Just Ask the Expert: The best way to address feline atopy
Dr. Spiegel welcome dermatology questions from veterinarians and veterinary technicians.
Q. What are your tips for diagnosing and treating atopy in cats? Are cats typically sensitive to some allergens more than others?
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.
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.