Review Question - QID 214308

A 5-year-old boy presents to the emergency department for a rash. The child was previously healthy other than occasional colds. His rash started last night, and the child is now complaining of abdominal pain and diffuse joint pains. The patient's family was previously vegan and did not eat gluten; however, they recently began allowing their child to eat animal and gluten-containing products. They also noticed a small amount of dark blood in his stools. His temperature is 97.6°F (36.4°C), blood pressure is 94/54 mmHg, pulse is 99/min, respirations are 19/min, and oxygen saturation is 99% on room air. On physical exam, the child is uncomfortable appearing and is crying. Dermatologic exam reveals the finding in Figure A. The child begins screaming when he states he is having abdominal pain again. Which of the following is the most likely diagnosis?