Atopic Dermatitis: The New Paradigm and How it Changes the Way We Treat It

The understanding of canine atopic dermatitis (cAD) has changed dramatically over the last several years. This has lead to a change in our therapies. It is now accepted that the pathogenesis of cAD involves not only an immunologic component but also a barrier dysfunction. This disruption of normal barrier function leads to increased allergen penetration and sensitization. Thus, the therapeutic approach has changed from addressing only the immunologic abnormality (hypersensitivity) to one that also includes managing the barrier dysfunction. It is essential that before treatment for cAD is begun that the proper diagnosis has been established. It is recognized that the diagnosis of cAD is a clinical diagnosis made by ruling out other pruritic diseases1. Criteria that can help establish a diagnosis of cAD are2 1. Onset of signs under 3 years of age 2. Dog living mostly indoors 3. Glucocorticoid-responsive pruritus 4. Pruritus sine materia at onset (i.e. alesional pruritus) 5. Affected front feet 6. Affected ear pinnae 7. Nonaffected ear margins 8. Nonaffected dorso-lumbar area If the dog meets 5 criteriathere is a specificity of 79% (21% false positives) and a sensitivity of 85% (15% false negative) If the dog meets 6 criteriathere is a specificity of 89% (11% false positives) but the sensitivity decreases (more false negative) to 58% (42% false negative) In the author’s experience an easier and very accurate modification can be used as follows. It is called the “One minute atopic dermatitis test”. If you have a pruritic dogyou can be fairly certain that he/she has cAD ectoparastites and infection (bacterial, yeast/fungal) have been ruled out. There are exceptions to the rule but they are very uncommon and suspicion for these diseases would be raised based on signalment, history and physical findings. Note that serum testing/intradermal testing and/or food trials may be needed to ID flare factors of cAD but are not used to diagnose cAD. Whether these additional tests are necessary depends on the severity of the cAD