A 26-year-old man was prescribed trimethoprim-sulfamethoxazole for sinusitis and broke out in hives 1 week later. The hives were all over his trunk and arms (Figures 156-1 and 156-2). He denied throat tightening, trouble breathing, and lip or periorbital swelling. His sinus symptoms were mostly resolved, so he was told to stop the antibiotic and take an oral antihistamine. The H1-blocker gave him relief of symptoms, and the urticaria disappeared over the next 2 days.
A 26-year-old man with acute urticaria due to trimethoprim-sulfamethoxazole. (Reproduced with permission from Richard P. Usatine, MD.)
Note the confluence of wheals with a well-demarcated border on the arm of the man with acute urticaria due to trimethoprim-sulfamethoxazole. (Reproduced with permission from Richard P. Usatine, MD.)
Urticaria is a common disorder characterized by transient skin or mucosal swellings that develop secondary to plasma leakage. The clinical presentation is determined by the depth of swelling. Superficial dermal swellings present as transient, pink, pruritic swellings known as wheals. Deeper swellings of the dermis, subcutaneous, or mucosal tissue present as flesh-colored to pink, painful, less well-defined swellings known as angioedema.1 Urticaria and angioedema result from a large variety of underlying causes, are elicited by a great diversity of factors, and present clinically in a highly variable way.2 Standard hives with transient wheals is the most common manifestation of urticaria.
It is estimated that 15% to 25% of the population may have urticaria sometime during their lifetime.2
Urticaria affects 6% to 7% of preschool children and 17% of children with atopic dermatitis.3 Viral infections are a common cause of urticaria in children.
Among all affected age groups, approximately 50% have both urticaria and angioedema, 40% have isolated urticaria, and 10% have angioedema alone.3
Acute urticaria is defined as less than 6 weeks' duration. A specific cause is more likely to be identified in acute urticaria.3
The cause of chronic urticaria (>6 weeks' duration) is determined in less than 20% of cases.3
Chronic urticaria is twice as common in women as in men.4
Chronic urticaria predominantly affects adults, with peak incidence occurring between ages 20 and 40.4
Up to 40% of patients with chronic urticaria of more than 6 months' duration still have urticaria 10 years later.4
Chronic urticaria is more prevalent in those with autoimmune disorders.5,6 Hashimoto thyroiditis is the most commonly associated autoimmune disease.6
ETIOLOGY AND PATHOPHYSIOLOGY