As you lean in to boop heads with your feline friend, they turn up their nose at the last minute, and you notice an angry-looking sore around their lips. What could have caused such a wound? Did your cat chew on an electrical cord, or tangle with some other hazardous object? This painful-looking sore is actually an eosinophilic ulcer, also known as a feline indolent ulcer, or a rodent ulcer. Let’s take a closer look at this condition that can startle cat owners.

What are eosinophilic ulcers in cats?

Eosinophilic ulcers are part of a disease group termed eosinophilic granuloma complex (EGC). These inflammatory skin problems can be caused by a number of underlying conditions, but most likely are the result of an allergic disorder. Eosinophilic granulomas can occur anywhere, but most appear in the mouth, hind legs, and paw pads. Eosinophilic plaques can also occur anywhere on the body, but are most commonly seen on the ventral abdomen. These ulcers are found on the edge of the upper lip in cats, and can develop on one or both sides, but typically are near the front. 

What causes eosinophilic ulcers in cats?

Since eosinophilic ulcers are part of the EGC, they are generally caused by some sort of allergic disease. Flea bite hypersensitivity is the most common culprit. Feline atopy, insect bite hypersensitivity, food allergies, inflammation, or trauma can also cause the lesions. 

What do eosinophilic ulcers look like in cats?

Eosinophilic ulcers in cats create on the upper lip a clearly demarcated lesion that may have a raised border. The ulcer can also cause marked lip swelling in the ulcerated area. These lesions can become large and extensive in severe cases, and shock the pet owner. Additionally, some ulcers may develop a discharge. 

How are eosinophilic ulcers in cats diagnosed?

Eosinophilic ulcers typically aren’t painful in cats, so they can be tough to spot, unless you actively check out your cat’s lips. They’re often noticed incidentally, or during a routine veterinary exam for a wellness visit or dermatological issue. In many cases, a preliminary diagnosis is based on the ulcer’s general appearance, especially if allergy issues are present.

However, to help reach a definitive diagnosis, an impression cytology must be performed. In this test, a slide is pressed against the ulcer to pick up cells, bacteria, and other organic matter to help determine what is causing the lesion. If bacteria are present, a sample may be taken for a culture and sensitivity test, to find the appropriate antibiotic for treatment. In some cases, a biopsy and histopathology are needed to confirm an eosinophilic ulcer diagnosis.

One major differential eosinophilic ulcer diagnosis in cats is squamous cell carcinoma. Additional differential diagnoses include fungal infection, feline herpes virus type 1 infection, trauma, lymphoma, and mast cell tumors. Histopathology helps to differentiate eosinophilic ulcers from other diseases.

How are eosinophilic ulcers in cats treated?

Since eosinophilic ulcers are typically the result of allergic disease, the underlying cause must be treated to clear up the lesion. Possible treatments include:

  • Flea bite hypersensitivity treatment — Flea bite hypersensitivity most commonly causes eosinophilic ulcers, and keeping every pet in the household on year-round flea prevention is an easy fix. However, treating the environment and eradicating the fleas in all life stages that have already infiltrated your home is much more difficult. Regular prevention and environment control will help protect your cat from fleas, and their ulcer should resolve once the trigger is handled.
  • Food allergies — A six- to eight-week dietary trial may be necessary to determine if your cat has food sensitivities. At the end of the trial, the potential allergenic ingredient is reintroduced, and if your cat has an allergic reaction, the food is causing the ulcer. A switch to a hypoallergenic diet typically resolves these eosinophilic ulcers.
  • Feline atopy — If ulcers persist or recur despite proper flea prevention and lack of known food allergies, feline atopy is typically the cause. An environmental allergy is best diagnosed by intradermal allergy testing, and then using the results to create immunotherapy (i.e., a vaccine for allergies) for your cat.

In some cases, the ulcer will completely resolve on its own. Steroids can often help speed the matter along, and antibiotics will take care of a secondary bacterial infection. However, if the underlying cause is not addressed, your cat may experience frequent eosinophilic ulcers.

Have you noticed an unpleasant sore along your cat’s lips? If so, they may have developed an eosinophilic ulcer. While these ulcers occasionally resolve unaided, you should schedule an appointment with Animal Dental Clinic team to ensure your cat is comfortable and healing well, and to prevent future problems.