Cookie, an approximately 1.5-year-old female spayed Labrador retriever and her owner came for a veterinary dermatology consult after battling ear infections for almost a year. The owner, understandably, was frustrated. Cookie was miserable when her ears flared up, and every time the owner thought things were going well, another ear infection occurred.

An ear infection, or otitis externa, is a common reason for clients to bring their dog to the veterinarian. When treating this, it is helpful to consider the primary, secondary, predisposing, and perpetuating causes (PSPP) classification system in your approach.^1,2

Primary diseases, such as allergic dermatitis or hormonal diseases, lead to secondary infections with bacteria, yeast, or both. Over time, the chronic inflammation from otitis externa can lead to perpetuating factors, such as glandular hyperplasia, edema and stenosis of the canal, or biofilm production from bacteria or yeast.

Predisposing factors, such as excessive ear hair, moisture in the canals, or abnormal conformation, can put animals with primary diseases at a higher risk for more frequent and severe infections, but do not necessarily trigger infections alone.

While many owners bring their dog in once the secondary infection has caused noticeable discomfort, if the secondary infection is the only aspect of the disease addressed, then the owner will quickly be back into the office when the primary disease–an allergy in this case–causes the secondary infection to relapse.

What causes otitis externa?

Allergic dermatitis is a frequent primary cause of otitis externa.³ The three main triggers of allergic dermatitis are insects (fleas, mosquitoes, flies), foods (primarily proteins), and environmental allergens (weeds, grasses, tree pollens, molds, storage and dust mites, and dander from other species).

Parasiticides should be considered in any dog with allergic dermatitis, as up to 80 percent of dogs with environmental allergies are hypersensitive to proteins in flea saliva.⁴ Given environmental allergies are a diagnosis of exclusion, it is important to determine how much of a role canine adverse food reactions (CAFR) are playing before diagnosing an animal with atopic dermatitis. With so much confusion surrounding the diagnosis of CAFR, making evidence-based recommendations will help improve clinical outcomes.

Clinical signs of CAFR can begin at any age, and up to 40 percent of affected dogs will develop signs within the first 12 months of life.⁴ Cutaneous manifestations of CAFR can include pruritus, most often affecting the face, ears, paws, ventrum, and perianal skin, and secondary infections with bacteria and yeast in these areas. Other concurrent clinical signs may include vomiting and diarrhea, conjunctivitis, anaphylaxis, sneezing, and increased frequency of defecation.⁵

While serum testing for IgE and IgG levels against common foods are available through many reference laboratories, these serum tests have shown low repeatability and the accuracy is highly variable in dogs.⁶ In addition, CAFRs are frequently not mediated by IgE, therefore, serum testing evaluating IgE levels would be irrelevant.

Serum testing for CAFR should be avoided as a diagnostic approach, even if the owner asks for it, as the results are not useful and will only serve to confuse the owner’s approach to and assessment of their pet. An elimination diet trial followed by provocative challenge feeding remains our best diagnostic tool at this time.

Elimination diet trial

Eliminating common allergens from the diet is crucial for success of a diet trial. Beef, dairy, chicken, wheat, and lamb are the most common allergens identified in dogs with CAFR. Less common allergens include soy, corn, egg, pork, fish, and rice.⁷ “Cutting out chicken” is a common first step owners may attempt at home to try and eliminate what they perceive as a potential food trigger.

Many OTC commercial diets are marketed as “single protein” or “limited ingredient.” When single protein or limited ingredient diets were evaluated across 17 different research studies, up to 83 percent of diets tested contained ingredients not listed on the label.⁸ Up to 38 percent of diets had ingredients listed that researchers were unable to identify within the food.⁸ Clients should be cautioned about the risk of OTC diets causing ongoing disease if an animal is reacting to a contaminant ingredient.

Prescription novel protein diets are unlikely to have contaminant proteins present in the food. Cross reactivity can occur between proteins with similar structures within a protein group, such as ruminants (beef, dairy, buffalo, and venison), poultry (chicken, turkey, egg, and duck), as well as different fish species.^9-11 While these diets may offer more variety and palatability, prescription novel protein diets are best used for long-term maintenance feeding in dogs with confirmed CAFR, rather than for obtaining an initial diagnosis. The risk of cross reactivity and ongoing clinical signs may make it appear as if an animal has continued disease from environmental triggers, when, in fact, they are continuing to react to proteins in the diet. If a dog is not thrilled with the way a hydrolyzed protein diet tastes, novel protein diets offer an alternative that may help some owners get on board with the treatment plan for long-term management of CAFR.

