Cat Rodent Ulcer: Diagnosis and Treatment

The cat rodent ulcer has been called by several names: eosinophilic granuloma, feline eosinophilic granuloma, feline rodent ulcer, indolent ulcer, eosinophilic granuloma ulcer of cats …many fancy names for a very unslightly, unpleasant ulcer found on the lips of cats. It usually occurs on the upper lip, although that is not always the case.

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Just this week, I saw a patient with a feline indolent ulcer. I have included a short video here of the appearance of the lip so you know what to look for if your cat ever has one. The cat in the video gets these indolent ulcers in the spring and fall each year and one injection of steroid usually clears it up. That gives reason to believe it is allergic in nature because it is seasonal.






What Causes Cat Rodent Ulcers?


The term rodent ulcer comes from an old belief that these mouth sores in cats were caused by a rodent bite or infection caught from a rodent. We know now that this is not true. The exact cause is frequently not known. There are believed to be links to allergies, abnormalities in the cat’s immune system, dental disease, contact with plastic or rubber food or water dishes – in many cases, you may never know the cause.

In fact, the underlying cause of indolent ulcers in cats is most often never revealed. Again, the possibilities include

(1) allergies, such as an allergy to food, fleas, or pollens and other things in the environment.

(2) There has been some research that seems to indicate that at least some cases may be genetic in origin.

(3) There have been other studies that implicate an autoimmune reaction as the possible cause. Autoimmune diseases occur when the body sees some part of itself as foreign.


Not that you shouldn’t try to find the cause. You should work with your veterinarian to search for the underlying cause of cat rodent ulcers because they can be difficult to get rid of otherwise and can continue to plague your cat for a lifetime.

It is generally recommended that any cat with an indolent ulcer should be tested for Feline Leukemia. I certainly am not going to disagree with that, but I will tell you that in my twenty years of treating rodent ulcers in cats, not a single one of them has been positive for Feline Leukemia.


I’m much more interested in exploring the possible allergies the cat may have. Evaluation for allergies can include skin allergy tests, food sensitivity trials, evaluation of the result to steroid treatment, flea elimination, although certainly infectious agents such as viruses, fungal, and bacterial have to be considered as well as trauma.


While they may not seem to bother your cat at first, if they become large enough (and they most often do), they will be painful and cause a decline in eating.



How Do These Cat Lip Ulcers Form?


Without getting too complicated, I’ll try to explain how these feline rodent ulcers form.

Feline indolent ulcers are considered to be part of a larger disease group called feline eosinophilic granuloma complex. This term refers to a group of skin diseases of cats that includes not only the rodent ulcers but also lesions called eosinophilic plaques (usually found on the abdomen and thighs) and eosinophilic granulomas (linear lesions on the caudal thighs, face, tongue and palate, and including swollen lower lips and chin). These are inflammatory lesions that often affect the same cat and all respond to the same type of therapy and may have the same underlying cause.

An eosinophil is a type of white blood cell. Regardless of which underlying cause is correct, inflammation occurs in response to parasites or microorganisms or antigen-antibody complexes. When there are irritated tissues or allergic reactions in the body with inflammation produced, eosinophils respond to this inflammation, move in and the eosinophilic granulomas are created.


Diagnosis of Feline Eosinophilic Granuloma Complex Ulcers


Diagnosis is generally made just by your veterinarian examining the lesion. Only in rare cases is a biopsy indicated. If the ulcer does not respond to treatment or is constantly recurring and becomes extremely large and unusual in appearance, your vet may want a biopsy to exclude cancer.


Treatment of Cat Indolent Ulcers


Treatment almost always requires steroids. A long-acting injection is usually given, but if it becomes necessary to repeat the injection in just a few week, it is safer and healthier to try having the owner give oral prednisolone.

If your cat is being referred to a veterinary dermatologist for skin testing for feline allergies, you will need to speak to the dermatologist regarding the length of time your kitty needs to be completely off steroids before the testing. Steroids in the cat’s system interfere with accurate allergy test results.

If there is any suspicion of fleas or other parasites, then your veterinarian will also suggest flea treatment. If your cat has been drinking or eating from plastic or rubber bowls, it is always worth a try to eliminate those types of dishes. Also, if your vet is at all suspicious of food allergy, he will discuss a food allergy trial with you. Again, it is important to attempt to get to the underlying cause of feline eosinophilic granuloma complex if at all possible.




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