'Why is my cat scratching its face?'

We have pretty much resolved ourselves to pigeonholing our pruritic dogs into the categories of atopy, food allergy and ectoparasites as a reason for their itching.

Alice Jeromin, DVM, Dipl. ACVD

Flea allergy usually appears as "naked butt," atopy most often is face and feet involvement, and food allergy can be itchy at any time of the year, age or place on the body.

However when it comes to the feline species, they don't like to be "typical" in any way! The most frustrating dermatology problems in cats are those cases that "pull their hair out" yet respond to steroid injections with the ultimate problem of becoming steroid tolerant. And the problem still isn't solved.

Photo 1: Although flea allergy dermatitis can have many different clinical appearances, this patient has dorsal lumbar alopecia.

These patients need consideration through a series of differentials that can hopefully prevent the overuse of steroids and truly eliminate or control the problem. Differentials for the pruritic cat will be discussed with special attention to those that are pruritic around the face and head.

Ectoparasite infestations, including allergy to ectoparasites, is the most common allergy in cats. In fact, flea allergy historically has been at the top of the list of feline allergies. It would be nice to think that with the improved flea treatments we have seen over the past 10 years that flea allergy would be less of a problem. Perhaps what is more of a problem is convincing the owner that flea allergy dermatitis (FAD) is the entire problem as many owners feel that "one or two fleas is normal." In a multiple cat household, particularly where the cats go outside, flea allergy or other ectoparasites such as Notoedres (feline scabies) or Cheyletiella should be the top consideration.

Very common allergy

All the cats in the household (including other pets such as dogs, rabbits and ferrets), need to be combed or scraped to rule out ectoparasites. Particular attention should be paid to elderly pets with internal medicine problems or those that are kenneled or groomed. We have found Cheyletiella most often on those animals, yet they can be asymptomatic.

Photo 2: Periocular excoriation affects this cat with Cheyletiella.

If you strongly feel ectoparasites are a possibility - for example an elderly cat that was never pruritic that has now become pruritic and visits a groomer - don't be disappointed if you do not find the flea or mite because the patient may have just been bathed. We try to check our patients for ectoparasites without bathing for at least two weeks.

In Ohio, we actually see more problems with Cheyletiella mites than fleas possibly because the flea products are very good at eradicating fleas. Formerly, pyrethrin-based products such as powders, shampoos and dips were used on cats for flea control and those also killed Cheyletiella mites.

However most of the newer flea products, although much safer and easier to use, will not treat Notoedres or Cheyletiella. My choice for flea control on cats is to use Advantage, Revolution or Frontline Topspot on all the cats in the household every 15 days for the first two doses, then once monthly. Also treat the house with an environmental spray containing a pyrethrin derivative and insect growth regulator.

Photo 3: The Cheyletiella mite is readily visible under low power microscopic examination.

In Ohio, our main flea season is August-December, so we concentrate on that time period, but in a very flea allergic patient, I recommend monthly topical treatment.

Unlike dogs with FAD, cats tend to have a variety of clinical presentations ranging from "rattail" to facial mutilation to miliary dermatitis to eosinophilic granuloma complex (EGC) lesions.

Clinical presentations

Cats with Cheyletiella mites may not have the typical clinical appearance of dorsal lumbar dandruff. In spite of its lay terminology of "walking dandruff," some cats present with EGC, miliary dermatitis or facial pruritus including chin acne, otitis and sneezing. Reportedly, the Cheyletiella mite can and likes to crawl into and out of nostrils and ears resulting in facial pruritus. The mites can be diagnosed by combings, tapings or scrapings as viewed under low power under the microscope.

Photo 4: The cat suffers from generalized Demodex gatoi.

When mites are not found, skin biopsies reading out as superficial perivascular dermatitis with eosinophils or EGC are suspicious for ectoparasites. For Cheyletiella mites, we use Revolution topically every 15 days for three doses and again use environmental treatment as the mites can reportedly live in the environment for up to 21 days. Bedding needs to be laundered and floors damp mopped as well as cloth toys and grooming utensils treated. Other treatments effective for Cheyletiella include ivermectin (not approved for use in the cat and must be heartworm negative first) 200ug/kg/wk x three weeks, or Frontline Spray one spritz/lb body weight repeated again in three weeks, or lime sulfur dips every five to seven days for one month.

Notoedres is more of a regional disease, i.e. there are "pockets" of feline scabies in different areas across the country. The clinical appearance is usually that of extreme crusting of the face and ears. The mite is relatively easy to find in skin scrapings unlike the scabies mite in dogs that can be difficult. Treatment consists of ivermectin (not approved for use in cats, should test negative for heartworm first) 200ug/kg/wk x three doses, Revolution 15 days x three doses, or lime sulfur dips every five to seven days for one month.

Otodectes (ear mites) can also cause a diffuse pruritus as well as facial/head itching. Aside from visualizing the mites via an otoscope or placing ear smears in oil, occasionally Otodectes mites are diagnosed via combings particularly of the tail area. Treatment, as for the other mentioned ectoparasites, includes treatment of all the cats with topical Revolution, one tube every 15-30 days x two doses, ivermectin 200ug/kg/wk x two to three weeks, or topical preparations such as Tresaderm, or Milbemite. In persistent Otodectes infestations, the patient needs to be checked for FIV or FeLV.

