Cutaneous adverse food reactions

Pixel-Shot/Adobe Stock

During her session, “The Itchy and Scratchy Show: How to Confidently Diagnose Canine Allergies,” presented at Fetch Coastal dvm360 Conference in Atlantic City, New Jersey, Julia E. Miller, DVM, DACVD, emphasized the importance of including allergic dermatitis in the differential list when presented with a pruritic dog. In the first half of her 2-part lecture, Miller taught attendees how to diagnose patients that present with allergies, in a step-by-step, checklist-based manner.

Miller shares that, while a presenting case of allergies is more than likely atopy, food allergies are responsible for 10-25% of allergic dermatitis cases. Allergic dermatitis is a diagnosis of exclusion, which requires the careful ruling out of other pruritic conditions. Once alternatives including ectoparasites, flea allergy dermatitis (FAD), neoplasia, and secondary microbial infections have been ruled out, food allergies should be considered. Food allergies are nonseasonal, and many dogs become sensitive to what they are used to, so a food change is not a prerequisite for diagnosis.

Cutaneous adverse food reaction (CFAR) is an adverse immunologic reaction to an allergen in the diet. Miller warns that the diagnosis of CFAR could be difficult, as the clinical picture is often identical to environmental allergies (atopic dermatitis). The only accurate diagnostic test that Miller advises is a strict, prescription diet trial.

“So, you’ve got your itchy dog, you’ve ruled out your ectoparasites, you’ve done an incredibly throughout derm [physical exam], you’ve done cytology… you’ve ruled out all of those secondary things, but you still have this non-seasonally itchy dog… you think you want to go with a food allergy, just to see what we’ve got going on,” Miller, said during her presentation. “So, ‘how do we diagnose a food allergy?’ It’s a prescription diet trial. That’s the only way to diagnose a food allergy. Period, end of story.”

The following should be avoided while conducting a prescription diet trial—Miller recommends adding these to a handout for owners:

• Over-the-counter treats
• Meal toppers
• Flavored pill pockets, capsules, pills
• Flavored toys
• Flavored flea, tick, and heartworm preventatives
• Ingesting cat food, litter, or vomit

Throughout the course of a diet trial, patients will likely require antipruritics for 3-6 weeks. Miller recommends Apoquel, glucocorticoids, and Cytopoint. All secondary infections should be cleared prior to the trial. She advises that diarrhea often clears up before pruritus.

After 3 weeks on the diet, more than 50% of patients will show marked improvement. That number increases to 85% at 5 weeks, and 95% at 8 weeks. Most cases do not require 3 months, and trials should not last longer than 4-6 weeks with no signs of improvement. If a patient does not react, and food can be ruled out along with all other causes of pruritus, it can be concluded that it’s atopy.

Recommended diet trials

The options for prescription diet trials are commercial novel protein, hydrolyzed protein, or home-cooked meals. Proteins are the most common allergens, including chicken, beef, lamb, or fish, although any carbohydrate or fat could also be an allergen. There are no perfect diets that fit all patients, and it’s important to consider the patient’s diet history, appetite, and owner requirements.

It’s crucial to know which proteins are considered novel to a patient. There is also the potential for cross reactions between protein sources with close taxonomic relationships. Miller clarified that, if a patient is allergic to chicken, turkey and duck are not novel proteins. If a patient is allergic to beef, venison or lamb are not novel. Hydrolyzed proteins involve disrupting the protein structure, thereby removing any existing allergens within a patient’s diet. Some dogs with CAFR will still react to diets containing hydrolyzed versions of the food. Several novel protein diets including rabbit, fish, venison, kangaroo, black fly larvae, and more.

Miller recommends several commercial diets, including:

• Purina Pro Plan Veterinary Diets HA with hydrolyzed soy and corn starch +/- hydrolyzed chicken or salmon
• Royal Canin Veterinary Diet Hydrolyzed Protein (HP) with brewers rice, hydrolyzed soy protein and chicken fat
• Ultamino with corn starch and hydrolyzed poultry-by-products aggregate (chicken feather)
• Hill’s Prescription Diet z/d with brewers rice and hydrolyzed chicken liver
• Blue Natural Veterinary Diet HF with hydrolyzed salmon, pea starch, and potatoes
• Purina Pro Plan EL Elemental, with purified amino acids with corn starch and tapioca starch

Allergy tests to avoid

Miller emphasized that [serum] food allergy tests are not clinically proven, and she does not trust them, she explains that intradermal allergy testing is ineffective and shared a story about saliva and hair allergy testing being completely fabricated. Meanwhile, over the counter diet trials are unreliable due to reasons dealing with cross contamination.

“They’ve done studies that show that there’s actually quite a bit of chicken in these [chicken-free dog foods] because they’re made on the same [food] lines,” Miller said. “So, over the counter diets are never a true diet trial, ever. Period. End of story.”

Reference

Miller J. The Itchy and Scratchy Show: How to Confidently Diagnose Canine Allergies. Presented at: Fetch dvm360 Conference; October 14-16, 2024; Atlantic City, NJ.