Urticaria, Angioedema, and Anaphylaxis
Fred S. Rosen MD1
1 James L. Gamble Professor of Pediatrics, Harvard Medical School, Center for Blood Research and Children's Hospital, Boston, MA 02115
Urticaria, angioedema, and anaphylaxis are different manifestations of immediate hypersensitivity. Immediate hypersensitivity is an untoward, immunologically mediated reaction that occurs within minutes to a few hours of the introduction of antigen into an immune individual and that is mediated by antibodies; thus, these reactions also have been called antibody-mediated hypersensitivity. Approximately 20% of the population manifests these symptoms, particularly urticaria, at some time during life.
Definitions
Urticaria (or hives) is an intensely itchy rash consisting of a raised, irregularly shaped wheal with a blanched center surrounded by a red flare. Urticaria is caused by histamine release from the mast cells of the dermis. Although chemical and physical agents such as detergents or ultraviolet light can release histamine from mast cells, histamine release is most commonly due to an immunologic reaction between antigens and IgE antibodies bound to the membranes of mast cells. The release of histamine-containing granules from mast cells is calcium-dependent and requires energy. In addition to histamine, other mediators, such as leukotrienes, prostaglandins, and platelet activating factor, also are released from immunologically stimulated mast cells. The binding of histamine to H1 receptors causes smooth muscle contraction and increased vascular permeability.
Angioedema is an area of circumscribed swelling of any part of the body.
