Atopy diagnosis time consuming for DVMs and owners

Atopy or inhalant allergy in the cat is probably underdiagnosed because of cats' ability to respond so well to steroids.

However, as we all know with repeated steroid use in the cat, diabetes mellitus is a dangerous consequence. Recent reports of steroid-induced cardiomyopathy are also of serious concern. With the most common inhalant allergen in the cat being dust mites — a year round problem — it is not advisable to maintain the patient on continuous steroid therapy particularly when other therapies for allergy are available.

Photo 1: This cat is suffering from inhalant allergy with preauricular erythema and allergic otitis.

We have all recognized atopic cats in our practices, but, scientifically, atopy has yet to be proven in cats. To date, feline IgE has not been isolated and identified. However the presence of a reaginic antibody has been demonstrated via passive cutaneous anaphylaxis (PCA) in healthy cats injected with serum from atopic cats. The molecular weight of this feline reaginic antibody is similar to IgE in other species and feline "IgE" cross reacts with canine IgE, all alluding to the existence of feline IgE.

Looking for signs

Clinical signs and symptoms of atopy in cats can vary greatly compared to atopic symptoms in dogs. Some effected cats show parallel symptoms of atopy in dogs with face rubbing, rectal itching and foot licking/biting. Others present with symmetrical alopecia of the trunk and hocks, and just general excessive grooming. Recurrent otitis, eosinophilic granuloma complex lesions including rodent ulcers and "pouty chins," miliary dermatitis and chin acne can all be symptoms of feline atopy. In our practice, most cats effected are young or middle-aged, and the majority have "orange" in their color (either calicos or orange tabby's). Age of onset can be difficult since many cats are adopted at an unknown age or live outside for awhile then are brought inside and become allergic.

Unless there has been a significant change in the patient's environment, we usually do not see atopy in elderly cats. Probably the most common purebred cat we see with atopy is the Devon Rex, and symptoms usually present at a young age.

Photo 2: Note the chin acne in this atopic cat. Atopy is an important differential in feline acne.

Perhaps the most difficult aspect of treating atopy in the cat is, in fact, determining that the cat is atopic.

Many of the differentials of atopy in the cat are steroid responsive which is the reason steroids tend to be used so much in this species.

However as scientists, we have the ability to use laboratory diagnostics, including skin scrapings, cultures or blood tests, to rule in or rule out differential diagnoses.

When to inject?

It certainly requires less time to administer a steroid injection to a pruritic cat, but are we truly doing that patient justice? Before arriving at the diagnosis of atopy, which truly is a disease of exclusion, we need to rule out several other differentials including ectoparasites (fleas, Cheyletiella mites, demodex gatoi, Notoedres), dermatophytosis, food allergy, pemphigus foliaceus, bacterial pyoderma (somewhat rare in the cat) and Malassezia dermatitis.

Ruling out ectoparasites can be difficult, especially in a multi-cat household or in a household that fosters pets. Flea allergy in the cat does not present with a typical dorsal lumbar alopecia as in the dog, but it does a mixed bag of symptoms such as those mentioned previously. All the pets in the household need to be checked for fleas and treated with an adulticide product, and the household should be treated with an environmental spray.

Surprisingly, many owners resist the notion that their cats could be so pruritic "only from fleas". Other owners accept that "there are a few fleas here and there, but that's not what's causing his itching". (You know you have your work cut out for you when you hear those kinds of statements!)

Thankfully, we now have safer prescription flea products than those available in the past. Yet, every so often owners apply a potentially lethal dose of pyrethrins with an over-the-counter, dog-only product that is contraindicated in cats.

The teachable moment

As mundane as it may be to give the flea lecture one more time, I find it is still very necessary education, particularly because repetitive education, may occasionally hit home.

Cheyletiella seems to be on the rise, possibly because the "old" flea products kept it under control yet only a few of the newer adulticides will affect this mite. In our office, we find the mite on combings that sometimes require multiple combings viewed in oil under low power. The mite may involve asymptomatic carriers, so be sure to comb all the pets in the household especially those with any internal medicine disorders.

