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Eosinophilic Granuloma Complex (EGC) is a group of skin conditions that occurs in cats but rarely in dogs. It is named after a type of white blood cell usually involved with allergic responses, the eosinophil, and it is called complex because of the number of different forms it can take. It originally was thought to only be associated with granulomas (firm inflamed nodules) but it was renamed “complex” when it was learned that the lesions can take other forms, including plaques and ulcers.
Eosinophilic granulomas themselves can take linear form (typically found on the abdomen or the backside of the legs), nodular form in the mouth, or as a swelling on the chin. This presentation can be confused with advanced feline chin acne that has caused chin swelling. The granulomas in all forms are typically red, hairless, raw, and usually not itchy.
Eosiniphilic plaques are round to oval lesions that are irritated, moist, and hairless sores within the skin. They can cover a large portion of the abdomen and thighs but can also appear on other area and are often itchy.
An indolent eosinophilic ulcer (otherwise called a rodent ulcer) occurs as a hairless depression or area of inflammation of the upper lip but other parts of the mouth may be involved as well. They are typically not itchy and can transform into a malignant cancer.
The general appearance of these lesions is often suggestive of the diagnosis, but testing is often needed to confirm. In addition to the physical appearance of the lesions, patients may also exhibit other clinical signs depending upon the type and location of the lesion. Itching, pain, drooling, reluctance to eat (all with oral lesions) or even lameness (with foot lesions) may occur. Sometimes eosinophils are found when smears of the lesions are examined under the microscope called an impression smear. A skin biopsy with histopathology usually confirms the diagnosis. These lesions can resemble some neoplasms (tumors).
Cats of all ages can be affected, but it more often affects younger and middle-aged cats and females are affected more than males.
The underlying cause of EGC is believed to be related to allergies. Allergies cause a release of eosinophils by the body that contributes to EGC over time. In addition, it is believed that there is a genetic link, though this isn't well understood. In many cases, the cause is never known. Possible agents that are linked with the condition include:
Environmental allergens that are inhaled
Food allergies
External skin parasites and insects
Bacterial skin infections
Fungal skin infections
Viral infections such as feline leukemia virus or feline immunodeficiency virus
All presentations of the disease complex require the same basic treatment. If an allergen is identified, you must decrease exposure to that allergen, which is often easier said than done. Antibiotics are needed if the lesion is infected, which is often the case. Most lesions will respond to corticosteroid treatment which helps shrink the lesion. This isn't always effective but other drugs that modify the immune response may be tried when steroids fail.
Small unresponsive lesions may also be treated by surgical removal. Laser therapy is also becoming more widely available for treatment as more general practitioner veterinarians have laser therapy offered for surgery and other procedures. Radiation therapy is also available as an option at advanced facilities. It can take several weeks of treatment before the patient begins to respond. If the patient doesn't respond after one to two months, a biopsy should be performed on the lesion - if that has not yet been performed.
EGC isn't cured and must be managed. Allergy control is important to reduce occurrences. When the insulting allergen can be identified and controlled, EGC has a favorable prognosis. Recurrence is possible when the patient is either resistant to treatment or for patients in which the underlying cause is never identified.