Histologic studies of chronic idiopathic urticaria.

Skin biopsy specimens were obtained from 43 consecutive patients with chronic idiopathic urticaria and from seven normal controls. Of 43 patients, 42 had a non-necrotizing perivascular infiltrate composed primarily of mononuclear cells. There was no evidence of damage to vessel walls, of nuclear debris, or of extravasation of red blood cells, and most cells were seen around vessels rather than within the vessel wall. One patient had vasculitis with a neutrophilic infiltrate, nuclear debris, and positive immunofluorescence. Quantitative cell counts revealed four times the number of mononuclear cells and 10 times the number of mast cells in urticaria biopsy sites vs normal skin. Thus chronic urticaria is characterized by an accumulation of mononuclear cells and mast cells with mast cell degranulation presumably associated with hive formation. In our series, the characteristic lesion is not vasculitic. The stimulus responsible for the infiltration of skin with these cells is unknown.