Fibromyalgia (FM) is a common cause of chronic widespread musculoskeletal pain, often accompanied by fatigue, cognitive disturbance, psychiatric symptoms, and multiple somatic symptoms. Despite the presence of soft tissue pain affecting the muscles, ligaments, and tendons, fibromyalgia itself is not associated with evidence of tissue inflammation, and a cardinal feature of FM is that the pain is not explained by another rheumatic or systemic disorder.
Explicit in the definition of FM is the exclusion of other conditions that can present with widespread pain. However, FM is often associated with other conditions that may cause musculoskeletal pain, disruption of sleep, or psychiatric symptoms; features of these conditions may also mimic FM, and the presence of such disorders should be considered in the diagnostic evaluation.
This topic will review the differential diagnosis of FM in adults. The clinical manifestations, diagnosis, and treatment of this condition in adults, as well as FM in children and adolescents, are discussed in detail elsewhere. (See "Clinical manifestations and diagnosis of fibromyalgia in adults" and "Approach to the patient with myalgia" and "Initial treatment of fibromyalgia in adults" and "Treatment of fibromyalgia in adults not responsive to initial therapies" and "Fibromyalgia in children and adolescents: Clinical manifestations and diagnosis" and "Fibromyalgia in children and adolescents: Treatment and prognosis".)
APPROACH TO THE DIFFERENTIAL DIAGNOSIS
The differential diagnosis of fibromyalgia (FM) is large, given the number of conditions that can present with signs or symptoms of FM, such as pain, fatigue and sleep disturbance, and symptoms of cognitive dysfunction and psychiatric disease . However, the diagnosis of FM and the exclusion of other alternative diagnoses included in the differential diagnosis can generally can be achieved based upon a thorough history and physical examination, and requires only limited laboratory testing (table 1 and algorithm 1). The diagnostic approach to FM is described in detail separately. (See "Clinical manifestations and diagnosis of fibromyalgia in adults", section on 'Diagnosis'.)
Fibromyalgia is diagnosed when characteristic features are present and other medical conditions have been excluded as the cause of the patient’s symptoms. The confidence that each clinician has in making this decision is related to their level of experience, particularly in evaluating rheumatic disorders. Features of each of the major conditions in the differential and potentially confounding factors to consider in the evaluation can be identified and are summarized in the table (table 2).