Diagnostic testing
The results of a flea combing were negative for fleas and Cheyletiella species mites. The results of a complete blood count were normal. Impression smears of the lesions on the forelimb revealed
neutrophils with intracellular cocci and eosinophils, and impression smears of the ventral abdomen revealed large numbers
of shed keratinocytes but no infectious agents. A dermatophyte culture revealed no pathogen growth 21 days later. The owner
declined skin scrapings because the results of numerous previous skin scrapings had been negative. Negative results from a
skin scraping do not rule out feline demodicosis because demodectic mites can be difficult to find.
Histologic examination of skin biopsy samples obtained from the lesion on the forelimb and the ventral abdomen revealed perivascular
eosinophilic dermatosis. Special stains did not reveal any pathogens. These findings were suggestive of an allergic skin disease.
A urine sample obtained by cystocentesis for analysis and culture yielded Escherichia coli that was sensitive to all antibiotics tested.
Diagnosis and treatment
The working diagnosis was E. coli bacterial cystitis and allergic dermatitis (atopy or food allergy) with a secondary bacterial infection. Fourteen days of
cephalexin therapy (30 mg/kg orally b.i.d.) resolved the cat's urinary tract infection (based on a negative urine culture
result and resolution of clinical signs) and forelimb lesions. The cat's inappropriate urination also resolved. The cat's
over-grooming decreased but did not completely resolve. Excessive licking of the abdomen has anecdotally been associated with
cystitis. But if cystitis had caused the over-grooming, then the over-grooming should have resolved with the successful antibiotic
therapy. The lack of complete response to antibiotic therapy indicated that an underlying pruritic trigger was still present.
Table 1 : In Vitro Allergy Test Results*
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Because the cat was receiving a flea preventive routinely and had negative flea combing results, food allergy and feline atopy
were the top differential diagnoses. So an elimination diet trial was initiated, and all the cats were fed a novel protein
diet (Prescription Diet Feline z/d—Hill's Pet Nutrition) for eight weeks. During the first six weeks of the food trial, the
affected cat received oral fexofenadine hydrochloride (Allegra—Aventis; 2 mg/kg b.i.d.). The cat stopped licking while receiving
this antihistamine; however, when the drug was discontinued during the last two weeks of the food trial, the licking returned,
and signs of alopecia were beginning to recur.
Figure 3 : The cat's abdomen two years after immunotherapy treatment.
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Serum was submitted for an in vitro allergy test with various weeds, trees, grasses, fungi, and environmental elements as
possible allergens. Only the environmental allergens scored above 150 and were considered abnormal (Table 1). Feline atopy was diagnosed. The cat was successfully treated with immunotherapy for house dust mite allergy; its over-grooming
and self-mutilation ceased (Figure 3). The benefits from immunotherapy were evident by six months of treatment. In some cases, it can take up to 12 months for
a complete response to immunotherapy. The cat also required fexofenadine twice a year for one to three weeks to treat pruritic
outbreaks.
Discussion
One of the most frustrating problems in feline dermatology is determining whether a cat presented for evaluation of self-mutilation
and over-grooming has a behavior problem or a true dermatologic problem.1-3 This case was seen as a second opinion, and it was useful to know that previous behavior therapies, including pheromone and
paroxetine therapy, had not worked. It has been my experience that pheromone therapy is often useful in homes in which cats
are aggressive, particularly if the pheromone is sprayed in the home before the new cat is added. Paroxetine, a specific serotonin
reuptake inhibitor, has been helpful in cases of feline aggression, over-grooming, and inappropriate urination, in my experience.
But in this case, the drug was ineffective in treating both the over-grooming and the inappropriate urination. This information
was helpful in convincing the owner that the cat's problem was likely pruritic and not behavioral. It is interesting that
the cat had not received glucocorticoids before referral. Glucocorticoid responsiveness is often held as the big clue that
a skin disease is pruritic and probably caused by allergies. The problem is that while glucocorticoids are antipruritic, they
can also be mood-modifying, most noticeably in cats. A response to glucocorticoids in a cat with symmetrical alopecia does
not always indicate a pruritic cause.
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