Pruritus is a common dermatologic problem in cats. In this study, data from cats with chronic pruritus (at least 2 episodes, or >2 months in duration) were analyzed. Investigators recorded signalment, history, and 72 other parameters, including age of onset, lifestyle, food, pruritus intensity, skin lesions and distribution, concurrent clinical signs, outcomes of previous treatment, laboratory test results, and final diagnosis. Minimal required workup included adequate flea control, skin scrapes, and fungal culture. Skin cytology and additional diagnostics (eg, biopsy, laboratory work) were conducted when necessary. Diagnosis was based on at least 1 positive result for a specific test and a positive response to adequate treatment (eg, dermatophyte culture and response to antifungal treatment). The diagnosis of nonflea hypersensitivity was based on lack of response to flea control, lack of response to food trial, and positive response to glucocorticoids, cyclosporine, or antihistamines. While 588 cats presented with pruritus, 86 were excluded because diagnosis was unclear or more than one diagnosis existed. Of the remaining 502 cats, 29% responded to flea control, 24% were diagnosed with a nonhypersensitivity cause, 12% had food allergy, and 20% had nonflea/nonfood hypersensitivity (ie, feline atopy). Cause of pruritus was not identified in 15% of the cats.

Commentary
As the largest case study of pruritic cats published to date, this study has many key take-home points: First, 15% of cats presenting to dermatologists had confounding diagnoses. Second, 29% of cats with chronic pruritus responded to flea control, making a strong case that flea control is a cost-effective treatment trial. Third, 24% of cats had a diagnosis other than allergy as the cause of pruritus; conducting core diagnostics is important—an itchy cat does not always equate with allergy. Fourth, 12% of pruritic cats had a food allergy that could be diagnosed by strict diet and provocative challenge. Again, it is very reasonable to offer this trial to owners before allergy testing, although this is not a first-line diagnostic test. If one combines all the flea-responsive cats and the cats in the “other” category that had parasitic diseases, nearly 40% of pruritic cats in this study had a parasitic cause for pruritus. While many clients may claim their cats do not have fleas, many will likely respond nicely to parasiticidal therapy.—Karen Moriello, DVM, DACVD

Source
Clinical characteristics and causes of pruritus in cats: A multicentre study on feline hypersensitivity-associated dermatoses. Hobi S, Linek M, Marignac G, et al. VET DERMATOL 22:406-413, 2011.