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 lesionsEGC 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).
Photo 2: Severe eosinophilic plaque lesions on the ventral abdomen of a cat with flea allergy dermatitis.
Diagnostic techniquesThe 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.
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.
New diseaseInhalant 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.
Photo 6: Facial erythema/alopecia in an atopic cat.
Treatment optionsAlthough 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.