Henoch-Schönlein purpura: a diagnosis not to be forgotten.

Henoch-Schönlein purpura (HSP) is a systemic, generalized vasculitis of unknown etiology thought to be related to an IgA-mediated autoimmune phenomenon. Diagnosis is based on a constellation of physical findings that include the characteristic nonthrombocytopenic petechial or purpuric rash, migratory polyarthralgias, abdominal pain, and renal complications. We report the case of a 19-year-old man with a diagnosis of HSP who had severe abdominal pain and endoscopic documentation of duodenal involvement. Though not clear at presentation, the diagnosis became obvious when the characteristic rash emerged.