Ear mites

Photo 5: Demodex gatoi mite

Less common but still considered ectoparasites include the two feline demodex species-Demodex gatoi and Demodex cati. The relatively newly described Demodex gatoi (formerly unnamed demodex species) is a short, stubby mite that can easily be found in combings or scrapings of the dorsal or ventral trunk or head.

Most felines are pruritic and some have a mild flaking. Demodex gatoi can be associated with underlying allergy such as food allergy or be the result of overuse of steroids. Treatment includes lime sulfur dips every five to seven days until one to two dips past a negative combing/scraping. All the cats in the household should be treated as the mite has been found to be contagious.

If pruritus remains after treatment, yet no mites are detected, search for another underlying allergy such as atopy or food allergy.

Demodex cati is the more serious of the two Demodex mite infestations. In generalized demodicosis, an internal medicine disease such as diabetes, FIV or FeLV needs to be considered. The mite has a long thin body and resembles Demodex canis. Mites can be found in ear smears in oil or easily in skin scrapings. The clinical appearance is one of alopecia, scaling or a papular/crusting dermatitis with pruritus. In some patients with only pruritus and lesions of the head, Demodex cati is confined to the ears and detected on ear smears in oil.

Demodex infestations

Photo 6: Preauricular excoriation in a patient with Demodex cati otitis.

Treatment for ear infestations consists of lime sulfur drops instilled into the ears or topical ear mite treatments including Milbemite or Tresaderm. Treatment for diffuse demodicosis due to Demodex cati consists of lime sulfur dips every five to seven days. Amitraz has been used in cats at 125ppm but due to its unavailability and nonapproved use in the cat, lime dip has become the drug of choice.

These ectoparasites are the main differentials to be considered in pruritic cats particularly those with facial pruritus. Second would include allergies such as food allergy or inhalant allergy (atopy). Formerly, cats that had mainly facial/head pruritus were considered to be food allergic.

Main differentials

That is still true as in one study 69 percent of food allergic cats had ear involvement and 62 percent had facial involvement. Other manifestations of food allergy in the cat include EGC lesions, miliary dermatitis, chronic ceruminous otitis, gastrointestinal problems and facial fold dermatitis. Food allergic cats may be initially responsive to steroids unlike in the past when it was felt they were not steroid responsive.

Cats may be nonseasonally affected, of varying age and may have eaten the same food for years. Since blood or skin testing for food allergy has not been shown to be reliable, a hypoallergenic diet for four to six weeks needs to be undertaken. Remember to not give any other foods, treats or snacks while on the diet. A hypoallergenic diet consists of ingredients to which the patient has not been exposed, i.e. corn, wheat, egg, beef, chicken, soy, dairy and lamb.

Photo 7: Facial excoriation in a food allergic cat.

Most often this means dispensing a prescription diet such as venison/pea, rabbit/pea, duck/pea or lamb/barley assuming the cat has not eaten lamb previously. The main problem in cats is getting them to eat the new food, therefore it should be introduced slowly and mixed in with the current diet.

Occasionally a patient will be allergic to food storage mites found in any dry foods, cereals, grains or cheese. Those patients need to be weaned off all dry foods and onto canned, or cooked food only, and usually respond to the diet change in two to four weeks. Food storage mite has recently become a focus of investigation of pruritus in both dogs and cats and hopefully we will be learning more about it in the future.

There are several studies to suggest that atopy exists in cats. For those of us in practice, we would agree that atopy is probably more prevalent than food allergy as a cause of pruritus. This is particularly true in the non-seasonally pruritic cat that responds to steroids as house dust mite is the most common allergen in the cat.

Some atopic cats present clinically as does the atopic dog i.e. face and feet involvement. Yet, others present with EGC lesions, miliary dermatitis, chin acne, ceruminous otitis or a diffuse exfoliative dermatitis. Of the facial presentations, the most common signs we see are chin acne type lesions with involvement of the commissures of the lips and a ceruminous otitis, sometimes with yeast involvement.

Photo 8: Chin acne as a presentation of underlying feline atopy.

Steroids clear the lesions, but they recur once the medication wears off. Topicals can help with the quality of the chin skin but do nothing for the pruritus.

Once ectoparasites and food allergy have been ruled out, atopy should be strongly considered and skin or blood testing pursued. A key to being successful in treatment of atopy in any species is to be sure the skin or blood test results match with the time of the year the patient is affected. For example, a winter or non-seasonally affected patient would be suspicious of being allergic to the house dust mite or food storage mite, yet in the Midwest a patient itchy only in the spring would most likely be tree allergic. In the Midwest, trees are first to pollinate in the spring, grasses in summer, weeds in the fall with the house dust mite being all year round. Molds are worse in wet seasons such as spring and fall.

The most common mistake made when blood testing an allergic patient is not interpreting the results and being sure they make sense. Immunotherapy, antihistamine therapy or oral cyclosporine 5mg/kg/day (not approved for use in the cat, must be FIV/FeLV negative with no detectable neoplasia) may then be instituted for the atopic cat. Success rates for immunotherapy in atopic cats approach 65-75 percent, and many owners find it easier to administer injections to their cats than administering oral medications.

Photo 9: Hind leg alopecia in an atopic cat.

Remember the most common differentials for feline facial pruritus are ectoparasites, food allergy and atopy. These three differentials probably account for about 90 percent of facially pruritic cats with ectoparasites overwhelmingly being number one. The remaining differentials of dermatophytes, bacterial pyoderma, viral diseases, Malassezia dermatitis and idiopathic facial fold dermatitis will be addressed in the next part of this article in May.