Photo 3: The ventral abdomen of a Devon Rex cat shows the reaction of dust mite allergies. There is secondary Malassezia present.

Cheyletiella seems to like immunocompromised individuals. This mite will occasionally bite humans so if the humans have papular lesions or complain of pruritus that should intensify your search on the cat. Cats with Cheyletiella will, as mentioned previously for atopy, present with the various symptoms of allergy in the cat that include face rubbing/excoriation, pruritic symmetrical alopecia, miliary dermatitis, sneezing and eosinophilic granuloma complex lesions.

Finding the mite can indeed be a problem since cats are such good groomers and many will ingest the mite. Occasionally the mite egg, which resembles a hookworm egg, will be found in a fecal exam.

Treatments include ivermectin (beware of idiosyncratic reactions including death in the cat), Revolution, Frontline Spray or lime sulfur dips along with treatment of the environment. Be sure to treat all the pets in the household even those without symptoms.

Demodex gatoi is a relatively newly described contagious parasite of the cat. When present, it can be found on combings or scrapings as the mite is located superficially. Treatments include lime sulfur dips every five to seven days. Be sure to check other cats in the household because the mite is contagious. Some cats with demodex gatoi may have underlying atopy, and the mite may have manifested due to steroid overuse.

Food allergy concerns

Food allergy should be suspected in any cat that has non-seasonal symptoms (same as dust mite allergic cats). Any age cat can be affected and this differential should be kept in mind when an older cat formerly not pruritic, becomes pruritic (Cheyletiella should also be considered). Unfortunately, there is no valid blood or skin test for food allergy, so the diagnosis can be made by feeding an elimination diet for at least four to six weeks. An elimination diet is one without any ingredients to which the cat has been exposed (i.e. no corn, wheat, egg, beef, chicken, soy, dairy or fish).

Photo 4: Flea allergy in this cat manifests as pruritus and alopecia over the dorsal lumbar area.

The foods that fit this category are prescription diets available through veterinarians. Examples include Innovative Veterinary Diets (duck/pea, rabbit/pea, venison/pea and lamb/pea—if the patient has not eaten lamb in the past) or Eukanuba lamb/barley. An over-the-counter lamb and rice diet is not considered an elimination diet because the majority of these foods contain other ingredients to which the cat has been exposed. Some cats are finicky eaters, and if they won't eat the diet they won't improve so it is important to try little tricks to get them to eat.

A few ideas include introducing the new food gradually combining it with the current diet at first, warming the food in the microwave, or pureeing it in the blender.

We also dispense what we call "kitty buffet" which consists of a small ziplock bag containing a small amount of each of the dry diets to see which the cat will prefer. We also dispense two cans each of the canned foods for the same reason.

There has been some discussion recently of food-storage mites and pets acquiring an allergy to these mites. Cats with a foodstorage mite allergy will improve on a canned only diet — a diet without any dry foods, cereals, grains or cheese. Skin testing, blood testing and just a canned diet trial for a month will help diagnose an allergy to food-storage mites. Some cats with food-storage mite allergy present with facial excoriation and recurrent otitis.

Considering differentials

Dermatophytosis is a differential for almost any cat skin disease. None of us probably do enough fungal cultures as dermatophytosis can have many different skin manifestations including no visible lesions! We use the Mackenzie toothbrush technique that involves using a new toothbrush to thoroughly comb the cat over a five-minute period, then implant the hairs into the fungal culture medium (we use DermDuet available through Bacti-Lab).

A Wood's light can be helpful but relying on that alone will allow you to miss dermatophytes that do not fluoresce (the majority of dermatophytes do not fluoresce). However, when using the Wood's light remember to allow it to warm up for at least five minutes or you may get a false-negative reading.

Trichograms can also be helpful in diagnosing dermatophytosis. It involves plucking effected hairs and observing in oil under high power looking for the fungal spores occupying the hair shaft.

