Allergy By Numbers

The diagnosis of canine atopic dermatitis is notoriously tricky as you only reach it by ruling out other causes of itching first. The main offenders to strike off the list are infections (bacteria, yeast and/or fungal) and ectoparasites. Of course, just to complicate it further, you may get a combination of these contributing to the pruritus. To make it even more complicated, if you’ve picked them up it then comes down the old chicken and egg scenario; is the infection the cause of the itch or due to it because of an underlying allergy? It’s very easy to see why owners may become confused or get frustrated along the way.

Don’t worry though, help is at hand! Avacta’s Allergy Toolkit packages can help simplify this process by offering complete screening of the common rule-outs (click here for more information). We even provide client friendly information to educate owners as to why ruling out other causes first is so important, and to keep them engaged in the process by seeing the whole diagnostic plan. However, with all that said, there are a few other very simple pointers you can use to help sense check whether allergy should be high up on your list of suspicions.

Several different sets of criteria have been used in recent years to try and define allergy but the most commonly referenced are those by Favrot et al.* in 2010. When 5 out of 8 of these diagnostic criteria are met, the sensitivity and specificity for correctly diagnosing atopic dermatitis is 85% and 79% respectively. Of course, this still leaves a margin of error for misdiagnosis of around 20%, but if you combine this with ruling out ectoparasitic disease and infections, the specificity can be increased considerably.

What are these magical criteria and do they require advanced dermatology skills and knowledge to apply?

  • The short answer is ‘no’. The great thing about them is they are really easy and practical to apply to every single itchy dog.
  • The longer answer, well here’s the criteria set out as a handy bingo card. Remember you only need 5/8 for there to be a statistically, evidence based, high chance of the patient having atopic dermatitis.
Number 1 – The dog is less than 3 years old

Number 2 – The dog lives mainly indoors

Number 3 – The dog is steroid responsive

Number 4 – The dog’s itching started before lesions were seen

Number 5 – The dog’s front feet are affected

Number 6 –The dog’s ear pinnae are affected

Number 7 –The dog’s ear margins AREN’T affected

Number 8 –The dog’s dorso-lumbar area ISN’T affected

What about food allergies?

To be even more helpful, Favrot et al*. also looked at the criteria for food induced atopic dermatitis (FIAD) in the same paper.

Dogs with FIAD (when compared to non-food induced atopic dermatitis dogs) were more likely to:

  • either be very young (< 1 year) or old (> 6 years)
  • experience more gastrointestinal signs

and were less likely to:

  • have seasonal clinical signs
  • have eyelid involvement (although the occurrence of conjunctivitis was similar)
  • be responsive to treatment with glucocorticoids
  • show itching before lesions appeared

What about cats?

If all of those criteria have whet your appetite, you’ll be delighted to know a year later Favrot et al.Ω published a set of feline criteria to help identify cats with non-flea induced allergic dermatitis. See the reference below for details.

Click Here for more information on our Allergy Toolkit. 

For more information about our allergy testing services and our new pruritic dog and cat rule-out packages, please have a look on our website or contact our Technical Services Team on 0800 3 047 047.

Written by Johanna Gourlay– Senior Veterinary Technical Manager

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References:

*Favrot C, Steffan J, Seewald W, Picco F. (2010). A prospective study on the clinical features of chronic canine atopic dermatitis and its diagnosis. Vet Dermatol. 21(1):23-31.

ΩFavrot, C. et al. (2011). Establishment of diagnostic criteria for feline non flea-induced hypersensitivity dermatitis. Veterinary Dermatology, 23, 45–e11