Which joint is classically affected by rheumatoid arthritis?

• A. DIP joints
• B. MCP joints
• C. PIP joints
• D. Tarsometatarsal joints

Answer: (B)

Rheumatoid arthritis classically targets synovial joints in a symmetric pattern, with the hands being a common early site. The metacarpophalangeal joints are the joints most characteristically involved, presenting with swelling, tenderness, and marked morning stiffness. This MCP predilection helps distinguish RA from other arthritides, since RA typically spares the distal interphalangeal joints, whereas osteoarthritis more often affects DIPs. The PIP joints can also be involved as the disease progresses, and other joints such as the wrists may become affected, but involvement of the metacarpophalangeal joints is the hallmark early target. Joints like the tarsometatarsal joints aren’t considered classically characteristic targets in early RA, though foot involvement can occur later.