Eosinophilic Granuloma Complex in Cats

What is feline eosinophilic granuloma complex?

Eosinophilic granuloma complex (EGC) is a term used to describe three types of skin lesions in cats: eosinophilic plaques, eosinophilic granulomas, and indolent ulcers.

The exact cause of EGC in cats is unknown. Some research studies suggest that, in most cases, a form of allergic response (hypersensitivity reaction) may be involved, especially in cases that recur. Other studies suggest that the condition may at least be partially genetic or inherited.

What are the clinical signs of EGC?

The most common site for these lesions is the lips, especially the upper lip, where they appear as ulcers. They are sometimes referred to as “rodent ulcers,” because people once thought the lesions were caused by rodent bites, but they are not. The lesions range from small and barely noticeable ulcers to large and extensive ulcers that disfigure the lips. Bleeding occurs from some lesions. Some cats may get a swollen, puffy chin.

Eosinophilic granulomas may also develop in the mouth, especially along the gums and palate, or on other areas of the body. When lesions form in other locations, they usually appear as bald patches with raised areas of reddened skin rather than an ulcer. These lesions are often called eosinophilic plaques. Common sites are the hind legs and the stomach. The lesions can be large and may be itchy, as cats frequently lick and bite the affected areas.

How is EGC diagnosed?

Diagnosis starts with your cat's medical history and physical examination findings. To obtain a definitive diagnosis, your veterinarian may perform a fine needle aspiration (FNA). FNA involves taking a small needle with a syringe and suctioning a sample of cells directly from the lesion and placing them on a microscope slide. A veterinary pathologist then examines the slide under a microscope.

A similar test is also sometimes performed by pressing a microscope slide against a suspected eosinophilic plaque. By examining the imprint under the microscope, numerous eosinophils (a type of white blood cell) may be visible.

In some cases, results from FNA may not be clear, and a biopsy may be necessary. A biopsy is the surgical removal of a piece of the lesion. The characteristic lip ulcers are highly suggestive of EGC, and a biopsy may not be required; however, if lesions are located elsewhere on the skin or in the mouth, a biopsy will rule out other diseases and conditions.

How is EGC treated?

If an underlying cause is identified, treatment will be directed at removing this cause. 

Flea and insect control is very important in the treatment of this condition, because insect bites can trigger an exaggerated immune response in affected cats, causing or worsening clinical signs.

Some cats respond to elimination diet trials or hypoallergenic diets, suggesting an underlying food allergy is the cause. Most cats diagnosed with feline EGC benefit from a hypoallergenic food trial.

Corticosteroids are the most common treatment to control the symptoms of EGC. Corticosteroids are available in different forms with different durations of activity; most often, cats are given oral tablets or liquid preparations. Long-lasting injections may be available if the cat is not willing or able to take oral medications.

Treatment may last for weeks or months because eosinophilic granulomas frequently recur and prolonged treatment minimizes the chance of recurrence. Side effects of corticosteroids are usually not significant in cats, but prolonged use can cause an increase in weight and can predispose the cat to diabetes mellitus (sugar diabetes).

Cyclosporine (Atopica®) is another drug often used in cats to manage allergic skin disease. It acts as an immunosuppressant and is a good alternative for cats that cannot take steroids.

What is the prognosis for a cat diagnosed with EGC?

Most cases respond well to medical treatment and management. Since recurrence is common, life-long intermittent treatment is needed in many cases. Cats that are severely affected will require more aggressive treatment and a referral to a board-certified veterinary dermatologist may be beneficial.