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DEFINITION OF URTICARIA AND ANGIOEDEMA

Urticaria and angioedema represent the same pathophysiologic process occurring at different levels of the skin. Urticaria involves dilation of vascular structures in the superficial dermis, while angioedema originates from the deeper dermis and subcutaneous tissues. Not surprisingly they often appear together, with roughly 40% of patients reporting both, and affect >20% of the population at sometime during their lifespan. Urticaria can occur on any area of the body as well-circumscribed wheals with erythematous raised serpiginous borders and blanched centers that may coalesce to become giant wheals. Urticarial lesions last for <24 h, frequently migrate around the body, leave no bruising or scarring and are intensely pruritic. Angioedema is marked by dramatic swelling with more pain than pruritus and minimal erythema, which may develop with a pruritic prodrome and takes hours to days to resolve. Acute urticaria and/or angioedema are episodes that occur for <6 weeks’ duration, whereas attacks persisting >6 weeks are designated chronic.

Predisposing Factors and Etiology of Urticaria and Angioedema

Acute or chronic urticaria and/or angioedema can occur at any point in the lifespan with the third to fifth decade the most common for chronic. Women are affected more often than men with a slight predominance for those with a history of atopy. Acute urticaria is most often the result of exposure to a food, environmental or drug allergen or viral infection while chronic urticaria is often idiopathic.

The classification of urticaria-angioedema presented in Table 345-1 focuses on the different mechanisms for eliciting clinical disease and can be useful for differential diagnosis.

TABLE 345-1Classification of Urticaria and/or Angioedema

Additional etiologies include physical stimuli such as cold, heat, solar rays, exercise, and mechanical irritation. The physical urticarias can be distinguished by the precipitating event and other aspects of the clinical presentation. Dermographism, which occurs in 1–4% of the population, is defined by the appearance of a linear wheal with surrounding erythema at the site of a brisk stroke with a firm object (Fig. 345-3). Dermographism has a prevalence that peaks in the second to third decades. It is not influenced by atopy and has a duration generally of <5 years. Pressure urticaria, which often accompanies chronic idiopathic urticaria, presents in response to a sustained stimulus such as a shoulder strap or belt, running (feet), or manual labor (hands). Cholinergic ...

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