Which physical finding differentiates rheumatoid arthritis from osteoarthritis on exam?

• A. Symmetric joint swelling including MCP and PIP joints with possible ulnar deviation
• B. Asymmetric involvement of large joints
• C. Isolated knee effusion
• D. Localized swelling of a single DIP joint

Answer: (A)

Pattern of joint involvement differentiates the two. Rheumatoid arthritis typically shows symmetric swelling of the small hand joints, especially the metacarpophalangeal and proximal interphalangeal joints, and can progress to ulnar deviation from inflammatory damage. Osteoarthritis, by contrast, is usually asymmetric and more often affects larger weight-bearing joints; it commonly involves the DIP joints (Heberden nodes) or the PIP with different nodal changes, and may present with a knee effusion but not the same symmetric small-joint pattern. Therefore, symmetric swelling of MCP and PIP joints with possible ulnar deviation best differentiates RA from OA.