Cutaneous clinicopathologic correlation of allergic granulomatosis

Allergic granulomatosis is a distinct clinical syndrome occurring in adults with asthma, eosinophilia, and multisystem vasculitis. Atopy and drug sensitivity are other important features. The skin reactions are most commonly nodular and inflammatory lesions. A unique feature is the deep papulonodules, which may occur singly on the scalp or symmetrically on the extremities. Cutaneous findings may range from purpura to urticaria and ulceration. The most common histologic finding is the extravascular granuloma; however, necrotizing vasculitis of small vessels is seen, as well as periarteritis nodosa involving larger vessels of the skin. This varied histologic and clinical spectrum seen in patients with systemic allergic granulomatosis is a reflection of a unique host response to multiple antigens. The cutaneous findings imply that allergic granulomatosis probably represents a unique host response to the same causative and pathogenetic factors as are usually found in periarteritis nodosa and necrotizing vasculitis.