Feline Atopic Dermatitis
Feline AD is similar to canine AD. It is a pruritic disease in which affected cats have a hypersensitivity reaction to inhaled or contacted environmental allergens. The age of onset is variable but generally is <5 yr. The signs may be seasonal or nonseasonal. Purebred cats may have a higher risk than domestic shorthaired cats. As in dogs, pruritic cats may have several clinical presentations (eg, miliary dermatitis, symmetric alopecia, eosinophilic granuloma complex, head and neck pruritus) that are consistent with a diagnosis of AD but that must be differentiated from other diseases with similar clinical signs. Differential diagnoses include flea allergy, various mite infestations (eg, Cheyletiella, Demodex, Notoedres, Sarcoptes, Otodectes), mosquito bite hypersensitivity, food allergy, autoimmune disease (eg, pemphigus foliaceus), dermatophytosis, and cutaneous neoplasia. A thorough review of the cat’s history and complete dermatologic and physical examination, along with the standard flea combing, skin scrapings, and fungal cultures, are mandatory first steps. The diagnosis of AD is made when the other differential diagnoses have been eliminated. Response to glucocorticoids is excellent initially but decreases over time.
Intradermal allergy testing and hyposensitization procedures in cats are similar to those used in dogs, but the intradermal test results are more difficult to read because the reactions are less dramatic and dissipate more rapidly in cats. The same avoidance recommendations made for dogs apply to cats. Symptomatic therapy includes control of secondary infections and use of antipruritic drugs. The approved formulation of cyclosporine for use in cats is liquid; the dosage is 7 mg/kg, and it can be administered PO or in food. After 30 days, the dosage can be tapered to every other day in ~70% of cats and to twice a week in ~50% of cats. Response to immunotherapy is similar to that in dogs (see above); owners are advised to commit to 1 yr of therapy before deciding its usefulness.