Cutaneous necrotizing venulitis.
The term vasculitis describes a variety of inflammatory changes in vessels. The most common type to affect the skin is a necrotizing venulitis associated with a neutrophilic polymorphonuclear leukocyte infiltrate. The most frequent presentation is palpable purpura on the lower extremities, but the lesions may  include urticaria and ulcers. A diagnosis of cutaneous necrotizing venulitis obliges the physician to search for the cause, associated diseases, and the extent of the vascular involvement. Antigens, either in circulating immune complexes or as haptens bound to vessel proteins, are presumed to trigger immmune responses. The differentiation of large from small vessel disease and the prediction of systemic involvement may be difficult in a specific patient. Treatment, other than removal of the antigen, is theoretic or anecdotal.
D006801:Humans; D018366:Vasculitis, Leukocytoclastic, Cutaneous / Q000145:classification / Q000175:diagnosis / Q000276:immunology / Q000628:therapy