Angioedema, and Anaphylaxis
نویسندگان
چکیده
The human immune system is an assemblage of cellular and humoral components working together in a highly complex, coordinated, and elegant fashion to achieve the primary goal of protecting the human host (self) from harmful offenders (nonself). Exposure to danger signals activates the various immune mechanisms to bring about immune responses aimed at neutralizing the dangerous nonself while preserving self. The immune system can, however, overreact to otherwise harmless nonself agents, producing inappropriate responses that are harmful to the host, thereby giving rise to allergy or allergic diseases. These hypersensitivity reactions are manifested in clinical symptoms ranging from mildly inconvenient to debilitating to fatal. For practical purposes, the term allergy is used in this chapter to refer to mast cell–mediated hypersensitivity reactions. For most allergic diseases to occur, predisposed individuals need to be exposed to allergens through a process called sensitization. Substances that elicit an allergic reaction are referred to as allergens, and those that elicit an antibody response (activated by Band T-cell receptors) are called antigens. In this allergic continuum, there are several important allergic syndromes frequently encountered in the emergency department (ED). Urticaria is a common allergic reaction to foods, drugs, or physical stimuli and is clinically characterized by a red itchy rash. Angioedema is the other important allergic syndrome, mediated by either an allergic mechanism in response to exposure to foods, drugs, or physical stimuli or a nonallergic mechanism (e.g., angiotensin-converting enzyme [ACE] inhibitor). Angioedema is characterized by swelling of the subcutaneous tissues, which can cause airway difficulty if the larynx is involved. At the other extreme of this allergic continuum is anaphylaxis, a life-threatening systemic allergic reaction characterized by acute onset and multiorgan involvement. The term anaphylaxis is derived from Greek (ana, against; phylax, guard or protect), meaning “against protection.” Mechanistically, anaphylaxis is a type I hypersensitivity reaction (allergic), mediated by immunoglobulin E (IgE). In its most common form, anaphylaxis is precipitated by exposure to allergens in previously sensitized individuals. Timely recognition of the syndrome and proper care are essential to bring about beneficial outcomes for patients with anaphylaxis. The term anaphylactoid reaction refers to a syndrome clinically similar to anaphylaxis that is not mediated by IgE. Its clinical presentation and treatment are identical to those of anaphylaxis. Anaphylactoid reactions appear to result from direct degranulation of mast cells (and basophils) and may follow a single, first-time exposure to certain inciting agents. In this chapter, we use the term anaphylaxis to refer to both IgEand non–IgE-mediated reactions, obviating the need for the term anaphylactoid reaction. Epidemiology and Risk Factors
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