Excerpt from Urticaria, Chronic

Synonyms, Key Words, and Related Terms: hives, wheals, allergy, allergic reaction, anaphylaxis, anaphylactoid reaction, angioedema

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Background: Chronic urticaria, defined as urticaria that persists for longer than 6 weeks, is a frustrating condition for both patients and caregivers. Urticaria is not a single disease but a reaction pattern that represents cutaneous mast cell degranulation, resulting in extravasation of plasma into the dermis. Urticaria is characterized by hives or wheals, which are edematous, and often pruritic, skin papules or plaques. The variety of potential triggers of urticaria can make the approach to diagnosis and treatment a challenge. Without correction of the underlying problem, patients with chronic urticaria may not improve or may depend on medication for many years to get relief.

The primary subgroups of chronic urticarias include the physical urticarias, urticaria secondary to an underlying medical condition, and chronic idiopathic urticaria (CIU). Physical urticarias, which are reproducible with the appropriate stimuli, can be identified with a thorough history and challenge testing.

Traditionally, the approach in patients with chronic urticaria (when physical etiology has been excluded) has been to order a panel of laboratory tests to uncover an occult medical condition responsible for the skin findings. Although many causes of chronic urticaria exist, in most patients, an extensive workup does not uncover an etiology. Fortunately, urticaria rarely is the sole manifestation of an underlying medical problem. Patients in whom no explanation for the urticaria is established are said to have CIU; however, recent findings suggest that in 25-45% of patients, CIU is not idiopathic but is an autoimmune disease.

An important entity in the differential diagnosis of chronic urticaria is urticarial vasculitis. A forme fruste of leukocytoclastic vasculitis, urticarial vasculitis may be associated with internal organ involvement.

Pathophysiology: The mast cell is the primary agent in the pathogenesis of urticaria. Mast cell stimulation results in the release of both preformed (histamine) and newly formed (prostaglandins) mediators from cytoplasmic granules, which cause wheal formation, vasodilatation, and erythema. Mast cells also release chemoattractants for other cells (eg, neutrophils) that also are involved in wheal formation. A number of agents may be involved in the pathogenesis of urticaria, which may explain why antihistamines are not always effective therapy.

Release of mediators by mast cells may be caused by both immune and nonimmune mechanisms. FceRIa on the mast cell surface is a high-affinity immunoglobulin E (IgE) receptor that binds the Fc portion of IgE, resulting in histamine release. Immunoglobulin G autoantibodies to this receptor appear to be the etiologic factor in as many as 25% of patients with CIU. Other agents, such as aspirin, opioids, and adenosine, cause mast cell degranulation directly through nonimmunologic means.

Frequency:

In the US: Overall, urticaria is reported to affect as many as 25% of people at some point in their lives. True incidence of CIU is unknown; however, it is believed to occur in 0.1-3% of the population.

Internationally: The incidence is the same as in the United States.

Mortality/Morbidity: Unlike angioedema, which may affect the airway, urticaria is not a life-threatening disease; however, chronic urticaria has been shown to have a negative impact on the quality of life of affected patients. In a study by O'Donnell et al, the effects of chronic urticaria on the activities of daily living, social interactions, rest, and work were found to be similar to those experienced by patients with heart disease.

Race: Urticaria affects persons of all races.

Sex: Both sexes are affected; how .....