A penicillin allergic young boy was given trimethoprim-sulfamethoxazole for otitis media and broke out in hives one week later. The hives were on his trunk and arms (Figure 134-1). He had no airway symptoms and had only urticaria without angioedema. His fever was gone, his ear pain was resolved, and his tympanic membranes were not bulging, so his parents were told to stop the antibiotic. The pediatrician prescribed an H₁-blocker that gave him relief of symptoms and the wheals disappeared over the next 2 days.

Urticaria and angioedema are a heterogeneous group of diseases that cause swelling of the skin and other soft tissues. They both result from a large variety of underlying causes, are elicited by a great diversity of factors, and present clinically in a highly variable way.¹ Standard hives with transient wheals is the most common manifestation of urticaria.

Hives.

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  It is estimated that 15 to 25 percent of the population may have urticaria sometime during their lifetime.²

  
  
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  Urticaria affects 6 to 7 percent of preschool children and 17 percent of children with atopic dermatitis.²

  
  
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  Among all age groups, approximately 50 percent have both urticaria and angioedema, 40 percent have isolated urticaria, and 10 percent have angioedema alone.²

  
  
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  Acute urticaria is defined as less than 6 weeks’ duration. A specific cause is more likely to be identified in acute urticaria.²

  
  
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  The cause of chronic urticaria (>6 weeks’ duration) is determined in less than 20 percent of cases.²

  
  
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  Chronic urticaria predominantly affects adults.³

  
  
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  Up to 40 percent of patients with chronic urticaria of more than 6 months’ duration still have urticaria 10 years later.³

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  The pathophysiology of angioedema and urticaria can be immunoglobulin (Ig) E mediated, complement mediated, related to physical stimuli, autoantibody mediated, or idiopathic.

  
  
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  These mechanisms lead to mast cell degranulation resulting in the release of histamine. The histamine and other inflammatory mediators produce the wheals, edema, and pruritus.

  
  
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  Urticaria is a dynamic process in which new wheals evolve as old ones resolve. These wheals result from localized capillary vasodilation, followed by transudation of protein-rich fluid into the surrounding skin. The wheals resolve when the fluid is slowly reabsorbed.

  
  
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  Angioedema is an edematous area that involves transudation of fluid into the dermis and subcutaneous tissue (Figures 134-2 and 134-3).

The following etiologic types exist:

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  Immunologic—IgE mediated, complement mediated. Occurs more often in patients with an atopic background. Antigens are most commonly foods or medications. The most common foods are milk, nuts, wheat, and shellfish.

  
  
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  Physical urticaria—Dermatographism, cold, cholinergic, solar, pressure, and vibratory urticaria (Figures 134-4 to 134-6).

  
  
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  Urticaria caused by mast cell-releasing agents—Mastocytosis and urticaria pigmentosa (Figures 134-7 and 134-8).

  
  
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  Urticaria associated with vascular/connective tissue autoimmune disease.

  
  
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  Hereditary angioedema is a potentially life-threatening disorder that is inherited in an autosomal dominant manner. In this disease, angioedema occurs without urticaria.