PLE-4905

A previously healthy 10-year-old boy is brought to the physician because of a rash over his arms and legs for 7 days. His blood pressure is elevated. On physical examination, a yellow, crusted, excoriated rash over the upper and lower extremities is seen. Urinalysis reveals 100 RBC/hpf and 5-10 WBC/hpf. Which of the following is the most likely diagnosis?