Urticaria and Angioedema
Also known as hives, urticaria and angioedema are common allergic reactions. Urticaria is an episodic, rapidly occurring, usually self-limiting skin reaction. It involves only the superficial portion of the dermis, which erupts with local wheals surrounded by an erythematous flare. Angioedema, another dermal eruption, involves additional skin layers (including the subcutaneous tissue) and produces deeper, larger wheals (usually on the hands, feet, lips, genitalia, and eyelids). Angioedema causes diffuse swelling of loose subcutaneous tissue and also may affect the upper respiratory and GI tracts resulting in mild discomfort or life-threatening airway obstruction.
Urticaria and angioedema can occur separately or simultaneously, but angioedema may persist longer. Urticaria and angioedema affect about 20% of the general population at some time. Episodes tend to occur more often after adolescence, with the highest incidence in people in their 30s. Recurrent acute episodes last less than 6 weeks; episodes that persist longer than 6 weeks are considered chronic.
Causes
Urticaria and angioedema may result from allergy to drugs, foods, insect stings and, occasionally, inhalant allergens (animal danders and cosmetics) that provoke animmunoglobulin (Ig) E-mediated response to protein allergens. However, certain drugs may cause urticaria without an IgE response. When urticaria and angioedema are part of an anaphylactic reaction, they almost always persist long after the systemic response subsides because circulation to the skin is restored last after an allergic reaction. This slows histamine reabsorption at the reaction site.
Urticaria and angioedema not triggered by an allergen are probably also related to histamine release. External physical stimuli, such as cold (usually in young adults), heat, water, and sunlight, may also provoke urticaria and angioedema. Dermatographism, which develops after stroking or scratching the skin, may affect as much as 20% of the population. Such urticaria develops with varying pressure, most often under tight clothing, and is aggravated by scratching.
Several mechanisms and disorders may provoke urticaria and angioedema. These include IgE-induced release of mediators from cutaneous mast cells; binding of IgG or IgM to antigen, resulting in complement activation; and disorders such as localized or secondary infection (respiratory infection), neoplastic disease (Hodgkin’s disease), connective tissue diseases (systemic lupus erythematosus), collagen vascular disease, and psychogenic disease.
Complications
Skin abrasion and secondary infection may result from scratching. Angioedema that involves the upper respiratory tract may cause life-threatening laryngeal edema. GI involvement may cause severe abdominal colic that may lead to unnecessary surgery.
Assessment
The patient’s history may or may not reveal the source of the offending substance. Check the drug history, including nonprescription preparations, such as vitamins, aspirin, and antacids.
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