Urticaria, commonly known as hives, is an episodic, usually self-limited skin reaction characterized by local dermal wheals surrounded by an erythematous flare. Angioedema, which can present either subcutaneously or dermally, produces deeper, larger wheals (usually on the hands, feet, lips, genitals, and eyelids) and a more diffuse swelling of loose subcutaneous tissue. Urticaria and angioedema can occur simultaneously, but angioedema may last longer.
Urticaria and angioedema are common allergic reactions. Causes include allergy to drugs, foods, insect stings and, occasionally, inhalants, such as animal dander and cosmetics, that provoke an immunoglobulin (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 has subsided. This occurs because circulation to the skin is inhibited after an allergic reaction, which results in slow histamine reabsorption at the reaction site. Nonallergic urticaria and angioedema are probably also related to histamine release.
External physical stimuli, such as cold (usually in young adults), heat, water, or sunlight, may provoke urticaria and angioedema. Dermographism urticaria develops with varying pressure, usually under tight clothing, and is aggravated by scratching.
Several different mechanisms and underlying disorders may provoke urticaria and angioedema. These include IgE-induced release of mediators from cutaneous mast cells; binding of IgG or IgM, resulting in complement activation; localized or secondary infections such as respiratory infection; neoplastic diseases such as Hodgkin’s disease; connective tissue diseases such as systemic lupus erythematosus; collagen vascular diseases; and psychogenic diseases.
Signs and symptoms
The characteristic features of urticaria are distinct, raised, evanescent dermal wheals surrounded by an erythematous flare. These lesions may vary in size. In cholinergic urticaria, the wheals may be tiny and blanched, surrounded by erythematous flares.
Angioedema characteristically produces nonpitted swelling of deep subcutaneous tissue, usually on the eyelids, lips, genitalia, and mucous membranes. These swellings don’t usually itch but may burn and tingle.
An accurate patient history can help determine the cause of urticaria. Such a history should include:
drug history, including over-the-counter preparations (vitamins, aspirin, and antacids)
frequently ingested foods (strawberries, milk products, fish)
environmental influences (pets, carpet, clothing, soap, inhalants, cosmetics, hair dye, and insect bites and stings).
Diagnosis also requires physical assessment to rule out similar conditions, as well as a complete blood count, urinalysis, erythrocyte sedimentation rate, and a chest X-ray to rule out inflammatory infections. Skin testing, an elimination diet, and a food diary (recording time and amount of food eaten and circumstances) can pinpoint provoking allergens. The food diary may also suggest other allergies. For instance, a patient allergic to fish may also be allergic to iodine contrast materials.
Recurrent angioedema without urticaria, along with a familial history, points to hereditary angioedema. Decreased serum levels of complement 4 and complement 1 esterase inhibitors confirm this diagnosis.
Treatment aims to prevent or limit contact with triggering factors or, if this is impossible, to desensitize the patient to them and relieve symptoms. Once the triggering stimulus has been removed, urticaria usually subsides in a few days. (Drug reactions may persist until the drug is no longer in the bloodstream.)
During desensitization, progressively larger doses of specific antigens (determined by skin testing) are injected intradermally. Antihistamines such as hydroxyzine can ease itching and swelling in every kind of urticaria, although they may induce drowsiness.
Corticosteroid therapy may be necessary for some patients.
VN:F [1.9.20_1166]Urticaria and angioedema,