Review Question - QID 212437

A 27-year-old man arrives to the urgent care clinic complaining of a genital lesion. He noticed the lesion 3 days ago. It began as a small, firm, red papule that subsequently ulcerated. He denies pain, pruritis, or drainage from the site. He denies dysuria, hematuria, or penile discharge. His medical history is significant for attention deficit hyperactivity disorder. He takes methylphenidate. He recently became single following a long-term relationship and states that he is sexually active with “multiple women.” Physical examination reveals enlarged left-sided inguinal lymph nodes and an ulcerated lesion on the shaft of the patient's penis, as shown in Figure A. Which of the following tests is most likely to be positive for the patient's condition?