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For further information, see CMDT PART 6-32: REACTIVE ERYTHEMAS
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Essentials of Diagnosis
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Eruptions of evanescent wheals or hives with or without angioedema
Itching is intense, but very rarely, may be absent
Urticaria is divided into acute and chronic forms
Most incidents are acute and self-limited (1–2 weeks)
Chronic urticaria (lasting > 6 weeks) may have an autoimmune basis
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General Considerations
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Urticaria is defined as acute (< 6 weeks' duration) or chronic (> 6 weeks' duration)
Chronic urticaria is further divided into chronic spontaneous urticaria and chronic inducible urticaria
Chronic inducible urticaria is reproducibly triggered by specific exposures, such as
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Hives or angioedema or both
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 < 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
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Differential Diagnosis
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True urticaria should be differentiated from diseases that present with similar lesions that are not true urticaria (eg, adult-onset Still disease, urticarial vasculitis, and cryopyrin associated periodic syndromes)
Vasculitis
Erythema multiforme
Contact dermatitis (eg, poison oak or ivy)
Cellulitis
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Laboratory studies are generally not 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 may be appropriate for some patients with chronic urticaria
Functional ELISA test can detect patients with an autoimmune basis for their chronic urticaria
Some patients with chronic spontaneous urticaria demonstrate autoantibodies directed against mast cell IgE receptors
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Diagnostic Procedures
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