When steroids quit workingfor eosinophilic granuloma complex in cats

Q. I have a cat with a rodent ulcer that used to respond to steroid injections. Is there anything new for this?

A. I am faced with this question at least once weekly from referring veterinarians. My response is: I wish it were that simple!

Unfortunately, there is no standard therapy for eosinophilic granuloma complex (EGC) lesions in cats that doesn't involve finding out the etiology of the likely underlying allergy ... and that takes some detective work. Formerly, most of us treated EGC lesions with methylprednisolone acetate injections every two weeks for a total of three injections. Now that we are more cognizant of steroids inciting diabetes in cats or reports of even one dose of methylprednisolone acetate weakening cardiac muscle, a more concerted effort must be made to determine the underlying reason for the EGC lesion(s). Underlying allergy (ectoparasite, food allergy, food storage mite allergy, contact allergy or atopy), bacterial infection, or inheritability seem to be at the underlying etiology of most cases of EGC lesions.

Photo 1: Eosinophilic plaque lesions on ventral abdomen. Note the red, raised, almost "glistening" quality to the lesions.

EGC lesions consist of feline indolent ulcer (rodent ulcer), eosinophilic plaque and eosinophilic granuloma (Photos 1 and 2). A patient may have one or a combination of lesions at the same time. Indolent ulcers involve the upper lip and sometimes the oral cavity. Usually accompanying eosinophilia is not present. Occasionally indolent ulcers can undergo a malignant transformation. Feline eosinophilic plaques are usually seen on the ventral abdomen or medial thighs. The owner reports constant licking of the area and the lesions reflect this attention-erythemic, raised, weeping and usually multiple. Systemic eosinophilia is often present. Cytology of a lesion reveals eosinophils and neutrophils. Linear granuloma is usually seen on the caudal thighs and consists of yellow-to-pink raised non pruritic plaques arranged in a linear fashion. Of the three types of lesions, linear granulomas are most often seen in young cats <l year of age sometimes resolving spontaneously without treatment. This lesion also accounts for lower lip and chin swellings in some patients (Photo 3).

EGC lesions

Photo 2: Severe eosinophilic plaque lesions on the ventral abdomen of a cat with flea allergy dermatitis.

The diagnosis of EGC is not difficult in that it is based on the clinical appearance of the lesion, cytology, skin biopsy, blood eosinophil count, +/- lymphadenopathy (usually in indolent ulcers or eosinophilic granulomas). However what is difficult is determining the underlying etiology of the lesion.

Diagnostic techniques

Photo 3: Upper lip thickening in a cat with "rodent ulcer."

In multi-cat households, ectoparasites should be the first differential to be considered. Flea allergy dermatitis (FAD) should be considered in all cases of EGC lesions particularly in multi-cat households or if the cat is allowed to go outside. All cats in the household should be flea combed and treated with an adulticide/larvicide as well as the environment. Unfortunately, if the patient is allowed to go outdoors, the problem may never be resolved. If fleas are determined to be the problem, we treat all the pets, both dog and cat, with imidacloprid every 14 days for the first two doses, then once monthly. The house is treated with an adulticide and insect growth regulator after a thorough cleaning and vacuuming. Cheyletiella mites ("walking dandruff") should also be ruled out by combings, scrapings or the scotch tape technique. Again, check any and all accompanying pets in the household as asymptomatic carriers may be present. Treatment for Cheyletiella includes ivermectin 200 ug/kg once weekly for three weeks (not approved for use in cats) or selamectin used every 14 days for a total of three doses on all the pets along with treatment of the environment. Selamectin should not be used in patients with underlying internal medicine disease or in patients <8 weeks of age.

Photo 4: Rectal erythema/hyperplasia in a cat with food allergy.

Food allergy has been discussed in past articles on feline allergies but we need to keep it in mind particularly in EGC lesions that are nonseasonal (Photo 4). Since blood or skin testing for food allergy has not been shown to be valid, a four to six week hypoallergenic diet consisting of a novel protein without any ingredients to which the patient has been exposed should be undertaken. There may be difficulty in getting the patient to eat the new diet, so we frequently dispense small amounts of each diet in dry and canned form for the owner to offer the cat. Whichever diet the cat prefers is then relayed to our office or the referring veterinarian so that it can be ordered in.

