Dr. Alice M. Jeromin
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Although the incidence of atopy in cats has been reported to be about l6 percent in past studies conducted at Cornell University
and the University of Georgia, it seems that during the past few years at my practice we've seen an increase in the number
of cats with this disorder. As in dogs, atopy is a diagnosis of rule-outs, and I hope the following discussion will help you
diagnose and, consequently, treat feline atopy.
What is atopy?
Photo 1: Facial excoriation in an atopic cat.
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Atopy is defined as an inherited, exaggerated IgE response to inhaled or percutaneously absorbed antigens. IgE binds to mast
cells, and, on reexposure to the antigen, cross linking occurs, causing mast cell degranulation. The release of other inflammatory
products consisting of histamine, leukotrienes and prostaglandins accounts for the clinical signs.
Photo 2: Facial and ear excoriation in an atopic cat.
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The epidermal barrier also may play a role in establishing atopy in a patient. Atopic cats have increased CD4+ T lymphocytes
in lesional skin, which supports the role of T helper type 2 (Th2) lymphocyte-mediated immunity in feline atopy (similar to
in dogs and people).
Photo 3: Groin erythema in an atopic cat due to excessive licking despite wearing an Elizabethan collar.
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Characteristics of feline atopy differ from those in dogs in that the age of onset is extremely variable—from 6 months to
l4 years old. The Devon Rex breed could be more prone, but there's no definitive breed or sex predilection. However, in our
practice we tend to see atopy more often in orange or orange-color-containing cats, such as orange tabby, calico and tortoiseshell
cats.
No set pattern of signs occurs in cats as it does in dogs, but the face, feet and perineum can be affected (Photos 1-3). On
physical examination, atopic cats may show self-induced alopecia, miliary dermatitis, eosinophilic granuloma complex lesions,
exfoliative dermatitis, chin acne with or without Malassezia otitis, seborrhea, eosinophilia or lymphadenopathy.
Difficult to diagnosis
The signs of atopy can mirror other diseases, such as dermatitis (flea allergy or Malassezia), Cheyletiella or Notoedres species infection, food allergy, dermatophytosis, demodicosis and pemphigus foliaceus. Most atopic cats are corticosteroid-responsive,
but so are cats with the above differential diagnoses. Flea allergy dermatitis, cheyletiellosis, Notoedres species infection, demodicosis and dermatophytosis can largely be ruled out by performing skin scrapings, combings and trichography
during the first appointment.
Taking a good history is essential since atopy tends to affect a patient at the same time every year—this can also be true
for a flea allergy, especially in the Midwest where fleas tend to be eradicated in the cold winters. In a patient with nonseasonal
signs, food allergy or allergy to dust mites should be considered once ectoparasites have been ruled out. Note that some food-allergic
cats can be somewhat corticosteroid-responsive, so response to corticosteroids to rule out food allergy isn't dependable.
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