SKIN PROBLEMS ARE SUGGESTED TO BE THE MOST COMMONLY ENCOUNTERED COMPLAINT in first opinion small animal practice1 but are a frequent source of frustration for vets and owners.
The issue is that many owners expect a quick fix. The “pattern recognition” approach, so often appropriately and successfully applied to other common presentations, is likely to fail when it comes to dermatology. A presumptive diagnosis and test treatment may satisfy the owner’s expectation in the short term but, over time, symptoms will probably return more and more frequently and the owner will become dissatisfied.
So while the itchy dog or cat might be a routine and seemingly straightforward consultation, a problem-based approach is almost always going to be necessary to achieve success, and a lengthy, thorough workup is actually most likely to deliver the “quickest fix”.
The reason for this is firstly that the majority of skin problems look the same symptomatically and we cannot rely on pathognomonic signs.2,3,4 Nowhere is this more evident than in the examination of chronic atopic dermatitis (CAD) and cutaneous adverse food reactions (CAFR).
Multifactorial condition
CAD appears to be a multifactorial condition5,6 thought to be closely linked to a dysfunction in the skin’s barrier role.7,8 While it is generally characterised by pruritus and a syndrome of typical findings, clinical presentation can be highly variable.
In dogs, symptoms may include otitis externa, conjunctivitis, pododermatitis and pyoderma4 and in cats we may see military dermatitis, eosinophilic granuloma complex and bilaterally symmetrical alopecia.10, 11
Adverse food reactions encompass disorders with an immunological basis (food allergy or dietary hypersensitivity), non-immunologic reactions (food intolerance) and toxic reactions (food intoxications). Intoxications are a common problem, particularly in dogs, but are more likely to cause gastrointestinal symptoms.
However, CAFRs, defined as a repeatable cutaneous reaction to an otherwise harmless component of the food, are an important differential in cases of chronic pruritus and include both hypersensitivity and intolerance.
Although an IgE-based Type 1 Hypersensitivity reaction has been characterised in some dogs with CAFR, the majority of cases do not seem to have an immunological basis12 and it is impossible to distinguish the type of food reaction from the symptoms seen. In fact, clinical presentation of CAFR tends to mimic atopic dermatitis.9, 10
So CAD and CAFR may both manifest in a variable presentation of clinical signs and are indistinguishable at first sight. Furthermore, there seems to be overlap between the two conditions. CAD and CAFR may be present at the same time3,4 and it is possible that canine CAD may be induced by CAFR.12,13 The situation is particularly confused in cats, in which atopic dermatitis is less well characterised and it has been suggested that CAFR may be more common than CAD.10
All of this means that a presumptive diagnosis is near impossible, but does that matter? We could opt to test treat for the most common problems and see if that improves the situation, but the problem here is that secondary bacterial and yeast infections are so very common.
In the unlikely event that they are not already a complicating factor at first presentation, failure to properly address the underlying cause of the skin problem will likely lead, fairly soon, to the development of these complications, leaving us fire-fighting the symptoms.
More likely, a secondary pyoderma has already developed, meaning that a test treatment with antibiotics and anti-pruritic medication will bring miraculous results, reinforcing the owner’s expectation of a quick fix, but only as a temporary reprieve. The symptoms will recur, as will the owner’s frustration. In fact, long-term treatment with anti-inflammatory or anti-pruritic therapeutics is only likely to fail in cases of CAFR.14
Additionally, in this age of concern over antibiotic resistance, it is more important than ever that we are systematic in our approach to diagnosis and management, and understand what we are trying to achieve with medication. Once we have identified the underlying cause or causes for our patient’s symptoms, we can choose to use the right therapeutics appropriately.
A thorough, problem-based approach is the right one for these cases. By systematically eliminating – or identifying and treating – each potential cause in turn, and assessing the patient’s response at every stage, we can achieve a specific diagnosis.