Photo 5: Facial excoriation in a patient with food storage mite allergy.

The food storage mite (T. putrescentiae) is a mite found in dry pet foods, grains, cereals and cheese and may be responsible for underlying allergy in the cat and dog (Photo 5). The diagnosis is made by skin or blood testing for the mite or feeding a canned or cooked diet without any dry ingredients for four weeks. Food storage mite may cross react with house dust mite on some ELISA tests. When results indicate both food storage mite and house dust mite allergy, we routinely have the owner feed the cat a canned or cooked diet for the next month before attempting immunotherapy for the house dust mite allergy. In my experience, I have not had much success in attempting to hyposensitize for food storage mite - the diet change seems to be more effective. This mite has recently come into focus in veterinary dermatology and there appears to be much to learn about its manifestations, concentration for skin testing and treatment. It may be playing a role in those patients formerly found to be house dust mite allergic only (we were not testing for T. putrescientae up until one to two years ago) and not doing well on their immunotherapy.

Inhalant allergy or atopy is a relatively newly discovered disease in the cat and should be a consideration in patients with EGC (Photo 6). House dust mite allergy should be considered in cats with nonseasonal lesions. In those patients that flare with lesions at predictable times of the year, allergy to seasonal pollens should be considered. In indoor cats, house dust mite has been found to be a popular allergen. Steroid therapy may be considered in those patients affected <three months/year but in those patients with symptoms lasting longer, safer alternatives need to be considered. Again first and foremost, ectoparasites must be ruled out and/or treated. Antihistamines such as chlorpheniramine 4 mg. (11/42 tablet bid), clemastine 1.68 mg (11/42 tablet bid), or amitriptyline 10 mg (-l tablet sid) along with fatty acids may be used. Antihistamines are notoriously bitter and cats may salivate after their administration often upsetting the owner if not forewarned. Immunotherapy based on blood or skin testing for allergy where the results correlate with the time of the year the cat is affected may be successful in 60-70 percent of patients. Oral cyclosporine 5 mg/kg/day has been helpful in some atopic cats. Long-term use of cyclosporine for atopy in cats has not been studied.

New disease

Photo 6: Facial erythema/alopecia in an atopic cat.

Although most EGC lesions show no growth on culture and sensitivity, occasionally some of these lesions will respond to antibiotic therapy. Doxycycline 5 mg/kg bid has been successful possibly due to its antibacterial effect as well as other effects it seems to have on mast cells and eosinophils. It needs to be administered with food as it can cause esophageal strictures if it remains in the esophagus for prolonged periods of time. Other antibiotics include Clavamox 10 mg/lb bid, cephalexin 10 mg/lb bid or Antirobe 5 mg/lb/day.

Treatment options

So, unfortunately, the next time a feline patient presents with EGC lesions it means a lot of detective work! A thorough history of how long the patient has had the lesion, if the cat is strictly indoors, goes to a groomer or kennel, if the lesion is seasonal or nonseasonal, and whether it responds to steroid therapy and for how long needs to be determined before any of the undercover work begins. The first step should be ruling out ectoparasites by checking this patient and any other accompanying pets in the household for fleas or mites and treating those patients and the environment. Antibiotics mentioned above should be administered thereby ruling out the small percentage of EGC lesions that are bacterial in origin. The next steps involve ruling out food allergy, food storage mites and atopy. Which should be done first is determined by whether or not the patient is affected seasonally or nonseasonally. Food allergic patients are usually nonseasonal, but keep in mind so are house dust mite allergic patients. Don't forget food storage mites can easily be ruled out by feeding a nondry diet. Food allergy and food storage mite allergy can simultaneously be tested for by feeding a hypoallergenic canned diet for four to six weeks.

Photo 7: The equivalent of an acral lick dermatitis lesion in a cat with inhalant allergy.