EVIDENCE-based medicine is a bit of a buzz word (or phrase!) in veterinary circles these days. We’re all encouraged to take a knowledgebased, proof-driven approach to the management of our clinical cases.
With the new RCVS Knowledge charity site now up and running (knowledge.rcvs.org.uk) we have a wealth of information at our fingertips, yet it can still be a struggle to incorporate this into “real life practice”, particularly when under the continual constraints of time pressure that most veterinarians face.
Attending the recent International Society of Feline Medicine’s Annual Congress in beautiful Porto, I sat into two lecture sessions with worldrenowned dermatology specialist and academic, Dr Karen Moriello, to see how she approached the conundrum of the itchy cat from an evidencebased point of view.
Would she be able to tie in the purist annals of dermatological research with the gritty everyday reality of first opinion practice?
Well, after sitting through the twopart presentation Examining the evidence: evidence-based medicine (mostly) and the itchy cat, I can honestly say Dr Moriello is more than familiar with the challenges faced in practice. Along the way, she shared some gems with the audience on real-life practical management of the pruritic feline – as well as the frustrated cat owner!
Here follow some extracts from Dr Moriello’s stepby-step guide to investigating and managing these cases, supported by and in tune with some very convincing evidence.
This protocol has no doubt been honed over years of experience, but it closely resonates with the findings of a large, prospective, multi-centre study by Hobi et al (2011)¹ on the causes of chronic pruritus in cats.
The study involved dermatologists from both Europe and the US, giving it wide applicability: 588 cats were involved in the study, of which 502 went through for final data analysis.
The drop-out of 86 cats highlights that even in controlled expert-led environments, case work-up can be problematic. In this case these 86 cats were excluded from the end results due to unclear or multiple diagnoses being made.
Overall findings were that of the cats in the study:
- 29% responded to flea control
- 25% had non-hypersensitivity causes of pruritus
- 20% had non-food/non-flea hypersensitivity (which was as far as they were able to take the final diagnoses, due to poor compliance of the cats or their owners)
- 12% had food-responsive pruritus
- 15% sabotaged the food trials and were simply undiagnosed
The last point highlights the difficulty in running food exclusion trials with a nocturnal predator. It may be that the rather low incidence of those with foodresponsive pruritus (12%) is in reality a higher figure.
Initial evaluation in the study was standardised and work-up echoed Dr Moriello’s best practice protocol which she calls “dermatological TPR”. (Her full protocol is available through ISFM).
TPR Step 1: rule out parasites and other obvious causes
In the Hobi study 29% of cats responded to a well-designed flea control programme. Those exhibiting inflammatory lesions along with their itching also received antimicrobials. This should be the starting point for investigation of any pruritic cat, and the high number of responders provides strong evidence for this approach.
While all the major skin reaction patterns were seen within this group, miliary dermatitis was seen most commonly. This might not be particularly surprising, but it’s interesting to note that this was the first largescale study to document flea allergic dermatitis as the most common cause of pruritus in cats!
Next up, given the evidence along with the potential to “cure” or effectively manage responders, other parasitic causes should be investigated, even though you may be hankering to go down the suspected “hypersensitivity” route at this stage.
Investigative techniques include skin scrapings, faecal exams and response to therapy trials (e.g. ear mite treatment, lime sulphur washes). In the study, offenders such as Cheyletiella, Demodex (especially D. gatoi) and mites such as Otodectes and Notoedres, as well as ticks, were all found, bringing the grand “parasitic total” – including fleas – to 39%. That’s a whopping near-40% of itchy cats controlled just by ectoparasitic treatment. Well worth doing.
Step 2: rule out D. gatoi
This little critter merits a dedicated step. It’s a major differential for cats with symmetrical alopecia and “bald belly syndrome”. Demodex gatoi leads to intense pruritus, and while diagnosis can be made through hair trichograms, skin scrapings or faecal flotations, in many cases treatment trials are required.
Lime sulphur treatment, ivermectin, moxidectin/imidacloprid spot-on and fipronil spray are all options (some off-label). Flea control should be continued during this period, even if initial treatment wasn’t successful; this is because an unexpected flea infestation could confound the workup.
Step 3: rule out pruritic microbial overgrowth (this step might precede step 2 if more practical to do at that point)
If you haven’t started antimicrobial therapy already in step 1, this is now done, using a response-to-treatment trial.
