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
**Core Concept**
The sudden onset of fever, abdominal pain, hematuria, and palpable purpuric skin lesions in a child suggests a systemic vasculitis, specifically a form of Henoch-Schönlein purpura (HSP), which is characterized by the deposition of IgA immune complexes in small blood vessels.
**Why the Correct Answer is Right**
HSP is a form of vasculitis that primarily affects small vessels, including capillaries, venules, and arterioles. The deposition of IgA immune complexes leads to inflammation and damage to the blood vessel walls, resulting in the characteristic purpuric skin lesions, abdominal pain, and glomerulonephritis. The involvement of the kidneys (hematuria and proteinuria) is a common complication of HSP, which can lead to long-term renal damage if not promptly treated.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not match the clinical presentation of HSP. Henoch-Schönlein purpura is a distinct clinical entity characterized by the specific combination of symptoms and findings mentioned in the question.
**Option B:** This option is incorrect as it refers to a different condition. Kawasaki disease is a medium vessel vasculitis that primarily affects children, but it does not typically present with purpura or abdominal pain.
**Option C:** This option is incorrect as it is a more severe and systemic form of vasculitis. Polyarteritis nodosa (PAN) is a medium and large vessel vasculitis that can involve multiple organs, but it does not typically present with the characteristic purpuric skin lesions of HSP.
**Option D:** This option is incorrect as it does not match the clinical presentation of HSP. Idiopathic thrombocytopenic purpura (ITP) is a bleeding disorder characterized by low platelet count, which can lead to petechiae and purpura, but it does not typically present with abdominal pain or hematuria.
**Clinical Pearl / High-Yield Fact**
The classic "tetrad" of HSP includes purpura, abdominal pain, arthritis, and renal involvement. Remember that HSP is a form of IgA vasculitis, and prompt recognition and treatment are essential to prevent long-term renal damage.
**Correct Answer:** C.