8-year-old son to his primary care physician for pain in his knees and ankles that have been present for the past three days. She also notes that he has had a rash since yesterday, but otherwise feels well. The patient has no chronic illnesses, but he was brought in three weeks ago for an upper respiratory infection. Exam is significant for pain elicited on passive movement of the ankles and knees. Additionally, the patient is found to have an erythematous, slightly raised, non-blanching, maculopapular rash over the legs, buttocks, and posterior portion of the elbows. CBC shows WBC 8.9, Hgb 12.5, Hct 36.1, and Plt 327. Urinalysis is unremarkable. IgA deposition noted on skin biopsy