How should feline atopic skin syndrome be diagnosed and managed in a cat with chronic pruritus?

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Feline atopic skin syndrome (FASS) is a diagnosis of exclusion, requiring elimination of flea allergy, food allergy, external parasites, bacterial skin infection, and dermatophytosis before the diagnosis is confirmed. Up to 25–30% of FASS cats exhibit seasonal pruritus, which supports an environmental allergy diagnosis without requiring a dietary elimination trial, provided external parasites and secondary infections have been addressed.3 In the non-seasonal pruritic cat, failure to respond to a strict elimination diet trial is required to implicate FASS.3 Once FASS is confirmed, intradermal or serum allergy testing by a veterinary dermatologist identifies specific environmental allergens for inclusion in allergen-specific immunotherapy (ASIT). Referral to a dermatologist at the point of confirmed diagnosis is recommended, as targeted treatment reduces the client frustration and loss of trust that accompanies empirical therapeutic trials.3 If referral is not possible, establishing a baseline pruritus score before initiating treatment allows objective assessment of therapeutic response.3 Glucocorticoids are first-line for initial pruritus control and serve as a diagnostic test of therapeutic response, given that most allergic cats respond to them.3 When pruritus exceeds 6 out of 12 months per year, long-term alternatives should be discussed with the owner.3 Cyclosporine is the only labeled systemic treatment for FASS in Canada and reaches therapeutic levels at 4–6 weeks, after which dosing frequency can often be reduced to every other day or less.3 Cyclosporine is contraindicated in outdoor cats due to the risk of fatal infectious disease exposure, particularly toxoplasmosis; cats on cyclosporine should be fed a cooked diet and maintained on effective internal and external parasite control.3 Systemic toxoplasmosis has been reported in cats receiving cyclosporine or prednisolone for FASS.5 Oclacitinib (Apoquel, Zoetis) is an off-label Janus kinase 1 inhibitor with dem