Feline Eosinophilic Granuloma Complex

What is a granuloma?
A granuloma is a solid grouping of inflammatory cells coming together in a lump or solid structure.

What is an eosinophil?
An eosinophil is a type of white blood cell that is commonly associated with allergic responses or with parasitism.  The eosinophil has a characteristic appearance under the microscope due to the presence of pink staining granules. Finding eosinophils in tissue suggests allergic disease usually whereas finding increased eosinophil numbers in a blood sample more commonly suggest parasitism.

So what is Eosinophilic Granuloma Complex?
Given the above information it would seem logical that an eosinophilic granuloma would be a granuloma made up of eosinophils; however, the situation is more complicated. Initially, it appeared that eosinophilic granuloma was just what it sounds like but as it was studied more thoroughly, it was found that there were three different types of this condition and not all were granulomas and not all involved eosinophils.

There are three separate skin conditions making up the Eosinophilic Granuloma Complex and a cat may have any or all of them. These three conditions are called:

Ø      indolent ulcer

Ø      eosinophilic plaque

Ø      eosinophilic granuloma

These conditions are felt to have an underlying allergic basis though it is not always possible to determine what that allergic basis might be.

Indolent Ulcer (also called "the rodent ulcer")
Cats with indolent ulcers have an erosion on the margin of their upper lip. Sometimes, a proliferative eroded structure also develops on the tongue so if your cat has a classical lip ulcer, it is a good idea to open the cat's mouth and check the tongue yourself. Tongue lesions are usually somewhat deep inside the mouth as shown. In general, the appearance of the indolent ulcer is classical and a biopsy is not needed; though occasionally these are precancerous conditions and biopsy may be needed to rule out a malignant skin tumor.

classic  rodent ulcer                Lesion on foot pad

Eosinophilic Plaque:

This lesion typically looks like a raised thickened raw area of skin usually on the belly, inner thigh, or throat area. Cats with these lesions are commonly extremely itchy. A microscope slide pressed onto the affected area often picks up numerous eosinophils which can be detected under the microscope thus confirming this condition. Cats with this condition generally have increased circulating eosinophils in their bloodstreams as well.

Eosinophilic Granuloma (also called the linear granuloma)
The eosinophilic granuloma produces a classical swollen lower lip or chin or a classical long, narrow lesion running down the back of the thigh. Sometimes proliferations grow from the actual footpads where they ulcerate as the cat is forced to walk on them. There is some tendency for this condition to occur in adolescent kittens though it can occur at any age.

What is happening to these cats?
The eosinophilic granuloma complex represents a disorder of eosinophil function. The eosinophil's real job is to attack parasites. It is designed to be attracted to areas where parasitism is occurring and once there it releases special biochemicals to destroy the invading creature. In cats with eosinophilic granuloma complex, eosinophils are called to the site of an allergic response and the biochemicals released cause damage to local collagen.

How do we treat this problem?
In most cases the eosinophilic granuloma responds to cortisone derivatives though often an aggressive regimen must be used. Typically an injection of long acting corticosteroid (such as Depo-medrol) is given every 2-3 weeks until the lesion is gone

or for three injections whichever comes first.

Most eosinophilic granulomas resolve with one injection but some are refractory and will not resolve until antibiotics are used. Some are more refractory still and require more exotic treatments. Hormones (such as Ovaban tablets and depo provera injections) were once widely used for this condition but are now considered last resorts due to side effects potential (they can cause diabetes mellitus and can raise the risk of mammary cancer).

It is important to realize that this is a recurring condition that frequently has an allergic basis.  This means that it is a good idea to look for an obvious allergen in the pet's environment and attempt to eliminate it. The most common allergy in the cat is flea bite allergy so flea control should be immaculate for an eosinophilic granuloma complex kitty. If the cortisone derivative response is poor, it may be prudent to look into food allergy, as food allergy is often not cortisone responsive.

The eosinophilic granuloma is an incompletely understood condition. For now it is best to view it as a symptom that can occur with allergic skin disease.