Urticaria: the relationship of duration of lesion to pathogenesis.

It appears that when hives are fleeting, as is seen in physically induced hives, they are caused by a rapid burst of local mast cell degranulation. There is no tissue infiltration with cells, no late-phase component to the reaction, and therapy is dependent on antihistaminics or mast cell stabilizing agents. The nonsustained mediator release may be a result of the absence of a defined antigen, a very brief encounter with the initiating physical stimulus, and rapid removal of vasoactive substances and chemotactic factors so that the hive disappears quickly and a chemotactic factor gradient is not sustained so as to attract cells. Chronic urticaria differs in that the hive forms slowly, disappears over many hours, and is due to a perivascular accumulation of mononuclear cells and mast cells. These mononuclear cells appear to be critical for development of the lesion. Indirect evidence in support of this is the efficacy of corticosteroids in abrogating this type of hive and new concepts regarding mast cell proliferation and stimulation that are mononuclear cell-dependent.