Eosinophilic Granuloma Complex
The eosinophilic granuloma complex is a group of diseases that appear to be related. They are distinct lesions on the skin that response to the same treatment. They are somewhat misnamed because not all of them have eosinophils present.
Eosinophils are normal blood cells that are part of the body's immune system. Their number increases in certain diseases, including allergies and parasites. They are also found in high numbers in other diseases but are typically not related to cancer.
There are three rather distinct diseases in the eosinophilic granuloma complex: 1) rodent ulcer, 2) eosinophilic plaque, and 3) linear granuloma.
A rodent ulcer (indolent ulcer) begins as an ulcerated area on the upper lip between the large canine teeth. As it increases in size, the upper lip may become swollen and very painful. It is name a "rodent" ulcer because there was a belief that mice and rats were biting the cat's upper lip as they were being attacked. However, this problem has nothing to do with rodents.
The eosinophilic plaque is a round to oval area on the skin that is very red and inflamed. Hair is often lost over the area possibly due to licking by the cat. These lesions may be 1" to 4" across and usually occur on the ventral abdomen (belly). They are often accompanied by smaller lesions on the bottom of the feet and in the mouth.
The linear granuloma is usually a raised, rope-like lesion along the rear aspect of the upper part of the back legs; however, it may occur in other locations as well. It may be 1/4" to 1/2" across and several inches long. It is non-painful, and the hair usually does not fall out around or over it. Owners often find it as they pet or hold their cat.
Each of the three diseases has a characteristic appearance and can often be diagnosed just from that. If the diagnosis is not certain, a biopsy may be performed. A biopsy of the eosinophilic plaque reveals a large number of eosinophils. The other two forms may or may not have eosinophils present but the pathologist can identify other characteristics that make the diagnosis.
Each of these diseases responds well to corticosteroids ("steroids" or "cortisone"). The injectable forms of steroids are usually more effective than steroid tablets. Response should begin within one day and near-recovery should occur within one week. The steroid injection may need to be repeated in 3-4 weeks for a complete response.
Some of these lesions are infected with skin bacteria. Therefore, antibiotics may be part of the treatment.
Many authorities feel that the basis for all of these diseases is an allergic response. The fact that they all respond so well to steroids is one of the evidences given. Allergies usually respond well to steroids. A cat with a rodent ulcer may be having a contact allergy to the food bowl. There are anecdotal reports of cure just by changing from plastic bowls to glass, porcelain, or stainless steel bowls. Since this is a simple thing to do, it probably should be tried if your cat eats or drinks out of a plastic bowl.
Unfortunately, most of these diseases recur when the injection of steroids has dissipated; this usually takes 3-4 weeks. Repeated injections may be needed. Many cats can be controlled long-term with oral steroids if the tablets are preceded by an injection.