Eosinophilic Granuloma Complex (EGC) is not a specific disease. Instead, the term is used to describe three types of skin lesions that occur on cats. The cells involved in the pathology of the lesions (eosinophils) and the mass that is comprised of them (granuloma) lend the condition its name. The lesions can occur anywhere on the cat’s body, and their location and appearance differentiate them into three groups: indolent ulcers, eosinophilic plaques, and eosinophilic granulomas.
There may be numerous causes of EGC, and the exact mechanism of their formation is not completely understood. Eosinophils are white blood cells that are involved in allergic and inflammatory responses. They phagocytize (consume) antigens contained in bacteria, parasites, and viruses. EGC is thought to be immune mediated, and may occur in response to hypersensitivities to insect bites (mosquitoes), food allergies, and inhalant allergies. The lesions can mimic many other dermatologic conditions, and because treatment will include the use of immunosuppressive drugs, other disease processes must be ruled out. The presence of large numbers of eosinophils on a biopsy, and a typical clinical appearance of the lesions confirm a diagnosis.
Indolent ulcers, misleadingly nicknamed rodent ulcers, most often occur on the inside of the upper lips. They are not associated with rodents at all. The tissue will be inflamed, raised, and smooth. The ulcers can occur on one or both sides of the mouth. In the case of indolent ulcers, biopsy is usually not diagnostic, but it is used to rule out neoplasia (cancer) when non responsive to treatment.
Eosinophilic plaques can occur anywhere on the skin, but are most often found on the inner thighs and groin. They appear as raised, round, bright red, and hairless masses that are especially itchy. The lesions are ulcerated from self-trauma and may become secondarily infected by bacteria. The circulating eosinophil count in the blood stream will probably be elevated.
Eosinophilic granulomas are found between the toes, on the tongue, and on the roof of the mouth. These ulcerative lesions are raised and crusty on the skin, and erosive in the mouth. They are bright red and may bleed easily. They are not thought to be itchy, but cats may cause self-trauma from over grooming the skin lesions and may stop eating if the lesion is in the mouth. Eosinophils will be elevated in circulation and prevalent in the biopsied tissue.
Treatment for EGC begins by ruling out and treating any underlying disease that may be a contributing factor. Secondary bacterial infection is addressed with oral and topical antibiotics. An Elizabethan collar may be used to prevent self trauma. Immunosuppressive drugs like prednisone and other steroids are prescribed specifically for EGC, and may be given for weeks until response is seen. A tapering or pulse dosing is sometimes required to prevent recurrence of the lesions.
For EGC that responds poorly to steroid therapy, immuno-modulating drugs may be used. Certain antibiotics have this effect, and may be prescribed for 2 to 4 weeks. Chlorambucil is the most common immuno-modulator drug used in refractory EGC.
Omega fatty acid supplements may also improve lesions to some degree. They may reduce the steroid dose required during treatment, decreasing the chance of side effects from these drugs.
In very young cats, EGC lesions may spontaneously resolve without treatment. The prognosis for older cats is more guarded, and they may require on going steroid therapy to keep the lesions in remission.