Monday, October 20, 2008

Understanding Myofascial Pain

It has been estimated that some 44 million Americans have myofascial pain problems (1). A study from an internal medicine group practice found that 30% of patients with pain complaints had active myofascial trigger points (2). A report from a clinic specializing in head and neck pain reported a myofascial etiology in 55% of cases (3). Patients evaluated in one pain management center were found to have a myofascial component to their pain in 95% of cases (4). There is increasing awareness that active myofascial trigger points often play a role in the symptoms of patients with tension headaches (5), low back pain, neck pain (6), temporomandibular pain (7), forearm and hand pain (8), postural pain (9), pelvic/urogenital pain syndromes.
In interpreting the results of prevalence studies, it is important to distinguish between active myofascial trigger points and latent myofascial trigger points. Latent myofascial trigger points are defined as tender areas in muscle, in association with the other clinical features of the trigger point (see table 1), in the absence of associated pain syndrome. Active myofascial trigger points are associated with a pain syndrome that is reproduced by firm palpation of the trigger area.
For instance, Sola found latent trigger points in the shoulder girdle muscles of 54% of female and 45% of male subjects who were completely asymptomatic (10).
There have been no prevalence studies of myofascial pain syndromes in the context of rheumatology practice, but it is the author's experience that myofascial pain problems are often undiagnosed / untreated components of pain in osteoarthritis, rheumatoid arthritis, systemic lupus and other common rheumatic disorders.
The clinical diagnosis of myofascial pain is critically dependent on your doctor being aware of this diagnosis as a possible cause for some of your pain (11). Myofascial pain syndromes may mimic a large number of other disorders, thus there is a necessity to perform a thorough physical examination, with appropriate investigations. Myofascial pain characteristically presents as a dull deep aching sensation which is aggravated by use of the involved muscles as well as psychological stressors that cause increased muscle tension (12). The defining clinical characteristic of myofascial pain is the finding of a trigger point. This is a well-defined point of focal tenderness within a muscle. Sometimes firm palpation of this focus elicits pain in a referred distribution that reproduces the patient’s symptoms. Importantly, referred pain from a trigger point does not follow a nerve root distribution (i.e. it is not dermatomal). Palpation usually reveals a ropelike induration of the associated muscle fibers, often referred to as the “taut band”. Sometimes, snapping this band or needling the trigger point produces a localized twitch response of the involved muscle. This twitch response can only be reproducibly elicited in fairly superficial muscles.
Myofascial pain often results from muscle injury or repetitive strain. In the current medical climate, especially in United States, a whole array of often expensive investigations have usually been undertaken before the possibility of a myofascial pain diagnosis is considered. Some patients, who already have a well-defined cause for their musculoskeletal pain (e.g. rheumatoid arthritis), may develop a myofascial pain syndrome that goes unrecognized, as it is assumed that all their pain emanates from their primary diagnosis. Myofascial pain has certain clinical characteristics that aid in considering this diagnosis. The pain is typically described as a deep aching sensation, often with a feeling of stiffness in the involved area; this is sometimes described in terms of joint stiffness. Myofascial pain is aggravated by use of the involved muscle(s), psychological stressors, anxiety, cold and postural imbalance. Radiation from a trigger point may be described in terms of paresthesiae and thus mimic the symptoms of a cervical or lumbar radiculopathy. Muscle weakness secondary to disuse may present with symptoms weakness, poor coordination, reduced work tolerance, fatigue and sleep disturbance. Patients with myofascial pain involving the neck and face muscles may experience symptoms of dizziness, tinnitus and poor balance.
The characteristic features of a myofascial trigger point:
1. Focal point of tenderness to palpation of the involved muscle
2. Reproduction of pain complaint by trigger point palpation (about 3 kg pressure)
3. Palpation reveals an induration of the adjacent muscle (the “taught band”)
4. Restricted range of movement in the involved muscle
5. Often pseudo-weakness of the involved muscle (no atrophy)
6. Often referred pain on continued (~5 secs) pressure over trigger point.

