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 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 may affect the upper respiratory and GI tracts.
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 are more common after adolescence, with the highest incidence in people who are in their 30s. Recurrent acute episodes last less than 6 weeks; if episodes persist longer than 6 weeks, the condition is considered chronic.
Urticaria and angioedema may result from allergy to drugs, foods, insect stings and, occasionally, inhalant allergens (animal dander, cosmetics) that provoke an immunoglobulin (lg) E-mediated response to protein allergens. 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 that aren't 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.
Angioedema without urticaria occurs with C1 inhibitor deficiency, which can occur as an autosomal dominant characteristic (hereditary angioedema) or be acquired with lymphoproliferative disorders.
Several mechanisms and disorders may provoke urticaria and angioedema. They include IgE-induced release of mediators from cutaneous mast cells; binding of IgG or IgM to antigen, resulting in complement activation; and such disorders as localized or secondary infection (respiratory tract infection), neoplastic disease (Hodgkin's disease), connective tissue diseases (systemic lupus erythematosus), collagen vascular disease, and psychogenic disease.
Urticarial lesions itch, have a central white wheal that is elevated, and are surrounded by an erythematous halo. The lesions are typically rounded and circumscribed. Characteristically, hives should blanch with pressure; they generally resolve within 24 hours, leaving no residual change to the skin.
Swelling of deeper layers of the skin, angioedema, commonly accompanies urticaria. This swelling often results from the same inflammatory processes that cause hives. The redness that is seen surrounding superficial lesions is not observed, though the swelling is readily appreciated. Angioedema generally occurs on the extremities and digits as well as areas of the head, neck, face, and in men, genitalia. It is often described as being painful or burning.
Your doctor will need to ask many questions in an attempt to find the possible cause. Since there are no specific tests for hives or the associated swelling of angioedema, testing will depend on your medical history and a thorough examination by your dermatologist. Skin tests may be performed to determine the substance that you are allergic to. Routine blood tests are done to determine if a systemic illness is present.
Appropriate treatment prevents or limits the patient's contact with triggering factors. When the triggering stimulus has been removed, urticaria usually subsides in a few days, unless it results from a drug reaction. Then it may persist for as long as the drug remains in the tissues.
Treatment may involve desensitization to the triggering antigen. During desensitization, progressively larger doses of specific antigens (identified by skin testing) are injected intradermally. Diphenhydramine or another antihistamine can ease itching and swelling.
© Doctor-clinic.org. All rights reserved.
Bookmark This Page: