Sudden, Painful Bumps on the Feet of a Child

An 8-year-old boy's mother takes him to the emergency department (ED) when he complains, suddenly, that the soles of his feet are extremely painful. He is an otherwise healthy active youngster. After laboratory tests are run, he is discharged from the ED with instructions to follow up with his primary care physician. See how the case unfolds, above. Do you recognize the lesions? What's in your differential diagnosis?