Common Symptoms of Myofascial Pain
A myofascial pain syndrome may be due to just one trigger point, but more commonly there are several trigger points responsible for any given regional pain problem. It is not uncommon for the problem to be initiated with a single trigger point with the subsequent development of satellite trigger points that evolve over time due to the mechanical imbalance resulting from reduced range of movement and pseudo-weakness. The persistence of a trigger point may lead to neuroplastic changes at the level of the dorsal horn which results in amplification of the pain sensation (i.e. central sensitization) with a tendency to spread beyond its original boundaries (i.e. expansion of receptive fields) (13). In some instances segmental central sensitization leads to the phenomena of mirror image pain (i.e. pain on the opposite side of the body in the same segmental distribution) and in other instances a progressive spread of segmental central sensitization gives rise to the widespread pain that characterizes fibromyalgia (14).
Low back pain
Acute low back pain has many causes. Some are potentially serious, such as cancer metastases, osteomyelitis, massive disk herniations (e.g. cauda equina syndrome), vertebral fractures, pancreatic cancer and aortic aneurysms. However the commonest cause of acute back pain is so-called lumbosacral strain. In 95% of cases this resolves within three months. In those cases that do not resolve the development of a chronic low back pain syndrome is usually accompanied by the finding of active myofascial trigger points. Simons of describes 15 torso and pelvic muscles which may be involved in low back pain (10). The most commonly involve muscle group is the quadratus lumborum; pain emanating from trigger points in these muscles is felt fin the low back with occasional radiation in a sciatic distribution or into the testicles. Trigger points involving the iliopsoas are also a common cause of chronic low back pain. The typical distribution of iliopsoas pain is a vertical band in the low back region and the upper portion of the anterior thigh. Trigger points at the origin of the gluteus medius from the iliac crest are common cause for low back pain in the sacral and buttock with a referral pattern to the outer hip region.
Neck and shoulder pain
Latent trigger points are universal finding in many of the muscles of the posterior neck and upper back. Active trigger points commonly involve the upper portion of the trapezius and levator scapula. Upper trapezius trigger points referred pain to the back of the neck and not uncommonly to the angle of jaw. Levator scapula trigger points cause pain at the angle of the neck and shoulder; this pain is often described as lancinating, especially on active use of this muscle. As many of the muscles in this area have an important postural function they are commonly activated in office workers and developmental problems causing spinal malalignment (e.g. short leg syndrome, hemipelvis and scoliosis). As the upper trapezius and levator scapulae act synergistically with several other muscles in elevation and fixation of the scapula it is common for a single trigger point in this region to initiating a spread of satellite trigger points through adjacent muscles which are part of the same functional unit.
Hip pain
Pain arising from disorders of the hip joint is felt in the groin and the lower medial aspect of the anterior thigh. This distribution is uncommon in myofascial pain syndromes except for iliopsoas pain. The great majority of patients complain of hip pain in fact localize their pain to the outer aspect of the hip. In some patients this is due to a trochanteric bursitis, but in the majority of cases it is related to myofascial trigger points in the adjacent muscles. By far the commonest trigger points giving rise to outer hip pain are those in the attachments of the gluteus medius and minimus muscles into the greater trochanter.
Pelvic pain
The pelvic floor musculature is a common sight for myofascial trigger points. There is increasing recognition by gynecologists and urologists that pain syndromes described in terms of prostatitis, coccydnia, vulvodynia and endometriosis are often accompanied by active myofascial trigger points. One of the most commonly involved intrapelvic muscles is the levator ani; its pain distribution is central low buttock.
Active myofascial trigger points in the muscles of the shoulder neck and face are a common source of headaches (15). In many instances the headache has the features of so-called tension headache, but there is increasing acceptance that myofascial trigger points may initiate classical migraine headaches or be part of a mixed tension/migraine headache complex. For instance sterno-cleido mastoid trigger points refer pain to the anterior face and supraorbital area. Upper trapezius trigger points refer pain to the vertex forehead and temple. Trigger points in the deep cervical muscles of the neck may cause post occipital and retro-orbital pain.
