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Key Features

Essentials of Diagnosis

  • Eruptions of evanescent wheals or hives

  • Itching is intense, but rarely, may be absent

  • Special forms of urticaria have special features (dermographism; cholinergic, solar, or cold urticaria)

  • Most incidents are acute and self-limited (1–2 weeks)

  • Chronic urticaria (episodes lasting > 6 weeks) may have an autoimmune basis

General Considerations

  • Urticaria is defined as acute (< 6 weeks' duration) or chronic (> 6 weeks' duration)

  • The most common causes of acute urticaria are foods, infections, and medications

  • The cause of chronic urticaria is often not found

  • Urticaria can result from many different stimuli on an immunologic or nonimmunologic basis

  • Chief causes

    • Drugs

      • Aspirin

      • Nonsteroidal anti-inflammatory drugs

      • Angiotensin-converting enzyme

      • Angiotenin receptor blockers

      • Morphine

      • Codeine

    • Arthropod bites—eg, insect bites and bee stings (though the latter may cause anaphylaxis as well as angioedema)

    • Physical factors such as heat, cold, sunlight, and pressure; and, presumably, neurogenic factors, as in cholinergic urticaria induced by exercise, excitement, hot showers

  • Other causes

    • Penicillins and other medications

    • Inhalants such as feathers and animal danders

    • Ingestion of shellfish, tomatoes, or strawberries

    • Infections such as viral hepatitis (causing urticarial vasculitis)

    • Salicylates and tartrazine dyes

Clinical Findings

Symptoms and Signs

  • Lesions are itchy red swellings of a few millimeters to many centimeters

  • The morphology of the lesions may vary over a period of minutes to hours

  • Individual lesions in true urticaria last less than 24 h, and often only 2–4 h

  • Angioedema is involvement of deeper vessels, with swelling of the lips, eyelids, palms, soles, and genitalia in association with more typical lesions

  • Angioedema is no more likely than urticaria to be associated with systemic complications such as laryngeal edema or hypotension

  • In cholinergic urticaria, triggered by a rise in core body temperature (hot showers, exercise), wheals are 2–3 mm in diameter with a large surrounding red flare

Differential Diagnosis

  • Vasculitis

  • Erythema multiforme

  • Contact dermatitis (eg, poison oak or ivy)

  • Cellulitis

Diagnosis

Laboratory Tests

  • Laboratory studies are not likely to be helpful in the evaluation of acute or chronic urticaria unless there are suggestive findings in the history and physical examination

  • A complete blood count with differential, erythrocyte sedimentation rate or C-reactive protein, thyroid-stimulating hormone, and liver chemistries might be appropriate for some patients with chronic urticaria

  • Functional ELISA test can detect patients with an autoimmune basis for their chronic urticaria

Diagnostic Procedures

  • In patients with individual lesions that persist past 24 h, a skin biopsy may confirm neutrophilic urticaria or urticarial vasculitis

Treatment

Medications

  • H1-antihistamines

    • Hydroxyzine, 10 mg twice daily orally to 25 mg three times daily or as a single nightly dose of 50–75 mg to reduce daytime sedation, is initial therapy

    • Cyproheptadine, 4 mg ...

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