Anaphylaxis, Urticaria, & Angioedema

Introduction

Essentials of Diagnosis

• Anaphylaxis is a systemic reaction with cutaneous symptoms, associated with dyspnea, visceral edema, and hypotension.
  
• Urticaria is characterized by large, irregularly shaped, pruritic, erythematous wheals.
  
• Angioedema is painless, deep, subcutaneous swelling, often involving periorbital, circumoral, and facial regions.
  
• These disorders may be diagnosed clinically, especially in the context of allergen exposure; detection of specific IgE or elevated serum tryptase can confirm the diagnosis.

General Considerations

Certain allergens - especially drugs, insect venoms, and foods - may induce an IgE antibody response, causing a generalized release of mediators from mast cells and resulting in systemic anaphylaxis. This potentially fatal condition affects both nonatopic and atopic persons. Isolated urticaria and angioedema are more common cutaneous forms of anaphylaxis with a better prognosis.

Food allergies cause an estimated 150 fatalities per year in the United States, most cases being due to ingestion of peanuts, tree nuts, shellfish, and fish. Common childhood food allergies such as milk, soy, wheat, and egg are often outgrown over time if strict avoidance is practiced. ß-Lactam antibiotics may be involved in 400-800 fatalities per year, and stinging insect venom causes about 50 fatalities per year. Chronic relapsing urticaria, angioedema, and, less commonly, anaphylaxis, however, are not always due to IgE-mediated hypersensitivity. In a minority of cases - perhaps 10% or less - underlying systemic disorders such as systemic mastocytosis or subclinical infection or inflammatory disorders may be manifested by episodic urticaria or angioedema. Idiopathic causes may also be responsible for chronic or relapsing symptoms, suggesting that some cases may be associated with autoimmune processes including the production of histamine-liberating autoantibodies directed against Fce mast cell membrane receptors. Twenty percent of the population will experience urticaria or angioedema during their lifetime, and the estimated prevalence of idiopathic anaphylaxis is 34,000 patients in the United States.

Clinical Findings

A. Symptoms and Signs
The manifestations are (1) hypotension or shock from widespread vasodilation, (2) respiratory distress from bronchospasm or laryngeal edema, (3) gastrointestinal and uterine muscle contraction, and (4) urticaria and angioedema.

B. Laboratory Findings
In vivo allergy skin testing and in vitro RAST testing can detect allergen-specific IgE for a variety of foods, hymenoptera (bee, wasp, hornet, fire ant) venom, latex, and some medicines. Skin testing for food allergy is appropriate only if the patient has symptoms consistent with IgE-mediated allergy (eg, urticaria, angioedema, or anaphylaxis) within 2 hours after eating the suspect food.