Urticaria A wheal is an edematous papule that may enlarge to form a pink, sharply circumscribed, elevated plaque. The typical lesions of urticaria, pictured in Figs. 16-1 and 16-2, have a suggestion of central clearing.
By definition, the individual lesions of urticaria evolve quickly and resolve within 24 to 48 hours. They are usually accompanied by severe pruritus. Urticaria is an extremely common disorder, and the etiology often remains unknown. In most children, the problem resolves spontaneously over time.
Urticaria Larger, more geographic lesions are pictured in Figs. 16-3 and 16-4. In the cases where a cause is established, the most common etiologies of urticaria are medications, foods (eg, nuts, strawberries, shellfish, and other seafoods), and viral and bacterial infections.
Autoimmune disease, such as autoimmune thyroiditis, and malignancy are extremely rare causes. In the child with chronic urticaria, it is often difficult or impossible to identify a single cause. In these patients, one attempts to control the development of new lesions with a daily schedule of nonsedating antihistamines.
Physical urticarias There are urticarias in which stroking, pressure, cold, heat, or sun exposure are causative. Figure 16-5 shows a wheal produced by stroking the skin with a degree of force that would ordinarily cause nothing more than transient erythema. The phenomenon, called dermographism, is present in a small percentage of normal individuals.
Figure 16-6 shows a large wheal produced by resting an ice cube on the forearm. Cold-induced urticaria may be acquired or inherited. In the most common, acquired form, patients develop lesions shortly after ingesting cold foods or liquids or shortly after exposure to a drop in environmental temperature. Patients with this form of sensitivity are at risk for laryngeal edema or circulatory collapse as a result of significant cold exposure. Antihistamines or doxepin are of some help in preventing attacks. In a very rare syndrome, contact of the skin with water, without respect to its temperature, produces wheals (aquagenic urticaria).
Erythema multiforme This disorder is termed multiforme because the morphology of its lesions is so variable. The primary lesion is most often an erythematous macule that evolves into a papule. Early in the course, these lesions may easily be mistaken for urticaria.
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