Pathogenesis of papular urticaria.

The presence of immunoglobulin and complement deposits in the skin of three patients with papular urticaria suggests that these lesions may be due to a cutaneous vasculitis. These deposits were most frequently found in biopsy specimens taken from lesions within 24 hours of their development. The presence of granular deposits of Clq, C3, and IgM in the walls of the superficial dermal blood vessels suggests that immune complexes (IgM aggregates) may be primarily involved in the pathogenesis of these lesions, with complement activation initiated by Clq through the classical pathway.