Review Question - QID 212552

A 34-year-old woman presents to your clinic with a 6-month history of pain in her hands. The pain is worse in the morning but is present throughout the day despite her use of ibuprofen. Additionally, her left 4th finger recently began to swell and is particularly painful. She has also begun to notice changes in her nails, which have become brittle. Prior to the onset of symptoms, she made multiple visits to the clinic with complaints of pain in her lower back and ankles that was eventually well controlled with ibuprofen. Her temperature is 99.5°F (37.5°C), pressure is 138/88 mmHg, pulse is 78/min, and respirations are 18/min. Inspection of the hands demonstrates the physical examination findings present in Figure A. Additionally, a rash on the right elbow is identified and pictured in Figure B. The distal interphalangeal joints of the left hand are tender to palpation, as is the second distal interphalangeal joint of the right hand. The Achilles tendons are tender bilaterally, and ultrasonography is consistent with mild Achilles tendonitis bilaterally. Testing for HLA-B27 is positive. Which of the following is the most likely diagnosis?