The Classic Comprehensive Handbook of Cat Care
What to Do When Your Cat Is Sick: EOSINOPHILIC GRANULOMA COMPLEX (EGC)
The eosinophilic granuloma complex (EGC) consists of three different-looking skin abnormalities that have been traditionally grouped together by veterinarians as if they represented different manifestations of a single disease. In fact, these skin lesions, feline indolent ulcer (rodent ulcer, eosinophilic ulcer), eosinophilic plaque, and eosinophilic granuloma (linear granuloma) do not represent a single disease but the way a cat’s skin reacts to a variety of different primary problems. Each abnormality may appear alone or in any combination with the others depending on the individual cat’s response to the initiating factor(s). For the most part, the skin problems seen with EGC seem to be related to allergy-induced or parasite- (e.g., flea or mosquito bite) induced skin disease. In some cases viruses such as feline leukemia virus or bacteria have been associated with forms of EGC. Factors that affect general immune system function such as genetic background and stress may also play a role, since all of the different skin problems grouped under EGC show evidence of immune system activation when a skin biopsy (surgical removal of a small piece of skin for a pathologist’s evaluation) is taken and examined under a microscope.
FELINE INDOLENT ULCERS
Indolent ulcers are usually found on the upper edges of one or both lips, most often in the area that overlies the canine (cuspid teeth). They can, however, occur anywhere on the body. Indolent ulcers are usually oval shaped with a depressed area in the center and a raised edge. The surface is raw and bright pink to red but may look brownish if a crust (scab) has formed on the surface. Although the surface looks eroded, the skin in the affected area often feels thickened. These ulcers do not normally seem to cause the affected cat any discomfort. Both young and old cats of either sex or any breed may develop indolent ulcers, but most are seen in middle-aged female cats. It is not unusual for cats with indolent ulcers to also have eosinophilic plaques and/or linear granulomas.
Eosinophilic ulcers alone are sometimes no more than a cosmetic problem for the affected cat, and small areas that are unaccompanied by other signs and do not seem to enlarge may be left untreated. Most indolent ulcers slowly enlarge and deepen if left untreated, and, in rare cases, they can undergo malignant transformation and become cancerous.
So diagnosis of the cause and treatment of the ulcer is always best for the cat.
FELINE EOSINOPHILIC PLAQUES
Eosinophilic plaques are raised, well-defined, reddened areas with a raw surface that may ooze tissue fluids. They may occur anywhere on the body or in the mouth of the affected cat, and they range in size from about one-quarter inch (about 6 mm) to several inches in diameter. Cats lick and scratch at eosinophilic plaques as they seem to be associated with intense itching. Most affected cats are at least two years old, and there is no breed or sex predilection for developing this skin abnormality. In areas where fleas are prevalent, eosinophilic plaques found on the abdomen, rump, and groin are often associated with flea bite allergy.
FELINE EOSINOPHILIC GRANULOMAS
Eosinophilic (linear) granulomas are well-defined reddish to yellow colored, raised skin areas that may appear anywhere on the body or in the mouth of affected cats. Although the abnormal areas may be linear in shape, they also often form firm bumps in the skin. Most linear granulomas are found on the posterior surface of the hindlegs. Another common site is the chin. They are often found incidentally during physical examination, since eosinophilic granulomas are rarely associated with discomfort, and they often seem to wax and wane in size even if untreated.
TREATMENT OF EGC
As with other skin conditions of cats, treatment for EGC is most successful when the cause of the problem is found and removed. Since all of the skin abnormalities in this group have been associated with allergy, attempts should be made to rule out fleas and other skin parasites, foods, and inhaled allergens as triggers for the skin reaction or repeated problems will be likely. Keep your cat clean and practice good flea control.
If you or your veterinarian suspect food allergy, you will need to feed a restricted diet for at least four weeks to discern any positive response.
Most cases of EGC will not respond to simple home care, since the skin abnormalities represent a reaction to long-standing stimulation of the immune system. Your veterinarian may prescribe corticosteroid drugs (e.g., prednisone), fatty acid supplements, and/or antibiotics to treat certain cases. For some difficult cases, immunomodulating drugs other than corticosteroids are used, but most good veterinarians prefer to avoid them due to their potential for serious side effects. To this end most veterinarians will perform diagnostic tests such as complete blood counts (CBCs), skin biopsies, and skin testing in addition to physical examination in an attempt to choose the best treatment and rule out conditions involving the skin which may mimic EGC, such as cancer. Treatment for complicated cases include hyposensitization, surgery, radiation, and laser therapy. Consult a veterinarian specializing in dermatology if your cat has skin abnormalities typical of EGC that do not respond to standard treatment.