Rodent Ulcers aka Indolent Ulcers in Cats

Learn the causes and treatments for rodent ulcers aka indolent ulcers in cats.

Let’s kick this off answering your #1 question: Rodent ulcers ARE NOT caused by rodents. Phew! Next, the fact that they’re called rodent ulcers is technically incorrect and the correct term is indolent ulcers (which I learned writing this post). Rodent ulcer is apparently sooooo 1900s and it is actually a term used to describe a type of cancer in humans. There’s more. Indolent ulcers are under the umbrella of feline eosinophilic granuloma complex. Huh? I know. It’s basically how science describes a family of skin lesions found on cats. Now that we have that out of the way, let’s take a deeper look indolent ulcers.

What Are Indolent Ulcers?

Close-up of indolent ulcer
Most indolent ulcers are on the top lip but this is on the bottom.

An indolent ulcer may start as the gum thickening, and then excessive licking causes more inflammation. Typically, it looks like a cat has swollen gums on the top or bottom lip, either on half the lip or across the entire lip. If a cat has it on the bottom, it sort of looks like they’re constantly sticking out their tongue. My first thought when I saw a cat with one was that it looked so painful. Good news: Science says they’re usually painless. The word “indolent” comes from the Latin term “indolens” for “without pain.”

What Causes an Indolent Ulcer?

black and white cat lying down
Indolent ulcers are almost always painless, which is why Alfredo looks so content here.

Usually, indolent ulcers are the result of overactive eosinophils, which are white blood cells that apparently come to the scene and decide it’s a party. (This is similar to eosinophilic keratitis, which I wrote about previously.) The eosinophils damage the collagen resulting in the ulcer.

The most likely underlying cause of an indolent ulcer is hypersensitivity which is a bougie term for allergies. The most common is a flea allergy (cat’s allergic to flea saliva). A food allergy, nonfood allergy, and insect bite hypersenitivity may also be the underlying cause but are less common.

Additionally, you cannot overlook the fact that cats in shelters get these, which is further support for other possible causes, like viruses (feline herpes aka kitty cold the most common), bacterial infections, fungi, and cancer.

Treatments for Indolent Ulcers

Honestly, there are a lot of treatment possibilities. It really depends on the driving force behind the ulcer. Like I mentioned, allergies are the most common reason, but allergies take a long time to diagnose (just read my article My Neck, My Back, Allergies in My Cat).

The best course of action:

  • Flea prevention
  • Steroids to take down the inflammation
  • An antibiotic, because even if the main cause is an allergy a secondary bacterial infection is possible. Also, antibiotics have been shown to be more effective than previously thought.
Black and white cat with long whiskers
Fredo’s indolent ulcer is improving with a combo of a steroid + antibiotics.

For indolent ulcers that don’t respond to flea prevention, steroids, and antibiotics, long-term management is necessary. The next step would likely be to rule out food allergies with a food trial, which takes 6-8 weeks. Your vet could recommend select protein or hydrolyzed protein diets. The goal is to start with the most likely culprit in food allergies: the protein. Trying nontraditional proteins like rabbit, bison, kangaroo, and even alligator are options.

If a cat fails a food trial, it’s likely another type of allergy. With nonfood allergies, there are other physical symptoms you’d notice: excessive scratching or grooming around the neck and head (especially around the ears) and miliary dermatitis. Treatments for nonfood allergies include antihistamines and cyclosporine (brand name: Atopica).

Side note: Cyclosporine also has anti-inflammatory properties, making it a nice option to treat allergies and indolent ulcers.

Case Study: Alfredo

Black and white cat
Alfredo is easily able to close his mouth now, but if you open it you can see the ulcer is still there.

One of my current fosters is from Stray Cat Relief Fund, and came to me with what looked like a pretty big indolent ulcer. He was treated with a course of antibiotics and steroids. After a week and a half, he is healing but isn’t quite there yet. We are keeping him on the steroid for two more weeks, hoping it will kick it out!

I hope you enjoyed this article. Feel free to take a look at a few of my sources:

By LizsKittyBootCamp

Hi, I'm Liz, and I'm a cat behaviorist who provides advice and insights on cat behavior.

2 replies on “Rodent Ulcers aka Indolent Ulcers in Cats”

Hi there! I’ve been doing as much research on this as I can for my own little girl…. how much info is there on how the ulcer heals? If a cat looks like they are missing skin or receding lip line, is there any chance of the cat NOT being permanently disfigured? Thank you for your time!

Hi Alexis. The cats I’ve seen with them have all been okay once it was healed but I would check with your vet as they’ve seen a lot more than I have.

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