Small protein fragments are less likely to trigger an immunologic reaction than intact proteins. Hydrolyzed diets contain short amino acid chains (<10kDa) that prevent successful antibody cross linking for a hypersensitivity reaction to occur. These diets can reduce or eliminate clinical signs of food allergies. Reactions can occur if the diet is only partially hydrolyzed, as has been noted in some hydrolyzed chicken and soy protein diets.^12-15 Since soy is an uncommon allergen in CAFR, this is less of a concern than a partially hydrolyzed chicken diet, as many more dogs with reactions to chicken would be at risk for disease progression.

Results

Offering dogs a variety of potential diets during the exam in the office will decrease a pet’s anxiety level, determine the dog’s preference for a particular food, and demonstrate the food’s palatability to the client.

Many pet owners have pre-formed opinions on pet nutrition that should be acknowledged and considered. Having an open conversation about the common pitfalls of elimination diet trials and asking the owner about their personal circumstances will help to avoid mistakes that interfere with interpretation of the pet’s response to the diet trial. All other foods should be eliminated during the next eight weeks. Oral parasiticides may need to be switched to topicals to avoid protein exposure during this time.

Asking about chew toys, treats, toothpaste, bones, and how oral medications are administered will allow the veterinary team to offer solutions to eliminate continued allergen exposure during this diagnostic test the owner is performing for you at home. Educational resources, including podcasts and handouts, can help the owner understand the goals and requirements of a good elimination diet trial.

By five weeks into the elimination diet, 80 percent of dogs with CAFR will have remission of skin lesions. Gastrointestinal signs may resolve more quickly. If gastrointestinal signs worsen within the first two weeks, an alternative diet should be selected.

Ninety percent of dogs with CAFR will have remission by eight weeks.¹⁶ At this point, next steps should be discussed with the owners. If there is evidence of ongoing skin and ear disease, a workup of environmental triggers with allergy testing and implementing immunotherapy with a dermatologist should be considered.¹⁷

If the clinical signs have resolved, the owners can consider a provocative challenge feeding with the original diet to confirm the diagnosis of CAFR. This feeding results in relapse of clinical signs by day five in 50 percent of dogs, and by day 14 in 90 percent of dogs.¹⁸ Alternatively, owners can be instructed on transitioning to a prescription novel protein and monitoring for a reaction if the pet does not find the hydrolyzed diet highly palatable. If the dog is happy with the prescription hydrolyzed protein diet, owners can be instructed on how to perform individual protein challenges to determine which ones will and will not trigger reactions. These individual challenges are best performed in dogs whose reactions are easy to recognize and resolve.

Cookie’s secondary infection was treated with topical antimicrobials based on cytology. In addition, she was given a short course of oral glucocorticoids to reduce inflammation and edema within the ear canals. The owner was instructed on the importance of maintenance cleaning, as well as cleaning techniques, to address increased cerumen production as a perpetuating factor. After completing an eight-week elimination diet trial, Cookie’s clinical signs had completely resolved. The owner’s goal was to find high value rewards he could use for agility training to help channel her Labrador enthusiasm and energy. The owner performed individual ingredient challenges with several proteins, one at a time, and addressed any flare ups quickly before her ears ever become a problem again.

By teaching owners about CAFR using engaging education tools, you can implement satisfying diet trials into your workup of allergic dermatitis.

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Brittany Lancellotti, DVM, DACVD, is a veterinary dermatologist at Veterinary Skin and Ear in Los Angeles, Calif., and a graduate of Western University of Health Sciences. Dr. Lancellotti is the founder and host of ‘Your Vet Wants You to Know,’ an edutainment podcast designed to improve pet owner knowledge, veterinarian efficiency, and treatment outcomes. Lancellotti is a Fear Free certified professional and focuses her practice on decreasing stress in her patients, clients, and colleagues.

References

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