Fibromyalgia is a syndrome of unknown etiology characterized by chronic widespread joint and muscle pain. Fibromyalgia was previously referred to as fibrositis, a term coined by Sir William Gowers¹ in Europe referring to regional pain syndromes associated with profound fatigue and sleep disturbance. Fibromyalgia affects approximately 6 million people in the United States,² or up to 6% of the patients seen in general medical practices.³ Patients are usually diagnosed between the ages of 20 and 50 years, but the incidence rises with age so that, by age 80, approximately 8% of adults meet the classification criteria established by the American College of Rheumatology.⁴ The ratio of women to men with fibromyalgia varies between 9:1⁵ and 20:1.⁶ One prospective study⁷ showed that patients with fibromyalgia have approximately 10 outpatient clinic visits per year, 1 hospitalization per 3 years, and more than $2000 per year in medical costs. Another prospective study⁸ showed that total annual costs for fibromyalgia patients were close to $6000, compared with $2500 for typical patients. Six percent of these costs were attributable to fibromyalgia-specific claims. However, there may have been other hidden costs related to disability from fibromyalgia. This study also showed that, for every dollar spent on fibromyalgia-specific claims, the employer spent $57 to $143 on additional direct and indirect costs.

The American College of Rheumatology's criteria for fibromyalgia include diffuse soft tissue pain of at least 3 months' duration and pain on palpation in at least 11 of 18 paired tender points.⁴ These criteria are approximately 88% sensitive and 81% specific for the diagnosis of fibromyalgia. Symptoms are often exacerbated by exertion, stress, lack of sleep, and weather changes. In half of all patients, symptoms appear after a flu-like illness or after physical or emotional trauma.⁹ Approximately 30% of patients with fibromyalgia are diagnosed as having concurrent depression or anxiety disorders (Figure).¹⁰

DIAGNOSIS

The main challenge in evaluating patients with suspected fibromyalgia is that there is no gold standard test for diagnosis. It is primarily a diagnosis of exclusion, established only after other causes of joint or muscle pain are ruled out. The initial workup for patients who present with widespread musculoskeletal pain should include a complete blood count, erythrocyte sedimentation rate, liver function tests, hepatitis C antibody, calcium, and thyrotropin. Some experts recommend that patients with suspected fibromyalgia have a limited amount of testing before assigning the diagnosis. The clinician should keep in mind that an antinuclear antibody is often of low yield when other features of systemic lupus erythematosus or other antinuclear antibody–associated diseases are absent. In addition, false-positive results are common. In one series, 10% of patients with fibromyalgia had a positive antinuclear antibody.¹¹ Up to 30% of healthy women may test positive as well.¹² Similarly, imaging tests and neurophysiological studies are not recommended as initial screening tests.¹³

In most cases, the patient's history can distinguish fibromyalgia from other systemic illnesses. However, fibromyalgia often coexists with and has a tendency to mimic other illnesses. Estimates of its concomitance with systemic lupus erythematosus range as high as 45%. In one study¹⁴ of patients with lupus, 22% of the patients also met criteria for fibromyalgia. These patients had no difference in the measures of their lupus activity. However, they experienced greater disability associated with their illnesses. Twelve percent of patients with rheumatoid arthritis and 7% of patients with osteoarthritis meet the criteria for fibromyalgia.¹⁵ Twenty-five to 50% of patients with fibromyalgia have Raynaud phenomenon or have symptoms consistent with sicca syndrome.¹² Patients with fibromyalgia may initially be misdiagnosed as having seronegative spondyloarthropathies, such as ankylosing spondylitis, because they share the common complaints of neck, spine, and back pain. However, in the absence of other inflammatory disease, patients with fibromyalgia have normal erythrocyte sedimentation rates and normal findings on radiographic studies. In older adults, the syndrome is most commonly confused with polymyalgia rheumatica, which typically presents with persistent severe morning stiffness in the shoulders, pelvis, and torso. The erythrocyte sedimentation rate will be elevated in 80% to 90% of patients with polymyalgia rheumatica, and its symptoms respond to low-dose systemic corticosteroids. Fibromyalgia symptoms do not respond to corticosteroids,¹⁶ consistent with the noninflammatory nature of this disorder. However, patients with polymyalgia rheumatica who are tapered off corticosteroids too rapidly can occasionally develop symptoms similar to those of fibromyalgia. Most patients with chronic fatigue syndrome meet the criteria for fibromyalgia, and 70% of fibromyalgia patients meet criteria for chronic fatigue syndrome.¹⁷