Microbial overgrowth is increasingly recognised in cats. Key presentations to look out for are excessive scaling, with the scales pierced by hairs or eosinophilic lesions. Some lesions, though, can be very subtle and hard to spot. A strong white light for examinations is useful as often normal consulting room light isn’t bright enough.
In a study by Wildermuth (2011)² treatment with a potentiated amoxicillin led to a 96% reduction in size of eosinophilic plaques, and 43% reduction in size of lip ulcers (note though that any lip trauma will result in an ulcer in a cat, so make sure you investigate for mouth trauma at the same time!).
Topical antimicrobial treatment can be used – chlorhexidine sprays and mousses are now available which are cat-friendly to comb through the coat. Antibacterial/antifungal shampoos, accelerated hydrogen peroxide shampoo or rinse can also be used, and focal treatment of lesions is possible in some cases. Systemic treatments include 21 to 30 days of broadspectrum antibiotic or an agent based on culture.
Parenteral or oral glucocorticoid should not be used during this time. A 30-day course of oral itraconazole can be used for yeast overgrowth; cats do not tolerate ketoconazole and so it should be avoided.
Step 4: rule out food intolerance
Not a first investigative step, but one that you should take before referral. Dr Moriello noted that owners are not happy when they are referred to a dermatologist only to come home with a bag of food!
If the pet owner refuses to do a diet trial, make sure you note it in your clinical records. Keep up the flea control throughout this time.
In the Hobi study, 12% of cats were diagnosed with a food allergy. While this was found to be the least common cause of pruritus in this study, it’s worth remembering quite a number of cats were excluded from the final study results because of non-compliance.
Differentiating skin lesions aren’t helpful in the diagnosis of food allergy; digestive signs though may give some pointers, and were more common in the Hobi study (frequent or soft stools).
Interestingly, while head and neck lesions were found to be more common in the food allergy group, the finding of otitis externa was more commonly associated with the nonflea, non-food hypersensitivity cases.
Dr Moriello said there was no consensus on the best diet to use for a food trial, but hydrolysed diets did seem to be increasingly used. Shopbought over-the-counter “novel protein diets” are not suitable, due to the likelihood of contamination with other ingredients.
Another point to note was that the oft-quoted food trial length of 12 weeks was originally extrapolated from retrospective data on dogs, and from just one study (Rosser, 1993³); 75% of the cases in the study responded within six weeks and so Dr Moriello felt that six to eight weeks of an exclusion trial is sufficient. Oh, and continue with the flea control!
Step 5: manage the nonflea/non-food/non-“other” cat
In the Hobi study, this clinical grouping accounted for 20% of the cats and was categorised as “feline atopic dermatitis”. These diagnoses were made after going through the aforementioned steps and ruling out similar appearing conditions, food allergy and fleas, as well as exhibiting a positive response to type 1 antihistamines, glucocorticoids or cyclosporine.
All four reaction patterns (miliary dermatitis, erosions or ulcerations, symmetrical alopecia and eosinophilic granuloma complex) were seen in this group, but the latter two found most commonly.
So it’s finally at this point in the plan, while continuing with flea control, that Dr Moriello advocates any discussion of allergy testing and immunotherapy, antipruritic therapy or cyclosporine use. Note that IgE is not useful for screening for confirming allergy. It’s best to use this test at the end when you know what you’re dealing with.
There aren’t many published studies of atopic dermatitis in large groups of cats (though Ravens et al, 20144 is worth a look), and antihistamines are not always highlighted as being particularly useful, but she points out that often the pets that find their way into studies are often the ones that don’t do well in the first place.
References
1. Hobi, S., Linek, M., Marignac, G. et al (2011) Clinical characteristics and causes of pruritus in cats: a multicentre study on feline hypersensitivity associated dermatoses. Vet Dermatol 22: 406-413.
2. Wildermuth, B. E. et al (2012) Response of feline eosinophilic plaques and lip ulcers to amoxicillin trihydrate-clavulanate potassium therapy: a randomized, double-blind placebo-controlled prospective study. Vet Dermatol. 23 (2): 110-8, e24-5. doi: 10.1111/j.1365-3164.2011.01020.x. Epub 2011 Dec 1.
3. Rosser, E. J. Jr. (1993) Diagnosis of food allergy in dogs. J Am Vet Med Assoc. 203 (2): 259-262.
4. Ravens, P. A. et al (2014) Feline atopic dermatitis: a retrospective study of 45 cases (2001-2012). Vet Dermatol. 25 (2): 95-102, e27-8. doi: 10.1111/vde.12109. Epub 2014 Mar 5.
