This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Vasculitis, Subject name: Medicine
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 
Select and explain. 
A. Henoch-Schonlein purpura (HSP), B. Idiopathic (immune) thrombocytopenic purpura (ITP)., C. Kawasaki disease., D. Polyaeritis nodosa.
A: Henoch-Schonlein purpura (HSP)
Answer: A: Henoch-Schonlein purpura (HSP) 
Explanation: 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)