QUARTERLY BEAT / OCTOBER 2025
DIAGNOSTIC APPROACH TO THE PRURITIC CAT: Diagnosing FASS in the cat is a diagnosis of exclusion as it is in the dog. Biggest challenges come from difficulty doing diet trials in cats especially in multi-cat households or when owners cannot prevent the cat from roaming outdoors. Some feline owners are also insistent that their cat will not tolerate any diet change or is a “picky eater”. Ectoparasitic control can also be a difficult topic to approach when owners insist that their cat is indoor only and thus could not possibly be exposed to parasites or pollens for that matter. In fact, indoor air quality is almost identical to outdoor air quality so indoor only cats are not exempt from environmental allergies. Looking into the origin of the cat (likely at one point was outdoor, perhaps a stray), other animals that go outdoors and are in contact with the indoor cat, and new cats that have joined the household can serve as a risk factor for Demodex gatoi or fleas. Dermatophytosis should also be excluded as some cats with ringworm can be pruritic due to the cutaneous inflammatory response. TREATMENT The approach to treatment in the allergic cat is similar to that of the dog, however, there are limited options for medical management of pruritus that are FDA approved for use. Antihistamines, glucocorticoids and cyclosporine are often used extra-labelly. Atopica® liquid is the only licensed medication for the treatment of FASS in cats and can offer good relief of symptoms but generally requires daily administration initially and has a lag period before improvement is seen that lasts 3-4 weeks. Once symptoms are controlled, tapering to every other day may be possible. Compounded cyclosporine in the form of flavored chewables, liquids or smaller capsules can be given to cats who are challenging to medicate. Oclacitinib (Apoquel®) has shown efficacy in reducing clinical signs in a few limited studies in cats with FASS; however, is not labelled for use in cats and should be used with caution due to narrow margin of safety in cats. If used CBC and biochemistry analysis is warranted. Lokivetmab (Cytopoint®) is not recommended for use in cats due to the potential for severe adverse reactions to this foreign protein (caninized monoclonal antibody).
Allergen-specific immunotherapy remains my treatment of choice as a targeted, long-term, drug-free option. The goal of immunotherapy is to manage the symptoms without daily chronic medications that often carry side effects. The added benefit of not having to catch a cat daily for oral medications is often appealing and provides a better quality of life for the owner and the cat. Intradermal testing is performed to identify specific allergen reactivity, however, can be challenging due to transient and weak reactions. Serologic testing is frequently utilized either alone or in combination with intradermal testing. Studies on the efficacy of immunotherapy in cats are also limited, however, I have had good success with immunotherapy with decreased need for chronic medications and fewer allergic flares over time. Subcutaneous immunotherapy is well-tolerated in most cats. Transdermal immunotherapy is a newer mode of administration and is very well-accepted by most felines and has shown good efficacy so far (Alibre TM Animal Inc). Sublingual immunotherapy is less often chosen due to the need for once to twice daily administration but is a good option for some owners. While beginning immunotherapy, low-dose alternate day glucocorticoids or Atopica® liquid is used to provide relief of pruritus. Antihistamines provide little relief alone in the majority of cats but may provide steroid-sparing effect in some cats.
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