Hypersensitivity Reactions and Anaphylaxis

Abstract

Allergic reactions vary in intensity from mild rash or allergic rhinitis to devastating anaphylactic shock. Anaphylaxis, often underrecognized and undertreated, can be a life-threatening syndrome leading to multiorgan dysfunction. This review covers the etiology, pathophysiology, and treatment of severe allergic reactions and anaphylaxis. It is precipitated by exposure to particular allergens—commonly food, medications, insect stings, and environmental exposures—in a previously sensitized individual. Symptoms develop from an IgE-mediated immune response leading to degranulation of mast cells and basophils and the release of preformed mediators, lipid-derived metabolites, and inflammatory cytokines. First-line treatment for anaphylaxis involves epinephrine. Secondary treatments are antihistamines and corticosteroids. Further treatments for patients refractory to standard therapies involve vasopressor agents, nebulized albuterol, and glucagon. Frequency and duration of biphasic reactions are variable, limiting the development of consensus guidelines for monitoring of anaphylactic reactions. Figures show the immune activity and inflammatory pathways in allergic responses, mast cell degranulation, and a depiction of common organs involved and corresponding clinical manifestations. Tables list the criteria for diagnosis of anaphylaxis, classification of hypersensitivity reactions, common clinical manifestations, and etiology and mediators of anaphylaxis. This review contains 4 highly rendered figures, 11 tables, and 43 references. Key words: allergy, anaphylaxis, antihistamine, corticosteroid, epinephrine, mast cells