A 32-year-old woman undergoes a new patient evaluation. She was diagnosed with systemic lupus erythematosus 10 years ago; manifestations have included arthritis, pericarditis, leukopenia, and rash. She reports increasing difficulty using her hands due to joint deformities. Medications are hydroxychloroquine and prednisone.

On physical examination, temperature is 36.8 °C (98.2 °F), blood pressure is 130/85 mm Hg, pulse rate is 80/min, and respiration rate is 16/min. BMI is 24. Examination of the hands reveals subluxation and ulnar deviation of the metacarpophalangeal joints on both hands, swan neck deformity of fingers on both hands, flexion and subluxation of the metacarpophalangeal joint of both thumbs, and hallux valgus of the first metatarsophalangeal joints bilaterally.

Hand radiographs demonstrate no deformities or evidence of erosions.

Which of the following is the most likely diagnosis?