A 3-Week-Old With an Isolated "Blueberry Muffin" Rash

A 3-week-old boy, former 39-week term infant, presented to the emergency department with a rash. One week before presentation, he developed dark, purple papules on his forehead, which then spread to the abdomen and inguinal regions. Throughout this time, he was eating well, gaining weight, developing appropriately, and was afebrile without cough, congestion, or rhinorrhea. On presentation, the patient was well appearing with normal vital signs. His weight was 4.83 kg (86th percentile for age), his length was 56 cm (47th percentile for age), and his head circumference was 37 cm (62nd percentile for age). On skin examination, there were scattered purpuric papules and macules on the scalp, forehead, trunk, abdomen, and inguinal region. Initial laboratory studies were remarkable only for mild anemia. Our expert panel examines the case, offers a differential for a child with a "blueberry muffin" rash, and makes diagnostic considerations.