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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. Eosinophil counts will go up on a blood test when a pet has fleas or worms or when an allergy is flaring up. Eosinophils can circulate in the blood or they can infiltrate tissue. They are part of the immune system and are “on patrol” for biochemical signals from tissue (calls for help, if you will) telling them that a parasite has invaded. Eosinophils home to the signal and release chemicals to attack the parasite. Unfortunately, they can be tricked into thinking that some sort of benign materials (pollens, dust, etc.) are attempting invasion. In this instance (allergy) they release their inflammatory chemicals inappropriately, creating the sensations of itching, swelling, redness and other symptoms of allergy.
The eosinophil has a characteristic appearance under the microscope due to the presence of pink staining granules. The pink staining granules contain assorted toxins and biochemicals designed to attack an invading parasite. These granules can be thought of as small bombs directed against large invading organisms such as worms.
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 classes of this condition and not all were granulomas and not all involved eosinophils. Further, the name "eosinophilic granuloma" implies a final diagnosis but this is generally not the case. Eosinophilic granuloma lesions are more like symptoms of a variety of underlying causes such as allergy or even bacterial infection.
The three classes of Eosinophilic Granuloma Complex are listed below and an individual cat may have any or all of them. The three classes are:
These conditions are felt to most commonly have an underlying allergic basis though it is not always possible to determine what that allergic basis might be. The presence of any of the three above conditions does not definitively imply any specific type of allergy. In fact, there is some evidence that some cases begin as simple allergic reaction to an external substance but when internal skin proteins are released by scratching, the reaction continues to involve these “self” proteins as well.
THE 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.
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. If allowed to go untreated, the ulcer can be very destructive to the upper lip. Even after treatment, the ulcer will likely heal but the area of lip that has been destroyed will not grow back and the cat's face will be permanently altered.
YumYum gives us an example of a “Rodent Ulcer”
THE EOSINOPHILIC GRANULOMA (also called “the linear granuloma” or "collagenolytic 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 EXACTLY 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. As mentioned, the reaction can include “self” proteins as well as external ones. It is important to realize that the Eosinophilic granuloma patterns, as specific as they can be, do not point to a specific cause. The most common cause is some kind of allergy and treatment is generally directed to attempting to determine the specifics of the allergy and suppress the immunological excess reaction.
Other treatments that have been used when other options have failed include: doxycycline (an antibiotic with anti-inflammatory properties), gold therapy (yes, oral medications using gold have been used with mixed success in inflammatory conditions), removing the lesion via laser or cryotherapy, and daily high dose interferon alpha.
Female hormones (such as Ovaban® tablets and Depoprovera® injections) were once widely used for this condition but are now considered inappropriate due to side effect potential (they can cause diabetes mellitus, pyometra, and can raise the risk of mammary cancer). They would be considered a last resort.
The eosinophilic granuloma is an incompletely understood condition. For now it is best to view it as an extreme symptom of another underlying skin disease.
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Page last updated: 10/11/2021