Rodent Ulcers in Cats

A rodent ulcer begins as a yellow or pink shiny spot that deepens and becomes an open sore. Often, it begins on either side of center on the upper lip. Less commonly, it occurs on the lower lip or at the back of the jaw behind one of the last upper molars. Some cats will also develop an ulcer on the tongue. It is not itchy and seems to cause no pain. As the ulcer advances, the lip may be partly eroded by a large, ulcerated swelling that exposes teeth and gums.

This unsightly condition is unique to the cat. It may be found in cats of any age, and occurs three times more often in females than males. The exact cause of rodent ulcer is unknown, and there is actually no direct connection with rodents. The presence of eosinophils suggests an allergic reaction, parasite problem, or immune problem. It is thought to be part of the eosinophilic granuloma complex. Hypersensitivity is strongly suggested, with causative agents including insects, environmental substances, and diet. Flea allergy should always be considered as a possible cause. Some cases are associated with dental infection. An underlying genetic predisposition is suspected.

Rodent ulcers have been found in cats who were exposed to the feline leukemia virus, further suggesting that impaired immunity may be a cause. However, not all cats with rodent ulcer test positive for the feline leukemia virus, nor does a rodent ulcer necessarily mean that a cat has feline leukemia.

Diagnosis is suggested by the typical appearance and location of the ulcer. In questionable cases, a biopsy or needle aspirate cytology can be done to rule out malignant transformation. Cats with rodent ulcer should be tested for Feline Leukemia.

Treatment: Veterinary care is required in all cases. Cortisone has proven to be the most effective treatment, but it should be given with an antibiotic, at least initially, to clear up any secondary bacterial infection. Cortisone is given either as pills (prednisone) or by injection (Depo-medrol). Depo-medrol is a long-lasting injection that is given at two-week intervals. Usually, three courses are necessary. Alternately, prednisone can be given daily until the ulcer disappears. If the ulcer recurs after either injectable or oral cortisone therapy, the cat is placed on prednisone maintenance-usually one pill every other day. Essential fatty acid supplements may also be beneficial.

In case this is the result of an allergen or irritant, do not use plastic or rubber food and water bowls. Stainless steel is a good alternative.

Cyclosporine, interferon, radiation therapy, and cryosurgery may all be effective. Gold salts, given as an injection, may also be used for treatment in cases that are difficult to treat.

Megestrol acetate (Megace) has been used in some cases of rodent ulcer. However, this progesterone drug is not approved for cats and has serious undesirable side effects. It is best used as a last line of treatment under veterinary supervision. These ulcers are known to recur, so it is worthwhile to try to find and eliminate the underlying cause.

This article is excerpted from “Cat Owner’s Home Veterinary Handbook” with permission from Wiley Publishing, Inc.

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