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DERMATOLOGY*

*The authors acknowledge the special contributions of Falguni Asrani, MD, to prior edition.

URTICARIA

Clinical Features

Urticaria, or hives, are pruritic raised erythematous superficial skin wheals that arise in response to histamine, leukotrienes, prostaglandins, and other substances released by stimulated mast cells. Lesions develop and resolve quickly; individual lesions should resolve in <24 hours. Urticaria is often associated with hypersensitivity reactions, including anaphylaxis. Triggers can include allergic reactions to drugs, foods, insect stings, and rarely aeroallergens. The 2017 guidelines by the National Institute of Allergy and Infectious Diseases recommend introducing all foods including highly allergenic foods such as peanuts, tree nuts, milk, egg, wheat, soy, and shellfish between 5 and 12 months of age, which may result in younger presentations of patient with acute urticaria from food. Infections including hepatitis, Epstein-Barr virus, Lyme disease, Helicobacter pylori, helminths, and fungi have been associated with urticaria. In areas where the lone star tick is endemic, there are growing cases of delayed anaphylaxis after ingesting mammalian meat. The reactions can occur up to 48 hours after ingestion from an antibody to alpha-gal, which is a carbohydrate on mammalian meat. Chronic urticaria is when the patient has had symptoms for over 6 weeks. Chronic urticaria can also be caused by physical stimuli including cold, heat, or exercise (cholinergic), pressure, vibration, and sun exposure. Patients with collagen vascular and autoimmune diseases often present with urticaria. Differential diagnosis includes mastocytosis/urticaria pigmentosa (UP), erythema multiforme (EM), bullous skin disorders, or dermatitis herpetiformis. Obtaining a detailed history can help identify an etiology. Urticaria that has been occurring for <6 weeks rarely requires any laboratory workup. Obtaining specific immunoglobulin (Ig) E levels in an acute setting can reflect a falsely negative result. Laboratory tests may be done as indicated for chronic urticaria. Helminth infections and allergies would be associated with eosinophilia.

FIGURE 7.1

Acute Urticaria with Chemosis; Anaphylaxis. Erythematous, serpiginous lesions with well-demarcated edges (A) and conjunctival edema (B) associated with wheezing were seen in this patient. (Photo contributor: Ee Tay, MD.)

FIGURE 7.2

Acute Urticaria. (A, B) An infant with acute urticaria. Etiology of lesions often is undetermined. (Photo contributor: Dawn Davis, MD.)

FIGURE 7.3

Dermographism. This “rash” was produced within 3 minutes of stroking the skin with a tongue blade. Dermographism (ability to write on the skin) is an example of physical urticaria. Triggering factors may include contact with clothing, towels, or sheets. It can also occur as an isolated disorder. Linear pruritic wheals appear on skin within 2 to 5 minutes of stroking and usually resolve within 30 minutes to 3 hours. Most patients are without any systemic symptoms. (Photo contributor: Binita R. Shah, MD.)

Emergency Department Treatment and Disposition

Attempt to identify the trigger based on a thorough history. Advise patients to discontinue or avoid the offending agent, if known. Treatment of urticaria includes oral and sometimes parentally administered H1 blockers (eg, diphenhydramine). Second-generation antihistamines (eg, cetirizine) can be used once or twice a day until symptoms resolve. H2 blockers (eg, cimetidine, ranitidine) ...

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