ESSENTIALS OF DIAGNOSIS
Evanescent wheals or hives with or without angioedema.
Intense itching; very rarely, pruritus may be absent.
Urticaria is divided into acute and chronic forms.
Most episodes are acute and self-limited (1–2 weeks).
Chronic urticaria (lasting > 6 weeks) may have an autoimmune basis.
Urticaria involves hives, angioedema, or both. It may be acute or chronic (more than 6-week duration). Chronic urticaria is further divided into chronic spontaneous urticaria and chronic inducible urticaria. Chronic inducible urticaria is reproducibly triggered by specific exposures. Examples include cholinergic urticaria, solar urticaria, cold urticaria, dermatographism, and delayed pressure urticaria. 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). Some patients with chronic spontaneous urticaria demonstrate autoantibodies directed against mast cell IgE receptors.
Lesions are itchy, red swellings of a few millimeters to many centimeters (Figure 6–33). The morphology of the lesions may vary over a period of minutes to hours, resulting in geographic or bizarre patterns (eFigure 6–101). Individual lesions in true urticaria last less than 24 hours and often only 2–4 hours. Angioedema is involvement of deeper subcutaneous tissue 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 is induced by scratching the skin and can be elicited during the clinic visit. The wheals of cholinergic urticaria are 2–3 mm in diameter with a large surrounding red flare.
Urticaria. (Used, with permission, from TG Berger, MD, Dept Dermatology, UCSF.)
Urticaria on back. Multiple annular wheals with central clearing. (Reproduced with permission from Soutor C, Hordinsky MK. Clinical Dermatology. New York; McGraw-Hill Companies, 2013.)
The most common causes of acute urticaria are foods, upper respiratory infections, and medications. The cause of chronic spontaneous urticaria is often not found. Although laboratory studies are not generally helpful in the evaluation of acute or chronic urticaria, a CBC with differential, ESR, CRP, TSH, and liver biochemical tests may be appropriate for some patients with chronic urticaria. Elevated inflammatory markers suggest an alternate diagnosis. In patients with individual lesions that persist past 24 hours, skin biopsy may confirm neutrophilic urticaria or urticarial vasculitis. A functional ELISA test looking for antibodies against the high-affinity receptor for IgE (Fc-Epislon RI) can identify those who may have an autoimmune basis for their chronic urticaria.