Eosinophilic Granuloma Complex (EGC) comprises three related conditions that affect cats, causing ulcers or swellings of the skin and mouth. Although their cause is not completely understood, the conditions are mediated by the cats own immune system.

Cause
The cause of Eosinophilic Granuloma Complex is unknown and can affect cats of any age, breed, or sex. Most commonly the first appearance of the disease will occur while the cat is still young or middle-aged. The lesions produced by EGC contain large numbers of active eosinophils, a type of immune cell normally associated with allergies and parasitic infections. Many cats with EGC have underlying allergies that may contribute to the development of EGC. Some researchers suspect that EGC is an autoimmune disease and may have a genetic origin. It is also possible that the cause of each of the three types of lesions seen with EGC may be different.

Types of Lesions
Three different kinds of lesions can be caused by Eosinophilic Granuloma Complex. It is possible for a cat to have more than one type of lesion.

An indolent ulcer (rodent ulcer) is a moist, reddish-brown ulcer that usually occurs on the upper lip. They can be found less commonly on other parts of the lip or inside the mouth. The indolent ulcer is painless and does not itch. Indolent ulcers are most common in middle-aged cats.

Eosinophilic plaques are moist, reddish, thickened, round or oval skin lesions usually found on the abdomen or inner thighs. They are intensely itchy.

Eosinophilic granulomas (linear granulomas) have different appearances depending on location. When found on the surface of the skin, they appear as line-shaped, hairless wounds or ulcers. Linear granulomas are most commonly found on the backs of the thighs of young cats, but can also occur on the face or the feet. They are painless and do not itch. Granulomas of the chin or lip do not always ulcerate but may simply appear as a swollen area with no other symptoms. Granulomas that occur inside the mouth appear as white spots or swellings. The presence of numerous granulomas in the mouth can cause difficulty eating.

Diagnosis
Diagnosis of EGC is achieved by biopsy of the lesion or lesions. Microscopic examination of the tissue will reveal the presence of eosinophils and other characteristic changes associated with EGC.

Treatment
The first step in treatment is to identify and control any possible underlying diseases that may be contributing to the problem, such as allergies or parasites. Remission of EGC lesions is often possible using treatment with drugs that suppress or modulate the immune system, such as corticosteroids. Prognosis is good, however, lesions may recur.