Today's Veterinary Practice

JAN-FEB 2018

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PEER REVIEWED 44 CE: CANINE ATOPIC DERMATITIS PATHOGENESIS The pathogenesis of CAD is complex. Percutaneous sensitization to environmental allergens (eg, dust mites, pollen, mold) and/or allergens from food induces skin infiltration by various inflammatory cells, activation of resident cells, and local production of inflammatory/itch mediators. 1,2 Several factors can exacerbate CAD ( FIGURE 3 ), 1-3 such as: ■ Ectoparasites, particularly fleas ■ Environmental factors (eg, increase in seasonal allergen) ■ Cutaneous colonization/infection by bacteria (Staphylococcus pseudintermedius) and yeast (Malassezia pachydermatis) ■ Epidermal barrier dysfunction UPDATE ON DIAGNOSIS Despite significant efforts to identify a "diagnostic test" for CAD, the diagnosis remains clinical. It is based on the following: ■ History ( BOX 1 ) 4,5 ■ Characteristic clinical criteria ( BOX 2 ) ■ Exclusion of other diseases with a similar clinical presentation 1,3,6 Clinical Criteria Recently, a new set of criteria for CAD diagnosis, known as Favrot's criteria ( BOX 2 ), has been implemented to help veterinarians interpret clinical findings when confronted with an itchy dog. 7 These criteria were developed from a large case series of confirmed cases of CAD. Complex statistical analysis was used to identify a set of clinical features that had maximum association with CAD. However, these criteria have a sensitivity and specificity of about 80% when 5 of 8 are fulfilled. This means that using them as the sole "diagnostic test" would lead to a wrong diagnosis in every fifth dog. 1,7 Therefore, they should be applied concurrently with a careful workup for exclusion of diagnostic differentials, such as ectoparasitic diseases and skin infections. When they are used in this way, the specificity of diagnosis can be expected to increase markedly. FIGURE 3. Flare factors involved in pathogenesis of CAD. CAD Mites Pollens Molds Foods Fleas Bacteria Yeast BOX 1 Important Details in History of Dogs Suspected of Having CAD Age at onset Seasonality of clinical signs Pruritus with no skin changes (pruritus sine materia) at onset Familial or breed predisposition (eg, West Highland white terrier, Golden or Labrador retriever, German shepherd, Boxer, French bulldog, bull terrier, shar-pei) 3,4 Previous response to glucocorticoids BOX 2 Favrot's Criteria 1. Onset of signs under 3 years of age 2. Dog living mostly indoors 3. Glucocorticoid-responsive pruritus 4. Pruritus sine materia at onset (ie, alesional pruritus) 5. Affected front feet 6. Affected ear pinnae 7. Nonaffected ear margins 8. Nonaffected dorsolumbar area

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