The spectrum of systemic vasculitis: a classification to aid diagnosis.

Determining the cause of systemic vasculitis can be facilitated by a clinicopathologic classification of the syndrome. The considerations in differential diagnosis include periarteritis nodosa, leukocytoclastic angiitis (hypersensitivity angiitis, Schonlein-Henoch purpura, other disease-associated vasculitis), Wegener's granulomatosis, allergic granulomatosis (granulomatous angiitis), and giant cell arteritis.