Valerie A. Fadok, DVM, PhD, DACVD
The skin is a reflection of general health, and skin and coat quality can be reduced by a number of diseases affecting the general wellbeing of our pets. There are a number of diseases affecting the skin specifically that can be improved by optimal nutrition using premium quality diets. In addition, we see conditions in which specific nutrients are used at pharmacologic levels to resolve clinical signs. In this seminar, we will briefly review the specific diseases in which nutrients are part of specific therapy, but we will focus most of our time on 2 allergic diseases in which dietary intervention is a specific part of the treatment plan: canine atopic dermatitis and food allergy.
Diseases in Which Specific Nutrients Are Used
Vitamin A Responsive Dermatosis in Spaniels
Cocker Spaniels and other spaniels are prone to seborrheic skin disorders. In a subset of these dogs with focal erythematous plaques associated with follicular casting, response to supraphysiologic doses of vitamin A is seen. This is an adult onset disease with a ventral distribution and the lesions can be mistaken for pyoderma or can be complicated by pyoderma. Vitamin A is given at a dose of 800–1000 IU/kg daily. Primary seborrhea does not respond to this approach, but it has responded to synthetic retinoids such as etretinate or acitretin. These medications are difficult for veterinarians to obtain in some countries, and are quite expensive; they are not widely used at this time.
Zinc Responsive Dermatosis
Zinc responsive dermatosis syndrome I is found primarily in Nordic breeds; in the vast majority of cases these dog are on a balanced diet so they are not deficient. Recently this syndrome was identified in a severe form in a litter of Pharaoh Hounds. The disease is believed to be hereditary, but the exact pathogenesis is not well understood. It is suspected that they may not absorb zinc properly. They present with focal erythematous patches and plaques covered with thick yellow crusts; these lesions are often present on the face and pressure points. In some dogs, gastrointestinal disease can exacerbate the syndrome. Histopathologic findings include diffuse parakeratosis on the skin and in the hair follicles. Zinc supplementation is recommended for life, and secondary infections should be addressed. Zinc methionine is given at 1.7 mg/kg/day and is preferred for its increased bioavailability. Zinc gluconate can be given at 5 mg/kg/day and zinc sulfate at 5–10 mg/kg/day. For dogs who do not respond to oral administration, intravenous zinc administration has been recommended, but needs to be used with caution to avoid cardiac arrhythmias. Zinc sulfate is administered slowly at 10–15 mg/kg prn. Syndrome 2 can be seen in any breed and is associated with a poor quality diet high in phytates which bind zinc in the GI tract. Zinc supplementation can be used initially, but the ultimate goal is to put these dogs on a better quality diet.
Superficial Necrolytic Dermatosis/Hepatocutaneous Syndrome
This painful, erosive, and crusting disease is associated with multiple underlying causes, which include glucagon-producing tumors, diabetes mellitus, and hepatic disease. The latter is characterized by a "Swiss cheese" appearance to the liver on ultrasound. These patients appear to have low amino acid levels in their blood. Treatment with intravenous amino acids (10% Aminosyn, 1 cc/24 kg) once to twice daily can provide improvement for some patients; if they have not responded within 4 weeks, the prognosis is poor. Many patients can live for a substantial period of time with this treatment, and with dietary manipulations. Most advocate for a high protein diet with supplements such as eggs (1 per 5 kg per day) and amino acid powders orally. In addition, some investigators have advocated for supplementation with zinc, vitamin E, and fatty acids as well.
Management of Canine Atopic Dermatitis
Canine atopic dermatitis is a chronic inflammatory disease which tends to progress over time. Two major factors contribute to the severity of the disease: the genetic background of the dog and the environment in which he/she lives. Genetic factors contribute to the impaired skin barrier observed in atopic dogs and the immune response skewed toward the T helper 2 pathways. Allergens gain access to the immune system by absorption through the skin. Repetitive infections with staphylococcal and yeast infections are often associated with increased severity.
Making the Diagnosis
Honing in on a diagnosis of atopic dermatitis is based on appropriate history (breeds of predisposition, age of onset) and distribution of clinical signs (usually on sparsely haired areas on the face, ears, feet, and ventrum). Ruling out ectoparasites, treating infections, and considering food allergy are critical. Allergy testing (intradermal skin testing and/or serum allergy testing) are used to select allergens for immunotherapy.
