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Q. What are your tips for diagnosing and treating atopy in cats? Are cats typically sensitive to some allergens more than
A. Pruritic cats usually have one of four problems:
Dr. Ian B. Spiegel
1. Flea bite hypersensitivity
2. Cutaneous adverse food reaction
3. Environmental allergies (atopy)
4. Ectoparasites other than fleas (e.g. mites).
RULING OUT OTHER CAUSES OF PRURITUS
Flea allergy dermatitis is the most common cause of feline pruritic disease. Strict flea control on all animals every month is important to rule this out as the sole cause of the pruritus. Other ectoparasitic causes must be ruled out as well (e.g. Cheyletiella, Notoedres, Otodectes, and Demodex species). Whether or not these mites are detected (by evaluating samples obtained by skin scraping, hair plucks, or combing),
several treatments are indicated to simply rule these out as causative factors for the pruritic disease. A broad-spectrum
topical spot-on parasiticide (selamectin or moxidectin) is usually helpful. Lime sulfur is also an option.
Tests for cutaneous adverse food reaction (food allergies) are available as well. However, these food allergy tests are not
usually indicated; clients are better served investing in an elimination diet (novel protein or hydrolyzed diet). Cutaneous
adverse food reaction is more common in cats than in dogs and should be strongly suspected when a cat is presented for gastrointestinal
signs and primarily facial dermatitis (despite parasite control).
GETTY IMAGES / LISA STIRLING
DIAGNOSING FELINE ATOPY
As with dogs, horses, and people, the most common environmental allergens causing clinical signs are house dust or house dust
mites. Other common allergens include weeds, grasses, trees, and molds, even if a cat is an indoor cat. Diagnosing feline
atopic dermatitis is usually a process of elimination. Allergy testing is not necessarily a diagnostic tool for atopic dermatitis;
it is a test that is indicated when a client is interested in immunotherapy. One could make the argument that allergy testing
is indicated for avoidance, but this is difficult in many cases.
Serology or intradermal testing can be performed when trying to determine which allergens should be incorporated into the
immunotherapy formulation. Skin allergy testing is more challenging in cats as compared with dogs. The reactions seem to be
more immediate and less prominent, with variability in erythema and wheal formation. In my opinion, intradermal (skin) testing
would usually be the superior option in dogs and horses, while in cats, I usually perform a serology test initially.
Now, the frustration for many is the frequent negative results when allergy testing or the reluctance for clients to choose
immunotherapy. A negative test result does not rule out atopic dermatitis. A subset of patients will not have positive results
even with multiple intradermal tests or serology tests. For these patients, which are said to have intrinsic atopic dermatitis, immunotherapy is usually not an option. However, there is research looking at regionally specific immunotherapy, or immunotherapy
based on the most common allergens in a particular region without relying on allergy test results.