Jaw pain
There is a complex interrelationship between temporomandibular joint dysfunction and myofascial trigger points (3) Common trigger points involved in jaw pain syndromes are the massetters, pterygoids, upper trapezius and upper sterno-cleido mastoid.
Upper Limb pain
The muscles attached to the scapula are common sites for trigger points that can cause upper limb pain (16). These included the subscapularis, infraspinatus, teres major and serratus anterior. It is not uncommon for trigger points in these locations to refer pain two the wrist hand and fingers. Extension flexion injuries to the neck often activate a trigger point in the pectoralis minor with a radiating pain or down the ulnar side of the arm and into the little finger. Myofascial pain syndromes of the upper limb are often misdiagnosed as frozen shoulder, cervical radiculopathy or thoracic outlet syndrome (10).
Lower limb pain
Trigger points in the tensor fascia lata and ilio tibial band may be responsible for lateral thigh pain and lateral knee pain respectively. Anterior knee pain may result from trigger points in various components of the quadriceps musculature. Posterior knee pain can result from trigger points in the hamstring muscles and popliteus. Trigger points in the anterior tibialis and the peroneus longus muscles may cause pain in the anterior leg and lateral ankle respectively. Myofascial pain syndromes involving these muscles are often associated with ankle injuries or an excessively pronated foot. Sciatica pain may be mimicked by a trigger point in the posterior portion of the gluteus minimus muscle.
Chest and abdominal pain
Disorders affecting intrathoracic and intra-abdominal organs are some of the commonest problems encountered in internal medicine. For instance, anterior chest pain is a frequent cause for the emergency room admissions, but in the majority of patients a myocardial infarction is not found. In some cases the chest pain is caused by trigger points in the anterior chest wall muscles (17). Pectoralis major trigger points cause ipsilateral anterior chest pain with radiation down the ulnar side of the arm – thus mimicking cardiac ischemic pain. A trigger point in the sternalis muscle typically causes a deep substernal aching sensation. Trigger points at the upper and lower insertions of the rectus abdominus muscles may mimic the discomfort of gall bladder and bladder infections respectively. It is important to note that myofascial trigger points may accompany disorders of intrathoracic and intra-abdominal viscera, and thus a diagnosis of an isolated myofascial cause for symptoms should never be made without an appropriate workup.
The precise basis for the trigger point phenomena is still not fully understood. There is a general agreement that electromyographic recordings from trigger points show low voltage spontaneous activity resembling endplate spike potentials (18). Simons envisions a myofascial trigger point to be “a cluster of numerous microscopic loci if intense abnormality that are scattered throughout the tender nodule” (10). It is thought that these loci result from a focal energy crisis (from injury or repetitive use) that results in contraction of focal sarcomeric units due to calcium release from the sarcoplasmic reticulum. Factors commonly cited as predisposing to trigger point formation include deconditioning, poor posture, repetitive mechanical stress, mechanical imbalance (e.g. leg length inequality), joint disorders, non-restorative sleep and vitamin deficiencies.
Here is a cartoon of a trigger point complex seen in a longitudinal section of muscle. The top component represents a muscle with a taut band. The middle component represents a magnified view of the taut band containing an active trigger point focus. The lower component represents further magnification of the taut band and trigger point focus showing contraction knots (contracted sarcomere units). It is envisaged that these contraction knots are responsible for the nodularity of the taut band.

Uncomplicated myofascial pain syndromes usually resolve with appropriate correction of predisposing factors and myofascial treatment (12). If the symptoms are persistent, due to ineffective management, the development of segmental central sensitization may lead to a stubbornly recalcitrant pain disorder. In some such cases, the spread of central sensitization leads to the widespread pain syndrome of fibromyalgia

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