The most common and well-known entity in this category is Henoch-Schonlein (H-S) purpura. The primary abnormality is necrotizing inflammation of small venules, characterized by infiltration of the vessel wall by segmented neutrophils accompanied by destruction of some neutrophils with release of nuclear fragments (“leukocytoclastic vasculitis”). Immunohistologic methods can demonstrate IgA deposition in the vessel wall due to presence of IgA immune complexes. Overall, H-S purpura demonstrates purpura in over 90% of cases, arthralgias or arthritis in multiple joints in 80%-90% of cases, and gastrointestinal symptoms in about 70% of cases. Schonlein’s purpura features flat or nodular purpuric skin lesions, usually small but of varying size, most often on the lower extremities but which may occur elsewhere. There is no GI involvement. Henoch’s purpura features involvement of and bleeding into the GI tract without emphasis on skin manifestations. Renal involvement with hematuria may occur in either entity in 10%-40% of cases. The syndrome may follow an upper respiratory tract infection or may be due to a drug hypersensitivity reaction and may include systemic symptoms such as malaise, myalgia, and arthralgias. Platelet counts and other coagulation tests usually are normal, except for the tourniquet test, results of which are frequently abnormal. Diagnosis is usually made through biopsy of an area that is abnormal visually or clinically.