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INTRODUCTION TO CHAPTER

Urticaria and cutaneous adverse drug reactions are among the most common skin problems seen in the clinic and hospital. They can be associated with urgent medical conditions such as laryngeal edema and toxic epidermal necrolysis. It is important for a clinician to identify the underlying causes for these disorders.

URTICARIA

Introduction

Urticaria (hives) is characterized by the rapid onset of lesions called wheals that consist of a central mid-dermal swelling with or without surrounding erythema, with associated pruritus, lasting anywhere from 1 to 24 hours. Associated angioedema can sometimes be seen, characterized by swelling of the deeper dermis and subcutaneous tissue lasting up to 72 hours.1 The lifetime prevalence of urticaria is estimated to be approximately 20% and it can present in patients ranging in age from infants to the elderly. Urticaria can be divided into acute and chronic forms and urticaria elicited by physical factors. Acute urticaria is defined as urticaria of less than 6 weeks duration, whereas chronic urticaria lasts more than 6 weeks. Only 5% of patients with urticaria will be symptomatic for more than 4 weeks.

Pathophysiology

The underlying event leading to urticaria is mast cell degranulation, with release of histamine and other pro-inflammatory molecules. There are numerous stimuli that can lead to mast cell activation through various pathways. The most common cause of acute urticaria is viral infections, particularly of the upper respiratory tract.2 Other common causes of acute urticaria are listed in Table 14-1. Food-induced type I hypersensitivity reactions are a rare cause of acute urticaria in adults, but are a more common cause in children.3

Table 14-1.

Causes of acute urticaria.

Chronic urticaria can be associated with rheumatologic disorders, chronic infections including Hepatitis B and C, sinus infections and Helicobacter pylori, as well as parasitic infections (more common in developing countries).1 In the majority of patients with chronic urticaria, an underlying disease will not be found. Approximately 35% to 40% of cases of chronic urticaria area caused by autoantibodies directed against the IgE receptor of mast cells.4

Angioedema occurs with wheals in approximately 40% of cases of ...

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