Problem:
A 17-year-old boy is brought to the physician because of a 12-day history of increasing pain and swelling of his right knee. For the past 3 weeks, he has experienced episodes of pain when urinating. He had a tender swollen left ankle joint that resolved without treatment one week ago. His mother has rheumatoid arthritis. He is sexually active with 2 female partners and uses condoms inconsistently. He appears anxious. His temperature is 38°C (100.4°F), pulse is 68/min, and blood pressure is 100/80 mm Hg. Examination shows bilateral inflammation of the conjunctiva. The right knee is tender, erythematous, and swollen; range of motion is limited by pain. There is tenderness at the left Achilles tendon insertion site. Genital examination shows no abnormalities. Laboratory studies are shown below in the picture. An ELISA test for HIV is negative. Arthrocentesis is performed. Synovial fluid analysis shows a leukocyte count of 26,000/mm3 (70% neutrophils); a Gram stain shows no organisms. Which of the following is the most likely diagnosis? Captionless Image Septic arthritis Reactive arthritis Rheumatoid arthritis Syphilitic arthritis Lyme arthritis Reactive arthritis