Chapter 21: Urticaria and angioedema.

Urticaria, also known as hives, may affect up to 20% of the population at some time in their lives. Urticaria is characterized by extreme pruritus and described as erythematous, raised, circumscribed lesions with central pallor that blanch with pressure. The pathogenesis of urticaria involves mast cell activation, with subsequent release of histamine and other vasoactive mediators, leading to increased vascular permeability of postcapillary venules and development of edema, erythema, and pruritus. Urticaria is closely associated with angioedema in 40% of individuals; ∼10% of patients experience angioedema without urticaria. Urticarial lesions often are generalized with multiple lesions in no specific distribution; angioedema tends to be localized, commonly affecting the face (periorbital and perioral regions), tongue, uvula, soft palate or larynx, extremities, and genitalia. Urticaria is subdivided into acute and chronic urticaria based on duration of symptoms. Acute urticaria lasts <6 weeks and an identifiable cause may be discovered such as food products, medications (aspirin, nonsteroidal anti-inflammatory drugs, and antibiotics), or insect stings. Urticaria lasting >6 weeks is designated as chronic urticaria, and an etiology is seldom identified and thus considered idiopathic. Chronic urticaria may have an autoimmune basis. There is a well-documented association between autoimmune hypothyroidism (Hashimoto's disease) and urticaria and angioedema with higher incidence of antithyroid (antithyroglobulin and antiperoxidase) antibodies in these usually euthyroid patients. Furthermore, studies have revealed a circulating IgG antibody directed against the IgE receptor (F(Cε)RIα) or IgE in 40-60% of patients with chronic urticaria. Histamine 1-receptor antagonists (antihistamines) are initial therapy.