In Brief: Musculoskeletal complaints are among the leading reasons for visits to physicians, and about one third of these patients meet diagnostic criteria for myofascial pain syndrome (MPS). Although MPS was identified more than a century ago, debate over its existence as a separate clinical entity continues. Physicians who learn to identify characteristic symptoms can differentiate MPS from fibromyalgia and provide effective treatment. Key to treatment is identification of trigger points that when stimulated produce patterns of pain throughout a limb or region. Treatment modalities for MPS include trigger point injection, shiatsu, and the spray and stretch technique. Prognosis for MPS is better than that for fibromyalgia, and treatment usually follows an individualized regimen.

The musculoskeletal system comprises more than 400 individual muscles and is the largest organ system by weight in the human body.¹ A recent study² identified musculoskeletal complaints as one of the leading causes for patients to visit a primary care provider. As many as one third of these patients had symptoms that met the diagnostic criteria for myofascial pain syndrome (MPS).¹

Although MPS has been described variously in the literature since 1843,³ the debate over its existence continues. Whether one takes the position that it is a subset of fibromyalgia or a separate entity, treatment for MPS differs from that of fibromyalgia, as does its prognosis. Patients who have MPS often have regional pain symptoms after a relatively minor trauma or muscle overuse.

Describing and Distinguishing the Pathology

Simons et al¹ have defined regional MPS as a condition in which the patient has "hyperirritable spots" or "trigger points" within taut bands of skeletal muscle or fascia that are painful on compression and can give rise to characteristic referred pain, tenderness, and autonomic nervous system symptoms. Pain from MPS can be described as deep and achy, and it is occasionally accompanied by a sensation of burning or stinging. Patients may also report restricted range of motion in the area affected. MPS is limited to one area or quadrant of the body.¹

Differentiating the disorders. In 1990, the American College of Rheumatology developed criteria for the diagnosis of fibromyalgia,⁴ a condition that can sometimes be confused with MPS. MPS can be distinguished from fibromyalgia in a number of ways (table 1). Fibromyalgia is a disorder of sleep that affects areas throughout the body,⁴ while MPS is a disorder of muscle physiology, affecting only one region or extremity. In addition, MPS has a much better prognosis than fibromyalgia.^5,6

Some clinicians are skeptical that MPS is a distinct disorder and believe that the condition is a subset of fibromyalgia.⁷ The early literature on these conditions uses the two diagnoses interchangeably. Much of the controversy centers around differentiating the "tender points" found in patients with fibromyalgia and the "trigger points" found in patients with MPS. The trigger point may be associated with a local "jump response" or "jump sign." Thus, when physicians palpate the affected muscle, they feel a "knotted" or "doughy" area, and the patient may instinctively recoil or jump when the area is identified. A tender point associated with fibromyalgia may not be detected when palpated and may represent only an area of maximum tenderness within a sore muscle. Tender points are not associated with referred pain patterns, jump signs, or the motor endplates of the muscle-nerve interface.

One study⁷ employed clinical experts to perform tender point examinations on three groups of patients. A small number of patients were prediagnosed with either fibromyalgia or MPS. These patients were compared with 80 "healthy" patients. The experts found taut bands of muscle and muscle twitches in both healthy controls and in patients with either of the conditions. A liberal definition of "trigger points" by these investigators produced overlap between the fibromyalgia group and the MPS group, and local areas of tenderness or "tender spots" were found in both groups.⁷ A second study⁸ of similar design found that dolorimetry and palpation were very reliable in discriminating between control patients and those with MPS or fibromyalgia.

Muscle Basics, Trigger Points, and Pain Patterns

A review of structural and physiologic principles of muscle contraction helps address syndrome etiology and provides tips on trigger point identification.

Muscle structure and contraction. Skeletal muscle is an assembly of fascicles, each of which is a bundle of roughly 100 muscle fibers. Each muscle fiber or cell encloses approximately 1,000 to 2,000 myofibrils. Myofibrils consist of chains of sarcomeres connected serially, end-to-end. Individual sarcomeres are basic contractile units of skeletal muscle connected by z-lines, often described as "links in a chain" when visualized under the microscope. Each sarcomere is composed of actin and myosin molecules that form cross-bridges in the presence of ionized calcium.

When adenosine triphosphate (ATP) is bound to myosin, the actin-myosin cross-bridge remains relaxed (not attached). Hydrolysis of ATP into adenosine diphosphate (ADP) results in the interaction or crossbridging of the actin and myosin proteins. ADP then dissociates from the myosin, causing it to bend or "cock," thus pulling on the actin and shortening the sarcomere. Reattachment of another ATP releases the cross-bridge and uncocks the myosin, allowing the process to start over. As these cycles are repeated, the muscle contracts. When calcium is removed, the contraction is terminated. Without additional ATP input, the cross-bridges remain attached, myosin staythin the muscles affects the pain pathway.

In MPS, palpating the muscle is painful. The pain is relieved by Such stretching is exquisitely painful and requires temporarily blocking pain receptors while the involved muscle is stretched. This phenomenon is the reason that spray and stretch, local injection, and acupressure—all of which inhibit pain and motor reflex—are employed in treatment as the muscle is stretched to length.

Although many theories responsible for MPS have been postulated,^5,11 no clear causal factors have been identified. Clinical studies have shown some association between MPS and prolonged static postures, lack of exercise, sleep disturbance, and emotional stress.⁵ With minimal training, clinicians can identify this syndrome based solely on history and physical examination findings.

Identifying trigger points. The recommended criteria for identifying trigger points consist of essential criteria and confirmatory observations (table 2).¹ Using pain diagrams, examiners can compare patient trigger points identified with those known from published drawings (figure 1).^5,10,12,13