To be sure FAD does not accompany an additional skin problem, make sure the patient and environment are treated for fleas faithfully for at least one month, then reassess whether the cat is still pruritic. If so, additional differentials for pruritus need to be pursued. Inhalant allergy Inhalant allergy or atopy is a relatively newly recognized disease in the cat. It is defined as an inherited exaggerated IgE response to inhaled or percutaneously absorbed antigens. To date, feline IgE has not been isolated and identified.
Some atopic cats have an accompanying peripheral lymphadenopathy or circulating eosinophilia.
If pruritus remains once any ectoparasite infestation has been addressed for at least four to six weeks, dermatophytosis has been ruled out via a fungal culture, and food allergy has been ruled out by feeding a hypoallergenic diet for four to six weeks, intradermal skin testing or in vitro testing is then performed to determine which allergens are needed in the hyposensitization solution. Hyposensitization is quite successful in cats, probably since most have had other differentials ruled out so as to rule in atopy in a truly atopic cat. In my practice, a large percentage of atopic cats are house dust mite allergic, probably because the majority of cats we see are strictly indoor cats and have become sensitized to indoor allergens. Also, false negative in vitro test results can occur if the patient is not withdrawn from its previous steroid therapy for a long enough period of time. Some patients may test positive when off steroids for a month, others require three to four months.