Diagnostic Approach to Periarthritis

Laboratory Testing and Imaging

The European League Against Rheumatism recommends performing ESR and CRP at baseline when inflammatory periarthritis is suspected, as normal or mildly elevated markers suggest non-inflammatory causes, while significantly elevated markers indicate inflammatory arthritis or infection 1, 2, 3
The American College of Rheumatology suggests that autoantibody testing, including RF and ACPA, should be performed if rheumatoid arthritis is suspected, with negative tests not excluding RA progression 1, 3, 4

The American College of Radiology recommends that plain radiographs should be obtained in all patients with suspected periarthritis to identify calcific deposits, exclude fractures, and assess for erosive changes 1, 2, 4
The European Society of Musculoskeletal Radiology suggests that MRI is reserved for persistent symptoms unresponsive to treatment, diagnostic uncertainty, or when surgical planning is needed, and is not routinely recommended for initial diagnosis 5, 3

The Infectious Diseases Society of America recommends performing arthrocentesis urgently if septic arthritis cannot be excluded clinically, with synovial fluid analysis sent for cell count with differential, Gram stain, aerobic/anaerobic culture, and crystal analysis 6, 3, 4, 1
The American College of Rheumatology suggests that antimicrobials should be withheld for at least 2 weeks prior to aspiration to increase organism recovery, if the patient is medically stable 6