Pruritus associated with food allergy can result in significant facial trauma due to self-excoriation.Photo courtesy Casey Stepnik While cats suffer similar allergic skin diseases as dogs, the manifestation and management of these conditions do not always mirror that of their canine counterparts. From grooming behaviors to feeding preferences to different nutritional requirements, cats with allergic skin disease can present obstacles not usually encountered in dogs. Additionally, diagnosing and managing food allergies in cats also present unique challenges of their own. Just as in dogs, cats experience three primary categories of allergic skin disease. These include flea bite hypersensitivity (or flea allergy dermatitis [FAD]), food-induced hypersensitivity dermatitis (i.e. adverse food reaction [AFR]), and non-flea, non-food induced hypersensitivity dermatitis (NFNFIHD).1-4 The latter is similar to atopic dermatitis (AD) in dogs, but since pathogenesis of this disease is not yet clearly understood, including the role of immunoglobulin E (IgE), it has also been referred to as “feline atopy-like syndrome.”2,3,5 Keep in mind these cats can also have concurrent hypersensitivities to food and flea bites. Making the diagnosis Before embarking on an elimination diet trial, it is imperative to rule out other causes of pruritic skin disease, including parasites and infections, which can be done at the first visit through skin scrapings, cytology, and dermatophyte polymerase chain reaction (PCR). In more severe cases, autoimmune skin disease should also be considered. Flea bite hypersensitivity is the most common cause of allergic skin disease in cats in most areas of North America, especially in regions where fleas are endemic.1,2,5 While diagnosing FAD is fairly straightforward in dogs, it may be less so for our feline patients. Many cats live indoors, which can lead owners to assume flea infestation is not possible. In reality, fleas can easily be brought in by outdoor and visiting pets, as well as on clothing and shoes. In addition, because cats are highly fastidious groomers, even examination by a veterinarian may reveal no evidence of fleas or flea dirt on cats with FAD. While FAD is usually the easiest allergic skin disease to manage, the news a cat may have fleas is rarely what owners want to hear. Further, they may become defensive because they believe the diagnosis implies they are not taking proper care of their pet. Quite the contrary, even when an over-the-counter flea preventative is being used and no fleas (or flea dirt) are found on the patient, FAD should still be considered. Cats don’t have to be flea-infested to be symptomatic—a single flea can bite a cat multiple times an hour; it may only take a few bites to cause a reaction in a highly sensitized cat. It is always worth trying a fast-working topical (e.g. selamectin, dinotefuran/pyriproxyfen, fluralaner) or oral flea preventative (e.g. spinosad, daily nitenpyram) for two to four weeks to see if there is improvement. If there is, that treatment should be continued every three to four weeks, year-round. Environmental allergies to pollens, trees, grasses, mold, and dust mites are another cause of allergic skin disease. In younger cats (less than three years of age) whose outbreaks are seasonal and in which flea allergy has been ruled out, NFNFIHD is highly likely and it may not be necessary to do an elimination diet trial to make the diagnosis. Some cats may present with localized (head and neck most commonly) and generalized pruritus/miliary dermatitis, as well as allergic otitis, eosinophilic complex, and, more rarely, nasal discharge or sneezing.1 Treatment alternatives for NFNFIHD in cats are similar to those used in canine atopic dermatitis, with options including steroids, antihistamines, cyclosporine, and oclacitinib, the latter of which is extra-label in cats. Vaccine desensitization can also be considered. Nutritionally, administration of omega-3 fatty acid supplements may help decrease inflammation. A process of elimination Chronic, year-round pruritus and skin inflammation typifies AFR in cats. As with NFNFIHD, this allergic disease can result in significant facial, head, and neck trauma, although lesions are also found elsewhere, such as the ventral abdomen and ears. It is always important to examine the abdominal area and do an otoscopic evaluation as part of any good wellness physical examination to ensure allergic patients are not being missed. Eosinophilic diseases can also occur in AFR.1 Concurrent gastrointestinal signs, such as vomiting and/or diarrhea, may occur in up to one-third or more of cats with ARF1,4,6 and should raise a clinician’s suspicion for reaction to food as the cause of the skin disease. Accurate diagnosis of AFR in cats, like dogs, requires feeding an elimination diet for eight to 14 weeks. As with dogs, the choice of elimination diets includes novel protein, as well as hydrolyzed and home-cooked diets. Each has pros and cons. Unless the owner is already successfully feeding a home-cooked diet, cats are less likely