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Cutaneous Adverse Food Reactions

Ralf S. Mueller, Dr. Med.Vet., DACVD, FANZCVSc

Centre for Clinical Veterinary Medicine, Ludwig‐Maximilians‐University of Munich, Munich, Germany

Etiology/Pathophysiology wheat – ingredients that are most commonly present in
commercial dog foods (Table 161.1). In the cat, beef,
Cutaneous adverse food reactions include any skin reac- dairy, fish, and chicken are the most common reported
tions that are reproducible. Most commonly seen is pru- offending antigens (see Table 161.1).
ritus, but recurrent pyoderma or edema have also been To what degree related proteins can cause clinical
reported. Food allergy is an immunologically mediated problems via cross‐reactivity is not clear. One study eval-
reaction caused by food. Type I hypersensitivity medi- uating individual rechallenges in dogs with adverse food
ated by food‐specific IgE antibodies is the most common reactions could not demonstrate evidence of cross‐
reaction, but delayed type II (T cell mediated) and type reactivity between, for example, beef and cow’s milk.
III (where food‐specific antibodies and food antigens However, a case report of a dog with oral allergy syn-
form complexes) hypersensitivities may also occur. drome described cross‐reactivity with tomato and cedar
In veterinary practice, the immunologic basis of food pollen. A further in vitro study identified bovine IgG as a
reactions is rarely documented. Thus, technically, the com- major antigen in dogs and a potential source of cross‐
monly used term “food allergy” is inappropriate, because reactivity between beef, cow’s milk and potentially mut-
adverse food reactions may also be nonimmunologically ton (as there is a high homology between bovine and
induced (and are then called food intolerances). Food intol- ovine IgG), but whether this is clinically relevant has not
erance may be pharmacologic, such as those mediated by been demonstrated convincingly at this point.
pharmacologically active ingredients of the diet (e.g., hista-
mine), toxic (caused by toxins in the food commonly pro-
duced by microorganisms in contaminated food stuffs), or History and Clinical Signs
metabolic (ingredients in the food are metabolized in the
patient to a substance causing the reaction). If none of those Adverse food reaction is characterized in most cases by a
mechanisms can be identified, the reaction is idiosyncratic. pruritic and nonseasonal dermatitis. The face, feet, ven-
However, proving the exact pathogenesis in an indi- trum, and perianal area are often affected in the dog
vidual patient in practice is very difficult. Serum IgE test- (Figure 161.1). Otitis externa is common and may be the
ing for food‐specific antibodies in normal dogs without only presenting sign in some dogs (Figure 161.2).
clinical problems is characterized by a high number of The skin may be erythematous; self‐trauma quickly
false‐positive reactions and reliable tests for other types leads to alopecia and excoriation and in chronic cases
of adverse food reactions are lacking. Thus, in most cases lichenification of affected skin (Figure 161.3).
the diagnosis of adverse food reaction is made by Papules, pustules, and oily and scaly skin may be due to
response to an elimination diet and deterioration on common secondary infections with bacteria and/or yeast
rechallenge, as described below. organisms. Concurrent gastrointestinal signs are seen in
In human medicine, food allergens are typically glyco- up to 25% of affected dogs. Beyond vomiting and diar-
proteins with molecular weights between 10 and 70 kDa rhea, gastrointestinal signs may include frequent defeca-
and some typical allergens come from nuts, shellfish, tion, borborygmi and flatulence, which may in some
milk, and eggs. In dogs, the most commonly identified dogs be the only noncutaneous clinical signs. Recurrent
food antigens are beef, dairy products, chicken, soy, and bacterial infection and vasculitis were also reported in

Clinical Small Animal Internal Medicine Volume II, First Edition. Edited by David S. Bruyette.
© 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/bruyette/clinical