Urticaria, commonly known as "hives," can be acute or chronic, and the numerous triggers include drugs, food, infections, arthropods, autoimmune disease, and stress. The wheals consist of circumscribed areas of raised erythematous plaques that are often annular and very pruritic (Fig. 33-67).
These wheals can occur on any skin area and are transient and migratory. The acute form of urticaria lasts less than 4 to 6 weeks, and the chronic form lasts more than 6 weeks. When there is an obvious new drug causing the eruption, the causation is easy to determine.
For patients on multiple medications and no evidence of infection or illness, diagnosis can be very difficult. Skin prick testing or radioallergosorbent assay testing (RAST) testing, typically done through an allergy specialist, may help determine the cause but may be elusive. Patients with chronic urticaria unresponsive to antihistamines require an extensive workup. In more than 50% cases of chronic urticaria, no etiology is found, and it is considered idiopathic or chronic "autoimmune" urticaria.
The mainstay of therapy for urticaria is avoidance of known triggering agents and antihistamines. Classic antihistamines are effective (diphenhydramine, hydroxyzine, doxepin), but sedation limits their use to primarily nighttime dosing. Second-generation and third-generation antihistamines are helpful for daytime use (cetirizine, loratadine, fexofenadine, desloratadine, levocetirizine). Oral corticosteroids are useful but should be limited to short-term therapy of severe acute urticaria. H2-receptor antagonists (cimetidine, ranitidine, famotidine) and leukotriene antagonists are sometimes helpful as adjunctive therapy.
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