Just as with Cheyletiella, all cats in the household should be checked because there can be asymptomatic carriers.

The last major differential to consider is pemphigus foliaceus that in some patients is pruritic. Pemphigus foliaceus affects the ear pinna, nipples and nailbeds. Patients will have multifocal crusting on the ear pinna that is often pruritic and/or crusting surrounding the nipples and/or discharge from the nailbeds that does not respond to anti-biotic therapy. A fever may be present as well as a neutrophilia and sometimes mild anemia on complete blood count. The diagnosis is made through skin biopsies.

Malassezia dermatitis is not as common in cats as in dogs. This yeast organism can be diffuse or localized to the facial folds as found in some Persian cats with idiopathic facial dermatitis.

The diagnosis is made by performing cytology on skin smears, staining with Diff-Quik and observing the budding yeast using the oil-immersion lens. Treatment includes systemic antifungals such as ketoconazole or itraconazole, monitoring liver enzymes routinely while the patient is on either.

Once these differentials have been ruled out, the diagnosis of atopy has been made. Most often the cat is steroid responsive, however becomes tolerant after repeated use.

I am often asked what to do for a pruritic cat where steroid injections are no longer working—my response is to first eliminate these differentials, then work the cat up for atopy.

Once the diagnosis of atopy has been made, then several options are available. If the cat is responsive to antihistamines such as chlorpheniramine 4 mg one-half tablet twice daily or amitriptyline 0.5-l mg/kg daily, then control can be achieved by using either of these medications. Most antihistamines are inherently, bitter and cats will salivate when pilled, so the owner must be informed because this is upsetting to some owners.

If antihistamines are not helpful, skin or blood testing for allergy is usually our next step. Not all allergic cats will skin-test positive or blood-test positive for allergy. We usually skin test as our first diagnostic procedure, yet if the test is negative, and I feel (based on eliminating the previously discussed differentials) that the cat is atopic, we will then submit blood for ELISA testing.

The most important aspect of either blood or skin testing is that the test results must match the time of the year the patient is affected. If the cat is a non-seasonal atopic, then dust mite would be the primary suspected allergen. If the patient is affected in the summer season, then grasses or early weeds (in Ohio) would be most likely. Where some veterinarians fail with serum testing is that they do not stop to consider the "whole picture" and match the time of the year the patient is affected with the test results.

Another fault of serum testing is falsepositive readings to molds. Molds tend to be "stickier" and the serum tends to want to bind with them easier than with the other allergens. This should be taken into consideration when opting for what allergens should be included in the immunotherapy. Molds should not be mixed with some seasonal pollens as molds produce protease enzymes that degrade seasonal pollens included in the solution. Cats tend to have a 75 percent excellent response to immunotherapy and some owners feel administering an injection to cats is easier than a pill!

Another option is oral cyclosporine (not FDA approved for cats). Cyclosporine can be used at 5mg/kg/day orally available either as a capsule or oral liquid. Unfortunately, the oral liquid is available in 50-ml bottles that need to be used within 60 days of opening the bottle. Consequently, most pharmacies will not sell a partial bottle and an owner would not use a 50-ml bottle in 60 days.

Considerations when using cyclosporine include side effects of vomiting/diarrhea and making sure there is no underlying neoplasia or infectious disease such as toxoplasmosis that could be enhanced by this immunosuppressive drug. Cyclosporine can be very helpful in atopic cats initially used at a daily dose then every two to three days.

Diagnosing atopy in the cat is not only time consuming but requires a patient owner since many differentials need to be eliminated in order to initially diagnose the disease. Once the diagnosis is made, antihistamines, immunotherapy or oral cyclosporine or a combination of these can be successful in eliminating the chronic use of steroids.

Dr. Jeromin is a pharmacist and veterinary dermatologist in private practice in Cleveland, Ohio. She is a 1989 graduate of The Ohio State University College of Veterinary Medicine and an adjunct professor at Case Western Reserve University's College of Medicine in Cleveland.