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.

As the lesions enlarge, they form round or irregularly shaped plaques. The central area may blister or become dusky in color; this change represents the necrosis of keratinocytes in areas of active involvement.

Erythema multiforme Figure 16-9 demonstrates the target-like quality of the variably sized and shaped plaques. Note the redness and edema at the border and the duskier appearance at the center. Mucosal lesions are not uncommon. Erythema multiforme is a self-healing disease, with an average duration of about 2 weeks.

The dorsum of the hand is a particularly common location. Herpes simplex infection is by far the most common etiologic agent. In some patients, frequent recurrences of herpes simplex and erythema multiforme require the use of prophylactic acyclovir or valacyclovir for extended periods of time. A wide variety of drugs, most commonly the sulfonamides, may also cause this syndrome.

Erythema multiforme Erythema multiforme tends to be acral in distribution. Figure 16-11 illustrates both bulla formation and the crusting of bullae that can occur during the course of the disease.

This plaque-like lesion on the elbow illustrates the edematous border and the dusky center, a result of the necrosis of keratinocytes. Erythema multiforme must be distinguished from urticaria multiforme (Figs. 16-21,16-22, 16-23, 16-24), which has some similar clinical features.

Stevens-Johnson syndrome/toxic epidermal necrolysis Drugs are the major etiologic factor in the development of this severe disorder. The most common agents are sulfonamides, anticonvulsants, and NSAIDs. Mycoplasma pneumoniae is the most commonly associated infectious agent. The cutaneous lesions include fixed erythematous macules, target lesions, and bullae.

There may be progression to widespread erythema and denudation, leaving underlying erosions. Frozen section processing of a biopsy specimen of toxic epidermal necrolysis allows for rapid diagnosis. In patients with erosions and blisters, one sees necrotic keratinocytes, severe degeneration of the basal layer, and a subepidermal separation.

Stevens-Johnson syndrome/toxic epidermal necrolysis The oral cavity is almost always involved, with bullae, ulcerations, and crusting most commonly presenting on the lips, buccal mucosa, and palate. Tracheal and bronchial involvement may result in breathing difficulty. Additionally, patients with Mycoplasma-induced Stevens-Johnson syndrome may have mucositis with minimal or absent skin lesions.

Ocular involvement frequently occurs in this syndrome, significantly affecting the bulbar conjunctiva. Long-term consequences include corneal damage and scarring, which may lead to permanent visual impairment.

Stevens-Johnson syndrome/toxic epidermal necrolysis Fever, headache, cough, and malaise are frequent features of this disorder. In addition to the lips (pictured in Fig. 16-17) and oral mucous membranes, esophageal involvement may lead to severe dysphagia and difficulty eating and drinking. Involvement of the vulva and vagina in girls, and glans penis in boys may cause dysuria and urinary retention.

In Figs. 16-17,16-18,16-19,16-20, note the extensive involvement with large and small bullous lesions. The mortality rate in this disease is significant; most deaths are related to superinfection and sepsis.