The prominent ulnar deviation of the hands and "swan neck" deformity of the fingers seen here is due to rheumatoid arthritis (RA). This autoimmune disease leads to synovial proliferation with inflammation and joint destruction, typically in a symmetrical pattern involving small joints of hands and feet, followed by wrists, ankles, elbows, and knees. Rheumatoid factor can be identified serologically in most, but not all, RA patients.

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