A 23-year-old woman is evaluated for a 1-week history of fevers, malaise, aches of her elbows and left knee, and pain of her wrists, hands, and ankles that is worse with movement. She has noticed transient skin lesions resembling pustules. She reports no urinary symptoms or vaginal discharge. She has no history of illicit drug use; she drinks alcohol socially and is sexually active. She has not traveled recently. Her only medication is an oral contraceptive.
On physical examination, the patient appears uncomfortable. Temperature is 38.3 °C (100.9 °F), blood pressure is 115/75 mm Hg, pulse rate is 95/min, and respiration rate is 12/min. BMI is 23. Ulnar deviation of the wrists while holding the thumbs down elicits pain over the radial side of the wrists (positive Finkelstein test). There is generalized swelling of several fingers with tenderness to palpation diffusely. The left knee is warm, with a small effusion and pain with range of motion. The ankles have tenderness to palpation over the posterior aspects, with erythema along the Achilles tendons and pain with range of motion bilaterally. There are a few scattered vesiculopustular lesions over the palmar aspect of the hands and upper extremities.
Laboratory studies reveal a leukocyte count of 13,500/µL (13.5 × 109/L) and normal kidney and liver chemistries.
Which of the following is most likely to provide the diagnosis?