a syndrome characterized by chronic widespread muscle tenderness as a result of widespread sensitization. Fibromyalgia may be accompanied by fatigue, sleep disturbances, mood disturbances, depression, and visceral pain syndromes.
The current American College of Rheumatology (ACR) criteria include spontaneous pain present for over 3 months, pain in all 4 quadrants of the body (above and below the waist, right and left of midline) and pain on digital palpation on 11 out of 18 tender points. Without an adequate physical examination one might confuse myofascial pain syndrome with fibromyalgia. Myofascial pain syndrome is the most common condition that must be considered in the differential diagnosis of fibromyalgia and can also present as widespread myalgia. As stated in a review by Gerwin in 2005 about myofascial pain syndrome and fibromyalgia; “many cases of fibromyalgia are in fact cases of myofascial pain syndrome that have been misdiagnosed as a result of poor muscle palpation techniques that miss the presence of taut bands and referred pain.” The main difference between the two is the referral of pain produced when palpating trigger points as compared with tender spots.
In previous studies more than 10 active trigger points were found in more than half of fibromyalgia patients, and active trigger points were found in about 18% of examinations in the predetermined tender points of fibromyalgia. A study by Ge and colleagues in 2009 evaluated if the predetermined sites of examination for tender points in fibromyalgia were frequently associated with MTrPs. Thirty women diagnosed with fibromyalgia as per the ACR criteria were chosen for the study. All of the 18 predetermined tender points were manually palpated and examined with intramuscular needle electromyographic (EMG) examination, as one would expect to see spontaneous electric activity in both active and latent trigger points. The 2 sites bilaterally at the second rib were not included in the EMG examination of thin patients, to avoid any complications. In this study more than 90% of the predetermined tender point sites were either active or latent MTrPs, as evaluated by manual palpation and confirmed by needle EMG registration of spontaneous electrical activity. In conclusion, this study demonstrated that positive tender points at predetermined sites were mostly clinically active and latent trigger points at these predetermined sites, which mimicked fibromyalgia pain.
A new diagnostic tool named the Symptom Intensity Scale (SIS) has been developed for the diagnosis of fibromyalgia. This tool has been used to both diagnose and establish severity of fibromyalgia, without the need to count tender points. The scale consists of 2 parts: a regional pain score, which is the number of anatomic areas out of possible 19 in which the patient feels pain, and a fatigue visual analog scale whereby the patient makes a mark somewhere along a 10-cm line to indicate how tired they are. The SIS has been shown to be an accurate measure for general health, depression, and disability. Although still not recognized by the ACR, several investigators state that it will probably replace the current diagnostic criteria and that tender spots will no longer have to be counted.
Diagnostic criteria for myofascial pain syndrome
Travell and Simons are identified as the principal founders of the diagnostic criteria of myofascial pain. Their proposed criteria include tender spots in a taut band, predicted pain referral pattern, patient pain recognition on tender point palpation, limited range of motion, and the local twitch response. A literature review from 2007 examined the variability of criteria used to diagnose MTrP pain syndrome. The criteria most commonly used by researchers and expert clinicians include all of the previously mentioned by Travell and Simons, except the local twitch response, which has not shown to be a reliable diagnostic test. When comparing the frequency of the commonly used criteria, identifying a tender spot in a taut band is used in 65% of cases, and had been suggested by Travell and Simons to be the most sensitive and specific of all the diagnostic criteria. The frequency of the criteria used include patient pain recognition 53%, predicted pain referral pattern 44%, local twitch response 44%, and limited range of motion 22%. There is still a lack of evidence demonstrating the reliability of these maneuvers. Further research is needed to test the sensitivity, specificity, and reliability of the current diagnostic criteria.
Other minor criteria proposed include the jump sign, muscle weakness, autonomic responses, reduced skin resistance, pressure algometry readings, patients’ being able to identify their trigger points, and alleviation of symptoms by stretch. The combination of the criteria used has been inconsistent but the combination proposed by Simons is still the most commonly used. The most recent modifications of the diagnostic criteria include tender spot in a taut band, patient pain recognition, and painful limitation to range of motion.
The local twitch response and predicted pain referral pattern are no longer considered as part of the diagnosis. Other investigators have suggested alleviation of the pain by infiltration of a local anesthetic and pressure algometry readings as part of the diagnosis, but this has not been adopted by many. In a 2009 review of the reliability of physical examination for the diagnosis of MTrPs, firm digital pressure and the patient’s feedback on the pain experience are considered the best indicators of the presence of trigger points. In this same review it was concluded that no study to date has reported the reliability of trigger point diagnosis according to the currently proposed criteria in symptomatic patients. Ongoing microdialysis and EMG studies will continue to define and validate the current proposed criteria. There is still poor agreement among investigators as to the most appropriate diagnostic criteria; only recently have interrater reliability studies been reported.
It is well known that the pressure algometer is used by manual medicine practitioners to determine the pressure pain threshold of specific muscles, joints, tendons, ligaments, and bones. The pressure algometer measures the force in pounds or kilograms required to produce pain, and has become useful to quantify pain and track recovery. It is a hand-held instrument with a 1-cm 2 surface area plunger attached to a dynamic force gauge that may be used to assess sensitivity to pressure near a trigger point. Some studies have found high validity with an excellent inter- and intrarater reliability, but algometry is more commonly used in a research setting than clinical practice. Other studies have demonstrated that the pressure algometer may have limited validity on determining pressure pain thresholds. Recently a new muscle pain detection device (MPDD) has been developed for identification of trigger points that will also distinguish between primary and referred muscle pain. This new device elicits contractions in muscles in an attempt to identify the muscle pain generator (see the next section for more details).
Related posts:
Functional Anatomy and Pathophysiology of Axial Low Back Pain: Disc, Posterior Elements, Sacroiliac Joint, and Associated Pain Generators
Electrodiagnostics for Low Back Pain
Imaging the Back Pain Patient
Epidural Steroid Injections for Low Back Pain
Sacroiliac Joint and Lumbar Zygapophysial Joint Corticosteroid Injections
The Use of Spinal Cord Stimulation and Intrathecal Drug Delivery in the Treatment of Low Back-Related Pain
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