Seasonal Pruritus in a Cat

A 4-year-old neutered male long-haired cat was presented for severe head and neck pruritus of 3-years duration. The pruritus occurred only in the winter.

History

During the summer, the cat, which was from Wisconsin, was normal. However, as the weather became colder and the snow deeper, the cat gradually developed pruritus and hair loss. Clinical signs began in late November and peaked between January and February. The cat lived strictly indoors but had year-round access to a screened-in porch via a cat door. During the summer, the cat was treated monthly with a flea preventative; the last application would occur in October. The owner reported never seeing fleas on the cat, but used flea control because she was concerned about ticks. In the past, glucocorticoids provided relief until the signs resolved with the warm weather. The owner had no other pets. She lived in a rural, wooded area, but there was no local feral cat population due to predation by wildlife.

Examination

Except for the skin, the physical examination was normal. Marked hair loss; erythema; patchy hyperpigmentation; and a papular, crusted eruption were present on the neck and ears. The dorsum of the head was affected to a lesser degree (Figure). The remainder of the cat's skin was normal, as was an otic examination.

Laboratory tests

Skin scrapings were negative for mites, and flea combing was negative for fleas. Wood's lamp examination was negative, and a dermatophyte culture was also eventually found to be negative. Otic cytologic evaluation revealed one to two Malassezia organisms per 40 × field. Impression smears of the skin revealed a predominantly eosinophilic inflammation. CBC revealed leukocytosis (20,000 cells/µl) and marked eosinophilia (14,500 cells/µl).

Ask yourself...

Based on the clinical description and diagnostic testing thus far, what is the optimal initial diagnostic or therapeutic plan for this cat?A. Pursue diagnostic testing for hypereosinophilic syndrome.B. Pursue diagnostic testing for allergies and provide immediate relief from the pruritus with glucocorticoids.C. Treat the cat with itraconazole and/or topical otic glucocorticoids.D. Treat the cat with systemic glucocorticoids.E. Do trial therapy of monthly flea prevention and indoor flea control for 60 to 90 days and offer the client the option of short-term glucocorticoid therapy to relieve pruritus.

Correct Answer E

Do trial therapy of monthly flea prevention and indoor flea control for 60 to 90 days and offer the client the option of short-term glucocorticoid therapy to relieve pruritus.

The most likely cause of the cat's pruritus is flea-allergy dermatitis. This is a recurrent problem with a predictable pattern. Hypereosino-philic syndrome is unlikely-the mean eosinophilia of cats with this syndrome is42 × 103/ml, which is much higher than what was found in this patient. Furthermore, the syndrome is rare; tends to occur in middle-aged female cats; and is associated with such signs of systemic illness as diarrhea, weight loss, vomiting, and anorexia.

Seasonal Atopy?

It is possible that this cat has seasonal feline atopy, especially since the signs respond to glucocorticoids, the illness is seasonal, and the clinical reaction pattern is compatible. Since the signs occur in winter, the most likely allergens would be house dust, house dust mite allergens, and mold allergens. Although the signs can be markedly worse in the winter when the home has less circulation and the furnace is on, these allergens tend to cause year-round signs-this cat's signs are clearly seasonal. Also, it has year-round access to the outdoors via the screened porch.

Food Allergy?

Diagnostic testing for feline atopy would best be pursued after other more likely causes of pruritus are eliminated from the differential diagnosis list and only if the owner is amenable to immunotherapy. Food allergy causes year-round pruritus, and this patient's signs are seasonal; thus, a food trial would not be helpful or cost effective.

Itraconazole and otic glucocorticoids may relieve the signs, but the core issue is what is triggering the recurrent episodes of seasonal pruritus. The same argument can be made for treating the cat with glucocorticoids; it would provide relief but would not provide a long-term solution.

Response to Flea Control

This cat had flea-allergy dermatitis and responded to flea control. For humane relief during the initial treatment period, glucocorticoids were administered. Head and neck pruritus is a common reaction pattern in cats with fleas and/or flea allergy dermatitis. The cat had no signs in the warm months because of flea control measures taken over the summer. The owner would apply the preventative for the last time in October, and clinical signs of flea allergy dermatitis would begin in late November with the waning efficacy of the flea control product. Signs resolved when the owner initiated flea control.

Year-Round Measures

People living in cooler climates commonly discontinue flea control over the winter because the cold weather interrupts the flea life cycle. However, flea control needs to be continued in these regions if the animal's lifestyle puts it at risk for exposure. Live fleas are commonly found on opossums and raccoons in northern climates with severe winters. These animals commonly make winter dens in and around homes during the winter. Large numbers of animals can concentrate in such areas as barns and sheds and under porches. Owners who primarily stay inside when it is cold are often unaware of their presence, and the animals disperse in early spring with the start of the breeding season. In this case, a family of raccoons was removed via live traps from beneath the porch.

Take-Home Messages

• Flea-allergy dermatitis and/or flea infestations are not limited to warm-weather months.• Live fleas are commonly found on raccoons, opposums, skunks, and other small mammals that make their homes in winter near houses.• In climates where fleas are traditionally considered "seasonal problems," the lifestyle of the pet and not the ambient weather should determine whether year- round flea control is needed.• Regardless of geographic region, homeowners should routinely inspect their homes for signs that wild animals are living in and/or near the home.• Appropriately baited (e.g., apples, marshmallows, fish) live traps can be used to remove unwanted wildlife and feral cats.