What is your diagnosis?

A 2-year-old otherwise healthy male patient presents with a new "bumpy" rash that has been present for 1 week. For the prior 2 weeks, he had a red rash on his right anterior thigh, which was attributed to an irritant dermatitis and improved with triamcinolone 0.1% ointment. His mother reports that his new rash is distinct from this prior rash. He denies pruritus and scale. His mother reports that, prior to the onset of his new rash, he had a low grade fever and one episode of vomiting. He was given a single dose of ibuprofen and then went to sleep. The next morning, she reports he woke up with the new rash, as well as white exudate in his throat. He saw his primary physician, at which time he tested negative for streptococcal antigens. His fever and vomiting was limited to the 1-day episode, but the rash persisted.

On physical exam, he is noted to have shotty feel similar to buckshot or pelletscervical lymphadenopathy and generalized innumerable skin-to-white papules, some of which are flat; the papules are worse on the extensor aspects of the extremities and less prominent on his chest and face. He also has a 5-cm erythematous round patch on his right anterior thigh, minimal erythema around the rectum, and positive dermatographism test at his thighs.