than dogs to take to one. Veterinarians should always recommend clients consult a veterinary nutritionist to formulate a home-prepared diet. In cats, this is true even for diet trials of short duration. Cats are a more nutritionally demanding species than dogs and require higher total dietary protein, specific amino acids (arginine and taurine), fatty acids (arachidonic acid), and preformed vitamin A, vitamin D, and niacin. Novel protein hypoallergenic diets are formulated with protein sources that are less commonly associated with AFR. Rabbit, venison, and duck are three of the more popular ones used in these diets. Importantly, novel protein diets are palatable for many cats, and are widely available in canned formulations. The disadvantage of this approach is a growing lack of truly novel protein options for patients. In their desperation to find a solution, many owners have already tried a host of different OTC diets before coming to the veterinary office for help. For this reason, it is essential to take a thorough diet history prior to selecting a novel protein diet. This includes all diets fed for the lifetime of the pet, as well as treats, supplements, flavored medications, and any human food offered. It is very difficult to use these diets in cats whose diet history is unknown. Hydrolyzed diets are formulated with proteins that have been broken down via a process using water (hydrolysis) into small enough pieces that the immune system no longer reacts to them. Like novel protein diets, hydrolyzed formulas are available as both dry and wet food. One benefit of hydrolyzed diets is their viability for the vast majority of cats, regardless of diet history. Another is these diets tend to be highly digestible, which is especially important for a cat that also has GI disease. On the downside, palatability, particularly with some of the canned diets, can be a problem for some cats. Additionally, it is possible some highly sensitized animals could still react to protein hydrolysates. When selecting an elimination diet, veterinarians should not view the protein source as the only factor. Another important consideration is the carbohydrate source. A highly digestible carbohydrate source is important for many patients, due to the frequency of GI problems associated with food allergy. In addition, some carbohydrate sources, such as oats and green pea, contain enough protein to trigger reactions in sensitized animals. Diets formulated with a single, low-allergen carbohydrate source, such as rice starch, may be preferable. Finally, while veterinarians may find an elimination diet that is their “go-to” option for diagnosing AFR in cats, there is no guarantee any one diet will work for every case. If an elimination diet does not work for a patient—yet the practitioner remains highly suspicious of food allergy—it may be necessary to conduct a second food trial with a different diet. This is particularly a consideration for patients that are not steroid-responsive or that suffer from concurrent gastrointestinal disease. Confirming the diagnosis The only way to definitively diagnosis AFR is to conduct a dietary challenge following a successful diet trial. Other factors, such as waning of environmental allergens during the same time period, may influence the perceived response. A dietary challenge can either introduce a succession of non-novel proteins or slowly reintroduce the cat’s previous diet. Either way, the patient should be monitored for a recurrence that can occur within minutes—or within several weeks. While confirming the diagnosis is always preferred, on a real-world level, it is often the case that clients do not want to risk their cat becoming pruritic again. With these patients, it may be best to keep the cat on the elimination diet, provided it is complete and balanced for the life stage. Food allergy in cats can be miserable for the patient and owner. Although diagnosis of AFR can be challenging and time-consuming, once the condition is identified, lifelong control of clinical signs can be achieved with dietary management. References Miller W, Griffin C, Campbell K. 2013. Small Animal Dermatology. Elsevier Mosby. Chapter 8; 363-431. Gedon M, Mueller R. Atopic Dermatitis in dogs and cats: a difficult disease for animals and owners. Clin Transl Allergy. 2018 8(41). Diesel A. Cutaneous Hypersensitivity Dermatoses in the Feline Patient: A Review of Allergic Skin Disease in Cats. Vet. Sci. 2017 Jun; 4(2): 25. Guilford WG, Markwell PJ, Jones BR et al. Prevalence and causes of food sensitivity in cats with chronic pruritus, vomiting, or diarrhea. J Nutr. 1998;128:2790S–2791S. Bajwa J. Atopic dermatitis in cats. Can Vet J. 2018 Mar 59; 311-313. Guilford WG, Jones BR, Markwell PJ et al. Food sensitivity in cats with chronic idiopathic gastrointestinal problems. J Vet Intern Med. 2001; 15; 7-13 Emily Cross, DVM, DABVP (canine/feline), is director, professional resources group, for Purina Institute. She is also in clinical practice as an associate veterinarian at Kearny Mesa Veterinary Center in San Diego, Calif.
