Classification of urticaria and the reactive inflammatory vascular dermatoses.

The common feature of all the conditions discussed in this article is that they are inflammatory vascular dermatoses that may occur as reactive processes in association with other diseases. The histopathologic characteristics of the lesions range from mild, perivascular dermal infiltration with inflammatory cells and vasodilation to various degrees of vessel damage (endothelial swelling to fibrinoid necrosis). The vessel damage is reflected in varying degrees of secondary changes including extravasation of edema fluid, extravasation of erythrocytes, epidermal necrosis, separation of the dermal-epidermal junction zone, and widespread tissue necrosis. The etiology of most of these conditions is still unknown, although strong evidence indicates that type III (circulating immune-complex-mediated) pathogenesis may be responsible for necrotizing venulitis (leukocytoclastic vasculitis) and that a type I (IgE-mediated) pathogenesis may be involved in some types of urticaria. For many of the reactions described, the patients have serum sickness-like systemic signs and symptoms in addition to cutaneous lesions, and a circulating immune-complex-mediated pathogenesis has been considered. Future investigations must address the types of antigens and antibodies present in the circulating immune complexes, the detection of specific antigen in cutaneous blood vessels, the reproduction of lesions in experimental animals, and the mechanisms responsible for the spectrum of clinicopathologic lesions produced, with special attention to the possibility that vessel damage results from circulating immune complex-induced lymphocytic rather than only leukocytoclastic vasculitis.