A clinician narrows down a diagnosis of arthritis when there is DIP joint involvement only and the patient has iritis. Which arthritis is most likely?

• A. Ankylosing spondylitis
• B. Psoriatic arthritis
• C. Reactive arthritis
• D. Rheumatoid arthritis

Answer: (B)

Pattern recognition of inflammatory arthritis shows that involvement of the distal interphalangeal joints is a classic clue for psoriatic arthritis, especially when an inflammatory eye condition like iritis is present. Psoriatic arthritis is one of the seronegative spondyloarthropathies and often affects the DIP joints, can accompany dactylitis or enthesitis, and is associated with ocular inflammation such as iritis.

Rheumatoid arthritis typically targets the MCP and PIP joints and wrists, not the DIP, and while eye involvement can occur in inflammatory conditions, the DIP-predominant pattern with iritis aligns best with psoriatic arthritis. Ankylosing spondylitis centers on the spine and sacroiliac joints and commonly presents with back pain and reduced spinal mobility, though anterior uveitis can occur. Reactive arthritis can include conjunctivitis or uveitis but often features preceding infection and other mucocutaneous signs rather than DIP-only joint involvement.