Eosinophilic granuloma complex lesions occur when large numbers of eosinophils invade the dermal tissue. The epidermis is also commonly ulcerated or eroded. Eosinophils are white blood cells which are often associated with allergic and parasitic problems but it is unclear exactly what makes them invade the tissue abnormally in this disease.
There are three distinct syndromes involved in eosinophilic granuloma complex, these are: indolent (rodent) ulcers, eosinophilic plaque and eosinophilic granuloma. Eosinophilic plaques are hairless, possibly moist, red and angry looking lesions which may occur on the perineal, inguinal, and axillary regions as well as the thighs. Indolent ulcers occur on the upper lips and they usually have a raised and ulcerated appearance. Eosinophilic granulomas may appear anywhere on the body but are most commonly seen on the lips and in the mouth. The pads of the feet are also commonly affected. If these lesions affect the lower lips the cat may look as if it is pouting since the lips are swollen. If the lesions extend into the mouth the cat might not be able to eat properly, may have smelly breath and drool saliva. On the feet these lesions will cause swelling of the foot pads and the cat may be lame. It is often the case that more than one type of lesion will be present in affected cats at the same time. If it is necessary to distinguish between them it will probably be necessary to take a biopsy for histopathology.
These lesions are undoubtedly painful for the cat but luckily they usually respond very well to treatment. Treatment usually involves administering steroids. This may be given as an injection or orally. The most commonly used drugs are Depomedrone (a long lasting injection) and prednisolone tablets. It is important to monitor animals on these drugs and your vet will want to use the lowest dose possible to manage your pet's condition because these drugs can have serious side effect in long term use. Sometimes antibiotics are also required and in occasional cases may even be effective if used without steroids. It is often necessary to prevent the cat grooming these lesions which in many cases will irritate them further and give them little time to heal; buster collars or bandages may be used to facilitate this. It may be a good idea to have your cat tested for FeLV and FIV because skin disease may be associated with these viruses.
The eosinophilic granuloma complex is believed to be due to an allergic response but there may be genetic factors which predispose individuals to the disease. If an allergy which causes this to occur can be identified and controlled then it may be possible to prevent recurrence of the problem. Common allergies in cats are to fleas, food and other environmental allergens such as pollens and house dust mites. You may find that this problem is a seasonal one for your pet due to the presence of specific allergens at different times of year.
The signs of this disease may come and go spontaneously even without treatment. Unless you can identify a causative allergen and completely prevent your cat being exposed to it (which in many cases will not be possible) the problem is likely to return at unpredictable intervals. Due to the risk of side effects from long term steroid use you may wish to refrain from treating the condition unless the cat shows signs of discomfort associated with it.