A multimodal approach to treating this disease is essential to success. The first step is to avoid any allergens that can be avoided; practically speaking these are food triggers and ectoparasites such as fleas. The second step is to utilize allergen specific immunotherapy to change the immune response; this is the only biologic treatment for the disease and the only treatment that actually modifies the disease and prevents progression. Immunotherapy can be delivered by injection or by sublingual drops. The third step is treatment of infections, utilizing bathing and systemic antimicrobials when necessary. The fourth step is to repair the skin barrier, utilizing optimal nutrition, oral fatty acids, and topical lipids (ceramide complex, phytosphingosine, essential fatty acids in refined essential oils of herbs and grains). The fifth step is to control itch and inflammation.
Nutritional Support for Atopic Dogs
A small number of papers support the notion that itch and inflammation in atopic dogs can be reduced when dogs are fed a premium diet containing fatty acids with optimal omega 6:omega 3 fatty acids. Itch and CADESI scores (measure of inflammation in the skin) were reduced over time.
Diagnosis and Management of Food Allergy
The pathogenesis of food allergy in pets is poorly understood. The skewed T helper 2 response, associated with IgE production, may be present in in some patients, but in others different immunologic pathways may be more predominant. Because the natural state for the gut is to induce tolerance to food components, factors such as genetics and environmental triggers (viral infections, intestinal parasites) may contribute to a break in tolerance. The true prevalence of pure food allergy is also not known, but it is clear that food triggers can play a role in atopic dermatitis.
Making the Diagnosis
A history suggestive for food allergy is the combination of pruritic inflammatory skin disease and gastrointestinal signs, but food allergic animals can have either skin disease or gastrointestinal disease. Recurrent otitis externa and recurrent inflammatory anal sacculitis are also suggestive. Dermatologic syndromes can include "ears and rears" with itchy ears and anal skin, a pruritic skin disease that is distributed on the caudal half of the body (mimicking flea allergy) or a more generalized syndrome resembling atopic dermatitis. A number of laboratory tests have been suggested as useful for the diagnosis of food allergy; these are not supported by rigorous evaluation. The gold standard for diagnosis of food allergy is the diet trial followed by challenge. Much is unclear with regard to the proper food trial, including choice of diets, the duration of the diet, and the proper way to perform the challenges. What is clear is that the whole family has to agree to participate if we are to achieve success.
Choice of Diets
The choice of diets must be based on a complete diet history, which can be difficult to get! We need to consider the main diet and the treats, but also who feeds the dog, whether table scraps are given, whether flavored medications are used, and whether toys such as rawhides or pig ears are given. For animals that spend time outdoors, strict food trials can be difficult, if they like to hunt. Most clinicians advocate for a novel protein diet, because hydrolyzed proteins are not effective for all animals allergic to the protein used in these diets. Novel proteins in commercial diets are becoming difficult to find. Many of the ingredients considered novel a few years ago are now present in over-the-counter diets, but these diets are not as stringently prepared and may not work for diet trials. Home cooked diets have become more popular in some parts of the world; it is best that these diets be balanced by a nutritionist.
Duration of Diet Trial
Recommendations for duration vary considerably, with some clinicians advocating for 12 weeks or more. My belief is that if the clinical signs are due to food allergy, some improvement should be seen within 8 weeks. If there is no improvement within this time, it is reasonable to stop the trial. Because these dogs are quite itchy, we can put them on glucocorticoids or oclacitinib for the first 6 weeks. We then stop the drug and continue the diet. If the pruritus comes back within 48 h, food allergy is much less likely and we consider atopic dermatitis. If the itch is resolved, we can move forward with food challenges.
The first food challenge is to feed the old diet. We mix the old diet with the test diet 1:4 and feed for 5–7 days. If there is no increase in itch, then food allergy is less likely and any improvement seen is likely due to other environmental triggers. Some clinicians believe that it may take up to 14 days to see a response, so they advocate for longer challenges. Once we see the relapse with the old diet, we can recommend single ingredient challenges to develop a list of foods to avoid. Most animals are reactive to animal proteins, so we recommend using chicken, beef, pork, lamb, fish, egg, milk as challenges. Some animals may be reactive to vegetable proteins, so we often challenge with soy, wheat, corn, rice, potatoes. The key is to focus on the foods which the animal has eaten before.
Avoidance is the best treatment for any allergy and uniquely suited to the food allergic patient. It is important to keep in mind that pure food allergies may not be common, and that food allergy is often a component of atopic dermatitis. If residual itch is present after elimination of food triggers then we should move forward with a workup for atopic dermatitis.
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