21 Feline symmetrical alopecia
Symmetrical alopecia is a common presentation in the cat. Historically, the alopecia was thought to be due to an endocrinopathy because of the lack of any apparent inflammation in many cases. It is now known that the majority of cases of symmetrical alopecia are due to pruritus. There are many causes for symmetrical alopecia, including parasitic and allergic disease, and a thorough and systematic investigation is indicated in recurrent disease to try to identify and correct the underlying cause.
As in all dermatology cases, a thorough history (see Chapter 1) is essential in making an accurate diagnosis. Frequently, in cases of symmetrical alopecia, the client may be unaware that the cat is actually overgrooming.
Feline symmetrical alopecia usually presents as non-inflammatory hair loss, although there may be evidence of focal excoriations. The most frequently affected areas include the neck, forelimbs, groin and flanks.
There are four main categories of disease that result in pruritus in cats: parasites; infections; hypersensitivity disorders; and a diverse fourth group which includes some infectious, autoimmune, metabolic and neoplastic diseases amongst others. When drawing up a list of differential diagnoses with a view to further investigation, it is important to initially rule out/treat parasitic infestations before considering the infectious and allergic causes of pruritus. Pruritus is often multifactorial and a methodical approach, following a series of sequential diagnostic rule-outs, will maximize the chances of making a diagnosis and instituting successful treatment and management.
In this case, there was a history of flea exposure, but thorough flea control had been instituted with no improvement, so flea allergy dermatitis, as a sole cause of the pruritus, was unlikely. Nevertheless, flea allergy dermatitis could still be involved and thorough flea control would need to be maintained. A limited antigen diet trial had been tried, but only for 4 weeks, and this is too short a period to be able to thoroughly exclude a cutaneous adverse food reaction. Ideally, a diet trial should be continued for a minimum of 6 weeks and on occasion for as long as 3 months. There was no history of an anxiety-inducing situation, but psychogenic alopecia should be considered where there is symmetrical alopecia.
The first stage in the investigation of feline pruritus, whatever the presentation, is to rule out the involvement of ectoparasitism, particularly fleas. Visual examination for evidence of flea infestation, and microscopic examination of scale and skin scrapes for the detection of ectoparasites, are insensitive methods and thorough treatment of the patient, all in-contact animals and the household (and possibly car) environments is always indicated in these cases. If there has been no response to thorough ectoparasitic therapy, a diet trial and possibly intradermal and/or an ELISA environmental panel are indicated. Thus, the following further investigations were conducted:
Trial ectoparasitic treatment: Good flea control was already in place, but in order to be confident about ruling out the involvement of cheyletiellosis, all animals were treated with fortnightly applications of selamectin for a period of 4 weeks. There was no response to this and the cat continued to overgroom. Monthly applications of fipronil were continued after the trial selamectin therapy.
Diet trial: An extended, 10-week, restricted antigen diet trial was conducted, feeding a proprietary capelin and tapioca food. To give relief from pruritus, for the first 4 weeks of the trial the patient was treated with prednisolone (10 mg s.i.d. for 1 week then 5 mg s.i.d. for 1 week then 5 mg every other day). Re-examination after 4 weeks showed a marked improvement, with resolution of overgrooming and some hair regrowth over affected areas, but marked polyphagia had been evident and the cat had gained weight. After a further 6 weeks, there was recrudescence of overgrooming and alopecia.
Intradermal testing: An intradermal test was performed on completion of the diet trial, which gave positive reactions to the house dust mite Dermatophagoides farinae, the storage mites Acarus siro and Tyrophagus putrescentiae, as well as sheep epithelia, mixed feathers, couch grass, orchard grass, lambs quarter and alder.
Note that intradermal and serological allergy testing are less reliable and can be harder to interpret in the cat compared to the dog; nevertheless, some cats will produce strong positive reactions to one or both tests. The main reason to conduct these tests is for selection of allergens for immunotherapy.