Allergic vasculitis: most common of the necrotizing vasculitides

Allergic vasculitis presents with purpuric lesions that are distinguishable by their palpability and by their distribution primarily on the lower extremities. The disease can affect any organ system but most often involves the kidneys, joints, gastrointestinal tract, lungs, or nervous system. Histopathologic examination shows characteristic destruction of the vessel wall by polymorphonuclear leukocytes. Numerous etiologic agents have been implicated, but streptococcal infection and drug ingestion are the most common. Presumptive evidence suggests that the disease is due to immune complexes. The workup is aimed at establishing the cause and extent of systemic involvement, and treatment is tailored accordingly.