Diagnosis and treatment of atopy in cats

Diagnosis and treatment of atopy in cats

Start with a good history
Feb 01, 2009

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.