Myofascial Pain Syndome
About 23 million persons, or 10 percent of the U.S. population, have one or more chronic disorders of the musculoskeletal system. Musculoskeletal disorders are the main cause of disability in the working-age population and are among the leading causes of disability in other age groups. Myofascial pain syndrome is a common painful muscle disorder caused by myofascial trigger points. This must be differentiated from fibromyalgia syndrome, which involves multiple tender spots or tender points. These pain syndromes are often concomitant and may interact with one another.
Trigger points are discrete, focal, hyperirritable spots located in a taut band of skeletal muscle. The spots are painful on compression and can produce referred pain, referred tenderness, motor dysfunction, and autonomic phenomena.
Trigger points are classified as being active or latent, depending on their clinical characteristics. An active trigger point causes pain at rest. It is tender to palpation with a referred pain pattern that is similar to the patient's pain complaint. This referred pain is felt not at the site of the trigger-point origin, but remote from it. The pain is often described as spreading or radiating. Referred pain is an important characteristic of a trigger point. It differentiates a trigger point from a tender point, which is associated with pain at the site of palpation only (Table 1).
A latent trigger point does not cause spontaneous pain, but may restrict movement or cause muscle weakness. The patient presenting with muscle restrictions or weakness may become aware of pain originating from a latent trigger point only when pressure is applied directly over the point.
Moreover, when firm pressure is applied over the trigger point in a snapping fashion perpendicular to the muscle, a "local twitch response" is often elicited. A local twitch response is defined as a transient visible or palpable contraction or dimpling of the muscle and skin as the tense muscle fibers (taut band) of the trigger point contract when pressure is applied. This response is elicited by a sudden change of pressure on the trigger point by needle penetration into the trigger point or by transverse snapping palpation of the trigger point across the direction of the taut band of muscle fibers. Thus, a classic trigger point is defined as the presence of discrete focal tenderness located in a palpable taut band of skeletal muscle, which produces both referred regional pain (zone of reference) and a local twitch response. Trigger points help define myofascial pain syndromes.
Tender points, by comparison, are associated with pain at the site of palpation only, are not associated with referred pain, and occur in the insertion zone of muscles, not in taut bands in the muscle belly.8 Patients with fibromyalgia have tender points by definition. Concomitantly, patients may also have trigger points with myofascial pain syndrome. Thus, these two pain syndromes may overlap in symptoms and be difficult to differentiate without a thorough examination by a skilled physician.
There are several proposed histopathologic mechanisms to account for the development of trigger points and subsequent pain patterns, but scientific evidence is lacking. Many researchers agree that acute trauma or repetitive microtrauma may lead to the development of a trigger point. Lack of exercise, exposure to toxic molds, vitamin deficiencies and sleep disturbances may all predispose to the development of microtrauma. Occupational or recreational activities that produce repetitive stress on a specific muscle or muscle group commonly cause chronic stress in muscle fibers, leading to trigger points. Examples of predisposing activities include holding a telephone receiver between the ear and shoulder to free arms; prolonged bending over a table; sitting in chairs with poor back support, improper height of arm rests or none at all; and moving boxes using improper body mechanics.
Acute sports injuries caused by acute sprain or repetitive stress (e.g., pitcher's or tennis elbow, golf shoulder), surgical scars, and tissues under tension frequently found after spinal surgery and hip replacement may also predispose a patient to the development of trigger points.
Patients who have trigger points often report regional, persistent pain that usually results in a decreased range of motion of the muscle in question. Often, the muscles used to maintain body posture are affected, namely the muscles in the neck, shoulders, and pelvic girdle, including the upper trapezius, scalene, sternocleidomastoid, levator scapulae, and quadratus lumborum. Although the pain is usually related to muscle activity, it may be constant. It is reproducible and does not follow a dermatomal or nerve root distribution. Patients report few systemic symptoms, and associated signs such as joint swelling and neurologic deficits are generally absent on physical examination.
In the head and neck region, myofascial pain syndrome with trigger points can manifest as tension headache, tinnitus, temporomandibular joint pain, eye symptoms, and torticollis. Upper limb pain is often referred and pain in the shoulders may resemble visceral pain or mimic tendonitis and bursitis. In the lower extremities, trigger points may involve pain in the quadriceps and calf muscles and may lead to a limited range of motion in the knee and ankle. Trigger-point hypersensitivity in the gluteus maximus and gluteus medius often produces intense pain in the low back region.
Palpation of a hypersensitive bundle or nodule of muscle fiber of harder than normal consistency is the physical finding most often associated with a trigger point.Localization of a trigger point is based on the physician's sense of feel, assisted by patient expressions of pain and by visual and palpable observations of local twitch response. This palpation will elicit pain over the palpated muscle and/or cause radiation of pain toward the zone of reference in addition to a twitch response.
No laboratory test or imaging technique has been established for diagnosing trigger points.However, the use of ultrasonography, electromyography, thermography, and muscle biopsy has been studied.