A 4-year-old boy is seen after he suddenly develops a fever, abdominal pain and tenderness, hematuria, and palpable purpuric skin lesions on his buttocks and the extensor surfaces of the arms and legs. The most likely diagnosis is

Henoch-Schonlein purpura- IgA immune complex disease, Involvement of small vessels (venules, capillaries, aerioles) with multiple lesions The disorder may involve only the skin, presenting as palpable purpura, or it may involve a variety of other sites, including the glomeruli, gastrointestinal tract, lungs, or brain. Thrombocytopenia is not seen in Henoch-Schonlein purpura (HSP)