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Why Do Cats Get Mouth Sores? And How Are They Treated?

Eosinophilic granulomas, or rodent ulcers, are common causes of pain and facial deformation.

 |  Feb 25th 2014  |   5 Contributions


I received the following question from Candice a short time ago by way of my Facebook page.

I checked out your article regarding eosinophilic granulomas (rodent ulcers) in cats. The vet that we've taken our indoor/ outdoor cat Tippy, to has a hard time discussing anything with his owner, Jim. He's only told Jim that there may not be much of anything he can do for the cat without bloodwork and other costly tests, and that he can just give Tippy steroid shots for it, but not more than 3 of them, and that it probably won't resolve the issue entirely. He won't even give us a specific name for what it could possibly be, I'm assuming because he wants to keep our business with him, or not misdiagnose the problem. Any advice or help with this situation would be greatly appreciated. I would feel horrible if the owner put this usually sweet, healthy cat to rest over a matter of financial issues. Thank you, in advance! ~Candice

It sounds like Jim and his veterinarian are having no small amount of difficulty communicating -- to the point that Jim and Candice aren't sure of Tippy's diagnosis. However, Candice describes a beautiful black cat with severe erosions (ulcers) effacing (destroying) her upper lip in a symmetrical fashion. The lower lip is also symmetrically swollen and ulcerated. This is consistent with eosinophilic granulomas, or rodent ulcers.

Photo of Dr. Eric Barchas by Liz Acosta

The term rodent ulcer is a colloquialism. It's a holdover from days in which veterinary medicine had a poor understanding of these common swellings and ulcers that develop on cats' mouths. In the olden days, vets thought the ulcers occurred in cats' mouths after they were bitten by prey animals, which are mostly rodents.

In fact, Tom and Jerry and Itchy and Scratchy not withstanding, when cats and mice (or other rodents) interact, the damage is generally one sided, and it's not the mouse that comes out on top. Cats know what they're doing, and they rarely suffer hunting injuries.

Rodent ulcers, therefore, have nothing to do with rodents. Rather, they occur when cats' immune systems become hyperactive in a special way. Those hyperactive immune systems attack the lips, and cause plaques or ulcers to develop. When evaluated under a microscope, cells called eosinophils are prevalent in the ulcers, which are made of tissue that has responded to inflammation by forming complexes known as granulomas. Hence, the other name for the condition: eosinophilic granuloma complex.

Rats are icky, sure, but they don't often injure cats who are after them. Brown rat by Shutterstock.

Eosinophilic granulomas occur most frequently on the midline of the upper lip, but other areas and the lower lips can be affected. They are usually symmetrical lesions that appear to cause equal damage on both sides of the face. They may be red and inflamed, or white, malodorous, and infected.

Eosinophilic granulomas can be disfiguring. They may cause the lip to erode away permanently. They are also very painful -- cats with the problem may suffer from behavior changes (including aggression) and weight loss. I once knew a frighteningly fractious cat with the syndrome. Once the condition was controlled she became an absolute sweetheart.

There are three broad approaches to dealing with eosinophilic granulomas. The first is to avoid things that cause antigenic stimulation, which is a fancy way of saying avoid things that excite the immune system. The second is to administer medications to attenuate the immune system's activity. The third is to treat for pain.

The number one antigenic stimulator in cats, by a mile, is fleas. Fleas are probably playing a significant role in Tippy's condition even if she doesn't have a visible flea infestation. Jim should be absolutely religious about using flea control regularly. Comfortis has been recently approved for use in cats and it seems to work better than anything else in my experience. Advantage still does a decent job, and I have seen many people safely combine Comfortis and Advantage in cats (although Jim should talk to his vet before combining products).

The great outdoors is full of antigens. Although fleas and mosquitoes can move freely between the indoor and outdoor worlds, they are more readily encountered outside. So are plant pollen and countless other items that might stimulate Tippy's immune system. I'd recommend that she be kept indoors to reduce her exposure to them.

Indoors is safer … and cozier. A cat sits near a window by Shutterstock.

There are a variety of medications used to treat eosinophilic granulomas. Most of them are steroids similar to cortisone. I'm guessing that the shots Tippy has been receiving are called Depo Medrol. Depo Medrol is a potent steroid injection that lasts two to four weeks. Many vets don't like to give it more than three times because they worry about side effects (the medicine can trigger diabetes and also can exacerbate heart failure). However, if Tippy's choices are to keep getting the injections or be put to sleep, I'm sure she'd rather take her chances with some additional shots.

Given that each shot only lasts two to four weeks, and severe eosinophilic granulomas can take many months to resolve, it's very likely that more than three Depo Medrol injections would be necessary to eliminate the problem.

Oral medications, especially one called prednisolone, also can treat eosinophilic granulomas. Oral medications are preferred to injections because they give owners much more control over the steroid dose received. Cats on prednisolone can benefit from tapering doses that ultimately allow the owner to administer the minimum effective amount of medication to control the problem.

Cat with an open mouth by Shutterstock.

Other immune system modulating drugs such as cyclosporine are sometimes used. Hypoallergenic diets are also sometimes recommended.

Remember that eosinophilic granulomas are painful. Cats should receive pain killers such as tramadol or buprenorphine while the lesions are being treated.

Eosinophilic granulomas can be frustrating and difficult to treat, but if the owner is sufficiently dedicated most cases can be brought under control.

I would recommend that Jim talk to his vet about antigen avoidance, oral pain killers, and prednisolone. It seems to me that there are many options besides euthanasia for poor Tippy.

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