In this case, a urinary tract infection caused the inappropriate urination. Simple diagnostic tests (flea control, skin scrapings,
flea combings, lack of evidence of contagion) rapidly ruled out parasitic causes of pruritus. A dermatophyte culture was indicated
even though other cats were unaffected. Dermatophytosis can present with a wide range of clinical signs and mimic many diseases,
so a dermatophyte culture is always cost-effective, especially when more expensive diagnostic tests (e.g. food trials, allergy testing, skin biopsy) are being considered. Rarely is blood work helpful in diagnosing routine skin
diseases; however, in cats with flea allergy dermatitis, elevated eosinophil counts may signal a flea or parasite infestation.
One investigator found that flea allergy dermatitis was most common in cats with symmetrical alopecia and an elevated eosinophil
count.4 Keep in mind that this test is not valid if the cat has recently received glucocorticoids. Skin biopsy was performed in this
cat primarily to look for eosinophils in the skin; their presence was helpful in building a case for allergic skin disease.
However, a lack of an eosinophilic dermatitis does not eliminate allergies as a cause of over-grooming.
In this case, the cat's over-grooming was caused by year-round pruritus, and the most likely trigger was an allergic reaction
to house dust mites. By their nature, cats tend to rest and relax in areas often heavily contaminated with dust (e.g. under beds, in closets). The cat responded well to immunotherapy; in addition, a marked increase in pruritus was noted when
the immunotherapy was discontinued. The cat was asymptomatic in its first home probably because the cat was less than 1 year
of age and the home was heated by radiant heat. In the second home, the cat was a little older and the home had forced air
heat. It has been my experience that animals with house dust mite allergies are more symptomatic in homes with forced air
heat than in those heated by radiant heat. Furthermore, the cat required short-term fexofenadine to treat pruritic outbreaks.
These episodes occurred during the first week that the air conditioning or heat was used. Dust and debris collect in the air
return vents when they are not used and are blown into the house when the heat or air conditioning is first turned on. It
is possible that this dust and debris contain high concentrations of house dust mites.
1. Scott DW, Miller WH, Griffin CE. Muller and Kirk's small animal dermatology. 6th ed. Philadelphia, Pa: WB Saunders, 2001.
2. Mueller RS, Jackson H. Atopy and adverse food reaction. In: Foster A, Foil C, eds. BSAVA manual of small animal dermatology. 2nd ed. Gloucester, England: British Small Animal Veterinary Association, 2003;125-136.
3. Roosje P, Henfrey J. An approach to alopecia in the cat. In: Foster A, Foil C, eds. BSAVA manual of small animal dermatology. 2nd ed. Gloucester, England: British Small Animal Veterinary Association, 2003;71-76.
4. Thoday KL. Aspects of feline symmetrical alopecia. In: von Tscharner C, Halliwell REW, eds. Advances in veterinary dermatology. Vol 1. London, England: Baillière Tindall, 1990;47-69.
The photographs and information for this case were provided by Karen A. Moriello, DVM, DACVD, Department of Medical Sciences,
School of Veterinary Medicine, University of Wisconsin, Madison, WI 53706.