Painful Hand Swelling With Finger Contractures

A 56-year-old woman with no history of rheumatic disease or hand injury had swelling and tenderness of the bilateral wrists, metacarpophalangeal and proximal interphalangeal joints, nodular palmar tendon thickening, and flexion contractures of all fingers; results of serologic testing for autoimmune rheumatic diseases were negative. What is the diagnosis and what would you do next?