Complete and thorough management of the patient implies that fibromyalgia should be high in the differential when a patient has a complaint of widespread pain; however, other possible diagnoses should be excluded if any are clinically suspected. Rheumatic diseases such as systemic lupus erythematosus (SLE), rheumatoid arthritis,[10,11] and Sjögren syndrome (SS) also present with generalized fatigue, arthralgias, and myalgias. Additionally, the prevalence of these diseases is higher among patients with fibromyalgia than it is in the general population.[12,13] However, certain characteristics are more specific to these diseases and are not found in patients with fibromyalgia alone.
Serologic tests such as ANA and RF are not useful for differentiating these conditions from fibromyalgia. A prospective study conducted by Dinerman et al evaluated 118 patients with fibromyalgia and found that 14% had a positive ANA finding; however, 5%-10% of healthy women also have a positive ANA finding usually with low titers of the antibody. Similarly, RF is not specific to RA only and is positive in 5% of the general healthy population. Furthermore, a positive RF test result does not suggest the diagnosis of RA if the patient, like the one in this case, does not have signs and symptoms of RA; these primarily include painful, swollen joints or evidence of prior active arthritis, including limited range of motion or radiographic changes. More specific laboratory findings include positive anticyclic citrullinated peptide (anti-CCP) and anti–mutated citrullinated vimentin (anti-MCV) test results. These findings more strongly suggest RA or pre-RA; however, RA cannot be diagnosed in the absence of objective joint inflammation.
Patients with SLE may present with a facial butterfly rash; more specific serologic tests, such as anti-ds-DNA and anti-Sm antibodies, should be obtained if clinical suspicion for this disease is high.
Patients with SS present with complaints of xerophthalmia and xerostomia (dry mouth and eyes). In addition, serologic test results that are positive for antibodies to anti-SS-A and anti-SS-B are indicative of the disease.
Ankylosing spondylitis may present with fatigue and stiffness, but patients have limited axial spine mobility, as well as the characteristic "bamboo spine" and fused sacroiliac joints findings on radiography. The inflammatory changes that affect the axial spine can be diagnosed earlier with MRI.
Patients with myositis will present with myalgias, but their creatine kinase levels will be elevated. Additional considerations in the differential diagnosis of fibromyalgia that may need to be excluded with specific lab tests or imaging include multiple sclerosis, polymyalgia rheumatica, Lyme disease and other chronic infections (eg, mononucleosis, hepatitis), endocrine disorders (Cushing syndrome, hyperparathyroidism), and myofascial syndrome.
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