Review Question - QID 213512

A 34-year-old man presents to the clinic complaining of joint stiffness for the past 2 weeks. He reports that his bilateral distal interphalangeal joints are especially stiff when he wakes up but improve after 30-40 minutes. He denies any fever, trauma, weight loss, or gastrointestinal symptoms, but endorses an oral ulcer that he attributes to recent stress. His medical history is significant for a ventricular arrhythmia that he started taking procainamide for. A physical examination demonstrates skin findings shown in Figure A and mild swelling of the right index finger. Which of the following is the most specific finding you would expect in this patient?