Eosinophilic Granuloma Complex (EGC) represents the way a cat's skin reacts to a variety of offending factors and include feline indolent ulcer (rodent ulcer, eosinophilic ulcer), eosinophilic plaque, and eosinophilic granuloma (linear granuloma). Each abnormality may appear alone or in any combination with 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-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 functions, such as genetic background and stress, may also play a role, since all of the skin problems grouped under EGC show evidence of immune system activation.
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), but can occur anywhere on the body. These 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. Indolent 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 middle-aged female cats are more frequently affected. 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.
Eosinophilic plaques are raised, well-defined, reddened areas with a raw surface that may ooze tissue fluids. They may occur anywhere on the body and usually range in size from about 1/4 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 predisposition 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.