Allergy testing may have a role to play in this approach, depending on the individual case, but only as part of this stepwise diagnostic pathway. If we have reached the stage that atopic dermatitis is the likely diagnosis and other causes have been eliminated, serum or intradermal testing can be useful as a confirmation and to help identify the allergens involved, but these should not be relied upon as screening tests.4
Likewise, blood testing for “food allergy” can seem tempting as a rapid diagnostic tool but, at most, should be reserved to help identify possible problem dietary allergens to avoid. Given that not all CAFRs are immunological in origin, and the immunological processes have not been well characterised in those that are, IgE blood testing is not a reliable diagnostic tool.9
While it is a prolonged process, an exclusion diet trial will likely be an essential part of the diagnostic approach. Once ectoparasite-induced allergies and microbial infections have been ruled out, an eight to 12- week diet trial – ideally followed by challenge with the original diet – will be necessary to confirm or rule out a dietary basis to the symptoms.
Diet developments
There are now a wide range of complete and balanced hydrolysed protein diets available for both dogs and cats, with more recent developments in this area bringing us diets for both species based on proteins hydrolysed to the level of single amino acids or chains of a few peptides.
Whatever the diet used, however, owner compliance is essential to success, so a detailed conversation to explain the aims and reasoning for this approach will be necessary. This applies to the whole diagnostic process. By recognising our clients’ expectations for that elusive quick fix and explaining why this is not realistic, we can bring them on the diagnostic journey with us.
We can explain the importance of a specific diagnosis and that, once we know what is behind their pet’s frustrating symptoms, we have a very good chance of successfully controlling them through management, appropriate medication and the right diet for the individual patient’s needs.
References
1. Robinson, N. J., Dean, R. S., Cobb, M. et al (2015) Investigating common clinical presentations in first opinion small animal consultations using direct observation. Veterinary Record 176: 463.
2. Favrot, C. (2013) Feline non-flea induced hypersensitivity dermatitis – Clinical features, diagnosis and treatment. Journal of Feline Medicine and Surgery 15: 778-784.
3. Verlinden, A., Hesta, M., Millet, S. et al (2006) Food Allergy in Dogs and Cats: A Review. Critical Reviews in Food Science and Nutrition 46 (3): 259-273.
4. DeBoer, D. J. and Hillier, A. (2001) The ACVD Task Force on canine atopic dermatitis (XV): fundamental concepts in clinical diagnosis. Veterinary Immunology and Pathology 81: 271-276.
5. Olivry, T. and Saridomichelakis, M. (2016) An update on the treatment of canine atopic dermatitis. The Veterinary Journal 207: 29-37.
6. Nuttall, T. (2008). Management of atopic dermatitis. Veterinary Focus 18 (1): 32-39.
7. Marsella, R., Olivry, T. and Carlotti D. N. International Task Force on Canine Atopic Dermatitis (2011). Current evidence of skin barrier dysfunction in human and canine atopic dermatitis. Veterinary Dermatology 22 (3): 239-248.
8. Olivry, T. (2011). Is the skin barrier abnormal in dogs with atopic dermatitis? Vet Immunol Immunopathol 144 (1-2): 11-16.
9. Plant, J. (2011) Cutaneous adverse food reactions in dogs. Veterinary Focus 21 (3): 18-23.
10. 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. Veterinary Dermatology 22: 406-413.
11. Wolberg, A. and Blanco, A. (2008) Pruritus in the cat. Veterinary Focus 18 (1): 4-11.
12. Hillier, A. and Griffin, C. (2001) The ACVD task force on canine atopic dermatitis (X): is there a relationship between canine atopic dermatitis and cutaneous adverse food reactions? Veterinary Immunology and Immunopathology 81: 227-231.
13. Olivry, T., DeBoer, D. J., Favrot, C. et al (2010) Treatment of canine atopic dermatitis: 2010 clinical practice guidelines from the International Task Force on Canine Atopic Dermatitis. Veterinary Dermatology 21 (3): 233-248.
14. Hill, P. B., Lo, A., Eden, C. A. N. et al (2006) Survey of the prevalence, diagnosis and treatment of dermatological conditions in small animals in general practice. Veterinary Record 158: 533-539.
