A 60-year-old man had joint pain, swelling, and the inability to flex his fifth finger for several years. The swelling had appeared gradually after episodes of acute pain in that finger. He had chronic kidney disease (creatinine level of 5.3 mg per dL and poorly controlled diabetes mellitus (fasting glucose level of 172 mg per dL). On examination, there was swelling of the fifth proximal interphalangeal joint with yellow discoloration under the skin (Figure 1). There was no erythema or warmth. A radiograph showed a 3-cm area of swelling at the center of the joint with advanced bony erosion (Figure 2). What is the most likely diagnosis?
