What additional studies are indicated in selected patients to evaluate chronic monoarticular arthritis?
• Erythrocyte sedimentation rate or C-reactive protein: Although results are often nonspecific, significant elevation may suggest an inflammatory process.
• Radiograph of sacroiliac joints: This may demonstrate asymptomatic sacroiliitis in young patients presenting with chronic monoarticular arthritis as an initial manifestation of axial spondyloarthritis.
• Chest radiograph: To detect evidence of prior mycobacterial disease or pulmonary sarcoidosis.
• Skin test reaction to tuberculin or interferon-gamma release assay: A negative test is useful in excluding mycobacterial infection.
• Serologic tests for Lyme disease ( Borrelia burgdorferi ), rheumatoid factor, anti-cyclic citrullinated peptide antibody, ANA, and human leukocyte antigen B27.
These additional studies are most helpful in suspected inflammatory etiologies of chronic monoarticular arthritis, as well as those patients without a definitive etiology after initial joint aspiration and radiograph of the affected joint.