Acute and chronic urticaria and angioedema.

Urticaria and angioedema are clinical manifestations of various immunologic and inflammatory mechanisms, or they may be idiopathic. The respiratory and gastrointestinal tracts as well as the cardiovascular system may be involved in any combination. Patients with urticaria and/or angioedema can be classified based on pathophysiologic mechanisms into those with IgE-dependent or complement-mediated immunologic disorders, those with nonimmunologic disorders in which there is a direct effect on the mast cell or on arachidonic acid metabolism, and those whose condition is idiopathic. Evaluation of patients should focus on a thorough history. Laboratory tests provide minimal additional information. About one half of patients with urticaria alone and 25% with urticaria and angioedema or angioedema alone are free of lesions within 1 year. With urticaria, angioedema, or both, 20% of patients experience episodes for more than 20 years.