that the patient is having an anaphylactic reaction [3]. Anaphylaxis is a severe hypersensitivity reaction that can cause fatality [3, 9–16].
Anaphylaxis may be mediated through immunoglobu-lin E (IgE) or alternate pathways, including IgG, immu-noglobulin M (IgM), and complement system activation [13, 15, 16]. There are also non‐immunologic causes of anaphylaxis, such as thermal extremes [13, 15, 16].
This chapter will focus on IgE‐mediated anaphylaxis.
This type of anaphylaxis relies upon histamine as a pri-mary mediator [13]. Histamine is stored within certain cells of the body, mast cells. Mast cells are one of many components of normal connective tissue [17]. In the dog, mast cells are found in greatest numbers in the skin, lung, gut, and liver [18, 19].
Mast cells participate in inflammatory, immune, and neuroimmune responses [13]. When mast cells are acti-vated during an anaphylactic reaction, they rapidly release mediators, including histamine. The release of histamine from mast cells increases vascular permeabil-ity [13]. This leakiness of capillaries contributes to edema, a cardinal sign of inflammation [13].
In addition to histamine, mast cell granules also contain heparin, proteases, and proteoglycans [13]. These media-tors potentiate the body’s inflammatory response [13].
The subsequent activation of phospholipase A magni-fies inflammation through the creation of prostaglandin D2 and leukotrienes (LTB4, LTC4, LTD4, and LTE4) [13, 20–26]. Furthermore, the release of cytokines IL‐4, IL‐5, IL‐6, IL‐8, IL‐9, IL‐13, and IL‐33, and tumor necrosis factor (TNF‐α) contribute to shock [13, 27, 28].
Eighty percent of human patients who experience ana-phylaxis demonstrate cutaneous signs such as urticaria [3, 9, 11, 29]. According to a 2017 study by Rostaher et al., 67% of dogs with anaphylaxis develop wheals;
70.8% develop angioedema; and 37.5% develop both [3].
In addition, because the liver is the major shock organ for dogs, many canine patients develop vomiting and diarrhea [3, 30–36].
11 Erythematous Wheals and Angioedema
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