1. URTICARIA & ANGIOEDEMA
ESSENTIALS OF DIAGNOSIS
Eruptions of evanescent wheals or hives.
Itching is intense but, rarely, may be absent.
Special forms of urticaria have special features (dermatographism, cholinergic urticaria, solar urticaria, or cold urticaria).
Most incidents are acute and self-limited (1–2 weeks).
Chronic urticaria (episodes lasting longer than 6 weeks) may have an autoimmune basis.
Urticaria is defined as 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. The most common immunologic mechanism is mediated by IgE, as seen in the majority of patients with acute urticaria; another involves activation of the complement cascade. Some patients with chronic urticaria demonstrate autoantibodies directed against mast cell IgE receptors. ACE inhibitor and angiotensin receptor blocker therapy may be complicated by urticaria or angioedema. In general, extensive costly workups are not indicated in patients who have urticaria. A careful history and physical examination are more helpful.
Lesions are itchy, red swellings of a few millimeters to many centimeters (Figure 6–23). The morphology of the lesions may vary over a period of minutes to hours, resulting in geographic or bizarre patterns (eFigure 6–62). 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. In cholinergic urticaria, which is triggered by a rise in core body temperature (hot showers, exercise), wheals are 2–3 mm in diameter with a large surrounding red flare. Cold urticaria is acquired or inherited and triggered by exposure to cold and wind (see Chapter 37-08).
Urticaria (hives). (Reproduced, with permission, from Bondi EE, Jegasothy BV, Lazarus GS [editors]. Dermatology: Diagnosis & Treatment. Originally published by Appleton & Lange. Copyright © 1991 by The McGraw-Hill Companies, Inc.)
Urticaria. (Used, with permission, from TG Berger, MD, Dept Dermatology, UCSF.)
The most common causes of acute urticaria are foods, upper respiratory infections, and medications. The cause of chronic urticaria is often not found. Although laboratory studies are not likely to be helpful in the evaluation of acute or chronic urticaria, a complete blood count with differential, erythrocyte sedimentation rate, C-reactive protein, thyroid-stimulating hormone, and liver biochemical tests might be appropriate for some patients with chronic urticaria. In patients with individual lesions that persist past 24 hours, skin ...