Perivascular neutrophils, leukocytoclasis and fibrinoid degeneration involving the small dermal blood vessels with subsequent hemorrhage in a skin biopsy of a patient with HSP. Skin biopsy showing positive immunofluorescence of the small blood vessels for IgA. Henoch-Schonlein purpura (HSP) Acute immunoglobulin A (IgA)-mediated Generalized vasculitis involving the small vessels of the skin, the gastrointestinal (GI) tract, the kidneys, the joints, and, rarely, the lungs and the central nervous system (CNS). It is the most frequent vasculitis in childhood, the incidence decreasing with age. Subsequently, symptoms develop, of which the following are the most common: Rash, especially involving the legs; this is the hallmark of the disease Abdominal pain and vomiting Joint pain especially involving the knees and ankles Subcutaneous edema Scrotal edema Bloody stools