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 parasites. 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.
The eosinophilic granuloma is an incompletely understood condition. For now it is best to view it as an extreme symptom of allergic skin disease. The cause of EGC is unknown; however, an underlying hypersensitivity such as a food allergy, atopy, or insect allergy (particularly to fleas and mosquitoes) often has been associated with these lesions. There are no breed predilections to EGC, but females may be predisposed to development of lesions. Young to middle-age cats usually are affected (average age 3.5 years).
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:
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the indolent ulcer
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the eosinophilic plaque
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the eosinophilic granuloma
These conditions are felt to have an underlying allergic basis though it is not always possible to determine what the allergen is.
The skin conditions listed above should be considered “reaction patterns” rather than diseases in and of themselves. What this means is that they are not diseases themselves but symptoms of some other underlying disease (usually allergy).
THE INDOLENT ULCER (“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. Tongue lesions are usually somewhat deep inside the mouth. 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.
Although, most indolent ulcers occur unilaterally on the upper lip, they also may appear bilaterally in the oral cavity or in other cutaneous locations. Typically, the lesions are well-circumscribed with a raised margin and appear red-brown, alopecic, and glistening. These ulcers are painless, non-pruritic, and do not bleed.
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Feline indolent ulcer (rodent ulcer) of the upper lip
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Feline indolent ulcer (rodent ulcer) of the upper lip
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THE EOSINOPHILIC PLAQUE
This lesions typically look like a raised thickened raw area of skin usually on the belly, inner thigh, anal, or throat area. They are well circumscribed, raised, round to oval, erythematous, moist, and often ulcerated. Pruritus (itchiness) usually is severe. A microscope slide pressed onto the affected area often shows numerous eosinophils, thereby confirming this condition. Cats with this condition generally have increased circulating eosinophils in their bloodstreams as well.
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Eosinophilic plaques of the medial thighs and groin
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Throat area eosinophilic plaque
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THE EOSINOPHILIC GRANULOMA (“linear granuloma”)
The eosinophilic granuloma produces a classical swollen lower lip or chin, lesions in the oral cavity (particularly the tongue and palate), or a classical long, narrow lesion running down the back of the thigh. The lesions are typically well-circumscribed, raised, firm, alopecic, erythematous, and non-pruritic. Sometimes proliferations grow from the actual footpads where they ulcerate as the cat walks on them. There is some tendency for this condition to occur in adolescent kittens though it can occur at any age.
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Pink lower lip swelling represents the eosinophilic granuloma
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Eosinophilic granuloma of the digit
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Oral eosinophilic granuloma
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In most cases, the eosinophilic granuloma responds to cortisone-type medications. Typically an injection of long acting corticosteroid (such as Depomedrol) is given and most lesions resolve with one or two injections. As long as such treatment is needed only once or twice a year for recurrences, additional medications or diagnostics are not needed.
If these lesions are not responding to treatment, biopsy may be needed to confirm the diagnosis of eosinophilic granuloma. Tumors or other ulcerative lesions may mimic the eosinophilic granuloma complex. Biopsy may also elucidate less obvious underlying causes such as
demodex mites or
ringworm fungi. After a diagnosis is confirmed, treatments that might be employed include:
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A more aggressive steroid course (i.e. 3 depomedrol injections given two weeks apart).
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A trial course of aggressive flea control and avoidance of mosquitos.
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A food allergy diet trial to determine if food allergy is the underlying source of inflammation.
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Intradermal skin testing for airborne allergy.
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A trial course of antibiotics.
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A trial course of cyclosporine. Cyclosporine has assorted anti-inflammatory properties which could be of benefit.
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Chlorambucil in combination with steroids. Chlorambucil is a drug used against unwanted white blood cell infiltrations including cancers and inflammatory conditions. It should be saved as a last resort.
Other treatments that have been used when other options have failed include:
doxycycline (an antibiotic with anti-inflammatory properties), 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).
