Eosinophilic Granuloma Complex

“Doctor, my cat is itchy, and she has these little bumps all over.”

Frida might have ECG tendencies, but she stays totally indoors, away from predators and allergens, and keeps a high level of flea control with her monthly heartworm preventive.

After a thorough examination, I announced, “Lucy has Eosinophilic Granuloma Complex. We call it EGC.”

Since that first visit, we have treated Snoopy several more times for the condition, and she has responded beautifully.

Board-certified veterinary dermatologists dislike using “EGC” as a diagnosis, preferring to name the individual syndromes:
• mosquito bite hypersensitivity
• eosinophilic plaques
• linear granulomas
• indolent or rodent ulcers

Most general practitioners simply lump the syndromes together under the EGC umbrella. Let’s look at them individually.

The prefix hyper- means “increased.” Therefore, hypersensitivity is a reaction greater than it should be. If a mosquito bites your kitty, there should be an awareness that something happened, and that should be the end of it.
With mosquito bite hypersensitivity, the body responds to the bite with redness, swelling, fluid production, massive numbers of eosinophils locally and in circulation, collagen breakdown and itchiness. The most evident lesion is usually on the bridge of the nose, and ears, but lesions similar to eosinophilic plaques can occur on the trunk, sometimes accompanied by thickening of the footpads.

A plaque is defined by its shape. Think of a flat-topped butte protruding from the landscape in Montana, miniaturize it to 2 mm by 20 mm, put that on your cat, and you have a plaque. Plaques can coalesce to affect a large, raised, moist area. This was Snoopy’s presentation: so many fused plaques that it seemed her entire skin surface was affected.

However, in the earliest stages, miliary dermatitis may be seen before plaques occur. Miliary comes from the Latin root milium, meaning millet. Miliary dermatitis is a pattern of small, raised lesions with crusts resembling millet seed. It is what gives these patients their characteristic gritty feel.

Let’s look at the plaque microscopically. Overwhelmingly, we see eosinophils, white blood cells associated with hypersensitivity. Once activated, eosinophils release powerful chemicals, initiating inflammation and even causing necrosis of collagen protein. The result is sores that come not from the patient scratching itself, but from the violent eruption inside the skin.

We also see bacteria, as infection may be a part of the picture of some eosinophilic plaque patients.

The classic linear granuloma lesion occurs on the back leg(s) of young, female cats. They can be raised, feeling like a cord under the skin, greyish-pink and usually not itchy.
Another form, “nodular” or “localized” can occur on the front of the lower lip, giving the appearance of a bulging chin. They also appear inside the mouth, on the bridge of the nose, ears and feet, including the pads.

When a kitty presents with this lesion, it’s the very first thing his doctor sees. The philtrum, the crevice under the nostrils, will be swollen, red and raw. Pet owners usually ask whether their cat has caused this with his rough tongue, but, no, this is another hypersensitivity lesion that came from inside the body. In severe cases there may be a permanent defect in the lip.
The scariest thing about rodent ulcer, so-named because it makes your kitty look like he has rat lips, is that some kinds of skin cancer can look just like this. Rodent ulcers that fail to respond to treatment should be investigated as possible cancer sites.

For decades, corticosteroids (cortisone-like drugs) have been the firstline treatment for this complex of conditions. For the patient with intermittent lesions, an infrequent steroid injection is the cat’s meow. However, the more steroids a patient is administered, the greater the likelihood of complications, including weight gain, diabetes and kidney disease.
The most common trigger for EGC is insect bites, especially fleas and mosquitos. Maintaining a high level of flea control is your first line of defense. Year-round, use a heartworm preventive that kills and prevents fleas. Treat your house and yard regularly, whether or not you think you have fleas there. Indoor cats have less exposure to both fleas and mosquitos, as well as cars, dogs, diseased stray cats, etc.

There are no safe mosquito repellants available for cats.

Black flies can also be a trigger.

Food allergy is a common finding in EGC patients. It is not an allergy to a brand, but to the protein sources in the food, especially beef, poultry, soy, dairy and egg. Special prescription diets are available for food allergy patients, so pet owners no longer have to cook their own pet foods.

In some patients, bacterial infection can be such a big factor that antibiotics alone may clear an episode.

Many EGC kitties suffer from atopy, an allergic reaction to dust, pollen, mold and certain fabrics. The reaction may occur after direct contact or inhalation of the offending material.

Cause? Drs. Mason and Burton, in A Practical Guide to Feline Dermatology, say, “Despite much recent progress in feline dermatology, the eosinophilic granuloma complex remains poorly understood and is still a source of treatment failure.”

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