Diagnosis and treatment of atopy in cats

Now that cats have overtaken dogs as the most popular pet in American homes, it seems we're seeing more with dermatological problems. In our practice, feline atopy seems to have had an increased incidence.

Our files show the majority of atopic cats are orange in color or have orange in them (i.e., calico or tortoise-shell colored cats). We certainly see all colors of atopic cats, but overwhelmingly most have orange in their color.

Purebred cats such as Devon Rex also may be predisposed. Allergy in the cat doesn't present with classic signs as it can in the dog, so one must rule out several differentials before arriving at a diagnosis.

Atopic cats can present with symptoms at any age, but the majority seen in our practice seem to be less than 1 year old. They may be steroid-responsive and/or antihistamine or cyclosporine responsive — but so can other atopy-mimicking diseases such as ectoparasites, which is the No. 1 rule-out for atopy in the cat.

Other differentials include food allergy, dermatophytosis, demodicosis, Malassezia dermatitis, pemphigus foliaceus and bacterial pyoderma (not very common in the cat).

Before proceeding with any atopy work-up, take a good history (e.g., age of onset of skin problem, lives indoor/goes outdoors, multiple pets in home. Are there others with a skin problem? Is the pet steroid-responsive? Are symptoms seasonal or nonseasonal?).

It has always been said that diagnosing dermatology cases requires a good history, and that is certainly true with atopy in cats.

Clinical signs of atopy can vary widely in the cat to include: pruritus-facial/rectal/truncal, facial excoriation, eosinophilic granuloma complex lesions, otitis-waxy with or without infection and chin acne. Facial pruritus can range from hair loss of the ear pinnae to severe facial excoriation involving eyes, preauricular areas, commissures of the mouth or chin.

Otitis can be a constant, low-grade waxy otitis without infection to a recurrent yeast otitis. Bacterial otitis may occur but doesn't seem as common as in cats that form wax and yeast.Another sign of atopy I have noticed is alopecia of the hocks.

Ruling out parasites

Before proceeding with any work-up for atopy, it is essential to rule out ectoparasites. Flea-allergy dermatitis and Cheyletiella mites can produce the same clinical signs as atopy in the cat. If you're not getting a history of flea or Cheyletiella exposure, it is still a good idea to empirically treat for ectoparasites and be sure to test and treat all the pets in the household.

With Cheyletiella mites, there can be asymptomatic carriers. Cheyletiella mites can be diagnosed via combings, tape technique or seeing larva/eggs in fecal samples that resemble hookworm eggs, except larger.

We use selamectin topically every 15 days for three doses on all the dogs and cats in the household as well as treat the environment. At the same time, especially in nonseasonally affected cats, it's a good idea to start a hypoallergenic diet trial and continue with that for a good four to six weeks.

I prefer a canned hypoallergenic diet without cereals, grains or cheese because that way food-storage mite allergy can be ruled out. A majority of atopic cats are house dust-mite allergic and are nonseasonally affected, which is why food allergy needs to be ruled out.

Remember that the only valid method of diagnosing food allergy is a hypoallergenic diet trial for four to six weeks. Hypoallergenic means a diet without any ingredients that the cat has been exposed to previously (e.g., corn, wheat, egg, beef, chicken, soy, dairy, fish or lamb).

The biggest problem with special diets in cats is getting them to eat a new food. We dispense a few cans (or zip-lock bags of dry foods) of each flavor to see which the cat prefers. Unfortunately, home cooking is risky because of taurine deficiency. I actually saw that in one cat on a commercially available, hypoallergenic canned diet.

Demodicosis in cats appears to be due to two types of demodex mites: Demodex cati and Demodex gatoi. The latter may be contagious to other cats, and the former may suggest underlying internal-medicine problems such as FIV, FeLV, etc.

Some cats acquire Demodex gatoi due to overuse of systemic steroids, probably administered because of underlying allergy. Both types of demodex mites can be treated with lime sulfur dips topically every five to seven days.

Ivermectin for demodicosis in the cat is risky because of potential neurological side effects, so I prefer to avoid it. Once D. gatoi is cleared with treatment, if the cat is still pruritic, one must try to determine the reason. Occasionally D. cati will present with otitis only, and I have used a few drops of lime sulfur dip two to three times a week in the ears, being careful to have the owners report any increase in inflammation. Be sure when performing ear smears in the cat to also place the ear discharge in a drop of oil and visualize under low power so you won't miss demodectic otitis.

Other less common differentials for feline atopy include pemphigus foliaceus, which usually involves nose, ear pinnae, nail beds and/or nipples. The blistering lesions (pemphigus is Latin for blister) usually present as crusting, often associated with fever. The diagnosis is via skin biopsies. Primary Malassezia yeast dermatitis in cats is uncommon but is seen frequently in Devon Rex cats and may, as in dogs, accompany atopy. The diagnosis is via skin cytologym, and treatment involves antifungals such as ketoconazole or itraconazole.

