Merck Manual

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Pet Owner Version

Eosinophilic Granuloma Complex in Cats


Stephen D. White

, DVM, DACVD, University of California, Davis

Reviewed/Revised Aug 2018 | Modified Oct 2022

This group of skin conditions affects cats, dogs, and horses. Eosinophilic granuloma complexes have varying signs but seem to be caused most commonly by an allergic hypersensitivity.

In cats, three diseases have been grouped in this complex. Eosinophilic ulcers (also called "rodent ulcers" or indolent ulcers) are well-defined, red, skin ulcers that are usually not painful or itchy. They are most commonly found on the upper lip. Progression to squamous cell carcinoma is extremely rare, although it can occur. Eosinophilic plaque, a well-defined, red, raised wound, is most commonly found on the belly and thighs. It is extremely itchy, and cats will scratch and rub the affected sites. These lesions are often infected with bacteria, which usually make this condition worse. Eosinophilic granulomas are raised, circular, yellowish to pink nodules. They may be found anywhere on the body but are most common on the head, face, bridge of the nose, ears, paw pads, lips, chin, mouth, and thighs. Linear lesions are found most often on the thighs but have been seen on other body locations.

This complex can be due to insects (especially fleas), dietary and environmental allergies, infectious agents, and genetic or hereditary factors. The cause cannot be identified in some cats. Allergies should be investigated by initiating strict flea control, allergy testing, and dietary elimination trials. Some cases will be better defined by having additional laboratory testing performed, including skin cytology, cultures, and skin biopsies. All forms of this complex can often benefit from antibiotic treatment. Many treatment options exist depending on the underlying cause. In cases where the underlying problem cannot be identified or controlled, treatment with corticosteroids or cyclosporine may be required.

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