An eosinophil is a type of white blood cell that is commonly associated with allergic inflammatory responses or with systemic reaction to parasites. Eosinophil counts will tend to be elevated when a pet has fleas or worms or when an allergic process is at work. Eosinophils can circulate in the blood, infiltrate tissues, or both.
With the skin conditions eosinophilic ulcer, eosinophilic plaque, or eosinophilic granuloma complex, eosinophilic infiltration of skin tissue results in the visible skin lesions. These skin lesions are found almost exclusively in cats, and are not phenomena typically associated with dogs.
One would think given the nature of eosinophilic celluar infiltrates, that these lesions would involve an allergy, parasite, or both. However, the presence of these conditions does not necesssarily signal allergy or parasites, but perhaps a combination of allergy and/or parasites, combined with an abnormal eosinophilic response that is unique to the feline patients that suffer from these lesions.
Eosinophilic Ulcer (also known as Indolent Ulcer or Rodent Ulcer)
Eosinophilic ulcers present in cats as an erosion of the upper lip. These lesions can present on the lower lip as well less commonly, and even on the inner lips, gums, tongue, or some or all of the above.
Eosinophilic plaques present in felines are raised, thickened, red, raw regions of skin most commonly found on belly, under the neck, or on the inner thighs. Realistically, they can appear anywhere on the body.
Eosiniphilic Granuloma Complex
Eosinophilic granuloma complex are skin lesions that present in cats as multiple lesions, in multiple areas of the body. The lesions maintain a raw, red, thickened appearance, but often begin to take on a more mass-like, cauliflower appearance. Common areas include the lips, inner and outer thighs, the foot pads, or some or all of the above.
Diagnosis of any of the three presentations of esosinophilic disease in cats is often acheived by visual inspection, given the hallmark appearance of these lesions. However, it is important to rule out other causes for skin tissue proliferation, such as various skin cancers. For better confirmation of eosinophilic disease of the feline skin, impression smears can be taken by pressing a microscope slide on the lesions and checking under the microscope for typical eosinophilic cellular infiltrate. If there is any doubt or the veterinarian prefers conclusive diagnosis, confirmation can be obtained by tissue biopsy, where a sample of the lesion is sent to a lab for histopathology.
Eosonphilic skin disease in cats is often treated with corticosteroids, typically with favorable results. However, rodent/indolent ulcer, eosinophilic plaque, and eosinophilic granuloma complex frequently return, necessitating future repeat treatment. Depending on the severity of eosinophilic disease, this could be one to a few times yearly, monthly, or even constant.
If disease is frequently repeating, it may be useful to rule out underlying catalysts for esosinophilic skin disease, such as food allergy, environmental allergy, and fleas. Respectively, these underlying diseases can be ruled out by hypoallergenic food trial, blood or intradermal skin testing, and instituting quality flea control.
Roger L. Welton, DVM
Founder and Chief Editor, Web-DVM.net
President, Maybeck Animal Hospital
Article updated 10/12/2012