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For further information, see CMDT PART 6-32: REACTIVE ERYTHEMAS

Key Features

Essentials of Diagnosis

  • Evanescent wheals or hives

  • Intense itching; rarely, pruritus may be absent

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

  • Urticaria is divided into acute and chronic forms

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

General Considerations

  • Urticaria may be acute (less than 6 weeks' duration) or chronic (more than 6 weeks' duration)

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

    • Most common immunologic mechanism is mediated by IgE, which is seen in the majority of patients with acute urticaria

    • Another involves activation of the complement cascade

  • Cholinergic urticaria is triggered by a rise in core body temperature (hot showers, exercise)

  • Cold urticaria is acquired or inherited and triggered by exposure to cold and wind

  • Chronic urticaria

    • Termed "chronic spontaneous urticaria" when there is no identifiable trigger

    • Called chronic inducible urticaria when can be reproducibly triggered; for example

      • Cholinergic urticaria

      • Solar urticarias

      • Cold urticaria

      • Dermatographism

      • Delayed pressure urticaria

  • Some patients with chronic urticaria demonstrate autoantibodies directed against mast cell IgE receptors

  • Autoimmune thyroid disease may be associated with autoimmune urticaria

  • Acute hepatitis infection may be associated with urticarial vasculitis

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

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

  • Dermatographism

    • Induced by scratching

    • Can be elicited during the clinic visit by scratching the patient's skin

  • In cholinergic urticaria, 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


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




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