How can the pain of Fibromyalgia be distinguished from the pain of widespread arthritis? Why is this important?
Patients with FM generally have diffuse deep aching pain that may be perceived to originate within joints, muscles, or both; thus, it may be confused with a diffuse arthritis syndrome such as RA or AS. Pain involving the axial skeleton is universally present in FM, with patients experiencing lower back, cervical spine, and/or thoracic spine pain. Patients with FM also commonly experience bilateral pain in the upper and lower extremities. True arthritis can be excluded by the physical examination. The joint exam in primary FM reveals absence of effusion, synovial proliferation, deformity, and warmth. In addition, the presence of tenderness on exam consistently outside of anatomic joint locations is helpful in distinguishing this disorder from a diffuse arthritis syndrome. Finally, laboratory and radiographic findings are normal in primary FM.
FM may occur alone (primary FM) or may coexist with numerous other medical syndromes, including arthritis. Up to 20% of patients with RA and SLE can have secondary FM. Therefore, the presence of an arthritis syndrome does not exclude the presence of coexistent FM, and vice-versa. In these cases, the diagnosis of superimposed FM may be considered if subjective pain and constitutional symptoms exceed that expected for the degree of objective arthritis as determined by physical examination, radiographs, and laboratory tests. The presence of diffuse tender points may also suggest the diagnosis of coexistent FM.
The importance of recognizing the existence of secondary FM in patients with an underlying inflammatory arthritis is to avoid unnecessary escalation of immunosuppressive therapy. The evaluation of patients with RA or SLE who have secondary FM may be challenging, as these patients may have tenderness with joint palpation due to central sensitization and generalized pain magnification rather than active inflammatory disease. This may fool the physician, prompting an inappropriate escalation in therapy. Therefore in patients with an inflammatory arthritis who have secondary FM, the presence of swollen joints, limitation of range of motion, and abnormal inflammatory markers may be more important than the presence of tender joints on exam. Similarly, evidence has shown that several disease activity measurements can be adversely influenced by conditions such as FM, osteoarthritis, and depression and should be interpreted with caution in these settings.