Page 158 - WSAVA2018
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 25-28 September, 2018 | Singapore
Age of onset:
The typical age of onset is reported to be adult dogs of 6 months and older, although it has been diagnosed in dogs as young as 2 months of age.
Contact allergies typically affect the sparsely haired regions of the face (muzzle and periocular region) concave pinnae, inguinal area, feet, perineal and genital area (plants or carpets) and scrotum (floor detergents, cement, bleach).
Lesions are particularly evident on glabrous areas. Intense pruritus is common and in severe cases can lead to a lack of response to anti-inflammatory dosages of corticosteroids. A primary erythemic maculopapular eruption is visible in affected areas. Self trauma and chronic inflammation may lead to hyperpigmentation and lichenification.
Scratch or patch test
A scratch/patch test can then be performed to identify specifically what the trigger is. A patch pf skin is clipped over the lateral thorax. The test sites are then outlined with a marker pen. The suspected surfaces are then rubbed onto the skin. A scratch to the skin surface can be made using a 23G needle to ensure penetration of the stratum corneum.
Topical medications and shampoos can be applied in their normal formulations, powders can be mixed with petroleum jelly and floor cleaners and disinfectants
can be applied at their normal working oilutions. Plant extracts can be made using a mortar and pestle. The sites are then monitored for signs of erythema, oedema and pruritus. The test should be read at 15 to 20 minutes looking for immediate reaction while the substance is still on the skin. The test solution is not washed off. Owners should be asked only to gently wash or wipe the dried solution off with tap water after 24 hours and then to observe the test site for redness or rash over the next 24 to 48 hours.
Immunotherapy is not effective. The best approach
is avoidance. When avoidance is not feasible, glucocorticoids can be used either topically or systemically to minimise the severity of clinical signs. Pentoxifylline has been reported to be effective for contact allergies but works best as a preventative rather than treatment and should be started 48 hours prior to exposure.
Griffin C. Diagnosis of canine atopic dermatitis. In: Veterinary Allergy. 2014 Eds Noli, Foster and Rosenkrantz. John Wiley and sons. p70-77.
Favrot C, Steffan J, Seewald W et al. A prospective study on the clinical features of chronic canine atopic dermatitis and its diagnosis. Vet Dermatology. 2010 21: 23.31.
Marsella R. Contact allergy. In: Veterinary Allergy. 2014 Eds Noli, Foster and Rosenkrantz. John Wiley and sons. p185-190
Picco F, Zini E, Nett C et al. A prospective study on canine atopic dermatitis and food induced allergic dermatitis in Switzerland. Vet Dermatology. 2008; 19: 150- 155
The diagnosis of contact allergy is usually based on the combination of clinical signs and response to confinement followed up by scratch or patch testing. Interpretation may be complicated by the fact that animals may have more than one condition at the same time, some of which wax and wane. An integrated and sequential investigation is usually required if successful results are to be achieved.
Four diagnostic tests can be used to investigate suspected contact dermatitis
1. Removal of suspected causes of contact irrita- tion: collar, plastic food bowl, topical medication, shampoo or floor disinfectant.
2. Environmental restriction: bath and isolate dog in a new environment (kennel or hospitalisation) for allergen avoidance. Complete resolution of the lesions within 7 to 10 days following restric- tion suggests that contact dermatitis may be involved; re-challenge to confirm the diagnosis and lesions should recur within 1 to 4 days.
3. Scratch or patch testing: permits identification of the allergen (kikuyu grass, buffalo grass, Trad- escantia sp etc) and is usually performed after confinement.

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