Idiopathic facial-fold dermatitis of the Persian cat can involve Malassezia as well, but lesions normally are confined to the face.

Testing and treatments

So you suspect you may have an atopic cat and you have treated empirically for ectoparasites, done your four-to-six-week hypoallergenic diet trial and historically the cat has been responsive to steroids. One other positive feature is that the cat is a male, neutered orange tabby with alopecic hocks.

The next step is treatment, which can involve steroids (if used short-term), antihistamines, immunotherapy or cyclosporine. Certainly if immunotherapy is elected, allergy testing via skin or serum is performed to identify which antigens need to be placed in the immunotherapy solution.

In my experience cats do very well on immunotherapy, and many times it's easier to administer a subcutaneous injection than it is to "pill" a cat.

The main drawback is response to therapy time, because immunotherapy can take many months to become effective. Antihistamines, steroids or cyclo-sporine can be used until the desired effect of immunotherapy kicks in.

If you're performing serum testing on cats using Heska's serum test, be sure the positive results correspond with the time of the year the cat is symptomatic. Also steroids and antihistamines can interfere with serum testing, so avoid those for as long as possible before testing. There is no specific down time for steroids because each individual differs with its steroid sensitivity. Some can be tested a month after discontinuation of steroids while others require several months off steroids to get an accurate test.

Cats administered megestrol acetate seem to take longer to be off this medication before positive testing occurs. Our Midwest office deals with specific pollen seasons. Fall is our best season for testing because the animal has just been exposed to spring, summer and fall pollens and year-round house dust mites. The latter can flare when the furnace is turned on and the days grow shorter (dust mites prefer darkness).

Once immunotherapy is started, be sure to tell the owner that if the cat ever seems more pruritic after an injection, they should stop injections and call you. That usually means the dose was too high, and you have caused the cat to become itchy. Some cats are pruritic after the first dose and require a further reduction in dilution right from the start.

If antihistamines, steroids or cyclo-sporine are chosen as the method of treatment, it isn't essential to know what exactly the allergens are that the cat is allergic to. Sometimes we will start with chlorpheniramine 4mg, ½-l tablet bid or clemastine l.34mg, ½ tablet s-bid.

A small percentage of cats will respond to antihistamines only, which is great since you're avoiding steroids. The main drawback with antihistamines is their bitter flavor; excessive salivation may occur, which frightens some owners. Antihistamine tolerance can occur over time. A way to avoid it is to administer the antihistamine daily for three weeks to a month, off one week, then resume. Antihistamines should be used with caution in KCS, pregnant animals, glaucoma, heart disease, megacolon and seizure disorders.

Steroid alternatives

Most owners are referred to a veterinary dermatologist when steroids are no longer effective or underlying disease precludes their use (e.g., diabetes, heart disease).

Because house dust-mite allergy appears to be a common allergen in cats that exists year round, steroids are not an option.

In cases of seasonally affected cats, occasional steroid injections or oral prednisolone may be helpful but long-term use, as always, should be avoided, especially since there are other options.

Although not FDA-approved for use in cats, cyclosporine has become a nice alternative for steroids in treating atopic cats. The drug has been used since the 1970s for feline renal transplants at even higher doses than what is used in dogs (7.5-10mg/kg/day).

For atopic cats, we use 5mg/kg/day in cats or lower to start. I start at a low dose to avoid gastrointestinal side effects of vomiting or diarrhea. We use either the cyclosporine capsules or cyclo-sporine modified oral liquid 100mg/ml, and start at 0.1 mls or bid.

The drawback to the oral liquid is that the 50-ml bottle needs to be used within 60 days. The advantage to the liquid, in my opinion, is less gastrointestinal upset. Be sure to check toxoplasmosis status before starting the liquid because cyclosporine use can cause recrudescence of the disease.

It might be wise to avoid cyclosporine for outdoor cats, considering their potential of eating raw meat. I have seen some develop a mild neutropenia, so it is important to check complete blood counts and serum profiles before and routinely during use.

Once doing well on daily cyclosporine, it is possible to go to alternate-day dosing and even less than that. The advantage of cyclosporine is that it's not a steroid, can be administered orally and doesn't take several months to become effective as is the case with immunotherapy.

Atopy in cats is a reality and can be difficult to treat, let alone diagnose.

Thankfully, there are more options than just steroid injections, which fomerly were considered safe in cats.

Now we know that diabetes, demo-dicosis and heart disease can be associated with steroid use in the cat. Because atopy is for the life of the cat, steroid alternatives, which are much safer, are preferable and available.

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.