Today's Veterinary Practice

JAN-FEB 2018

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45 JANUARY/FEBRUARY 2018 ‚óŹ TVPJOURNAL.COM CONTINUING EDUCATION Exclusion of Other Diseases Regardless of the history and criteria, CAD should never be diagnosed until diseases that resemble it, such as flea allergy dermatitis, ectoparasitic disease (eg, sarcoptic mange, cheyletiellosis, pediculosis, trombiculiasis, and otoacariasis), and primary skin infections have been ruled out. The initial steps of a basic workup to rule out ectoparasites are flea combing, skin scraping, hair plucking, and cytologic examination of skin and ear samples. Skin lesions and pruritus associated with flea allergy dermatitis are most common at the lumbosacral area, tail base, and caudomedial thighs, 6 which are not commonly affected areas in CAD. Patients with CAD exhibit frequent, sometimes recurrent, staphylococcal and yeast skin infections, which can exacerbate pruritus and dermatitis; 6 therefore, patients predisposed to secondary skin infection should be considered and screened for CAD. Skin biopsy results are usually nonspecific and inadequate for diagnosing CAD. 6 However, in some cases, skin biopsy may be indicated to rule out a diagnostic differential, such as cutaneous lymphoma ( FIGURE 6 ). 6 Cutaneous epitheliotrophic T-cell lymphoma may present with pruritus, excessive scales, and generalized erythema in dogs and may mimic atopic dermatitis lesions. 8 Intradermal and IgE Testing Allergy testing, which includes serologic evaluation of allergen-specific IgE and intradermal skin testing, should not be used for the diagnosis of CAD. 6 Many healthy dogs are sensitized to environmental allergens and consequently have positive test results. Furthermore, many dogs with clinical signs of CAD have negative results on these tests; the term atopic- like dermatitis describes this group of dogs. 1,9 Allergy testing should be carried out only to identify allergens to be used for allergen-specific immunotherapy and desensitization (see Allergen Immunotherapy). UPDATES ON TREATMENT CAD is a multifactorial chronic disease that requires a multimodal treatment approach to decrease pruritus and inflammation below the threshold of clinical signs. Guidelines from the International Task Force on Canine Atopic Dermatitis 1,3 recommend therapeutic interventions based on identifying and managing the flare factors ( FIGURE 3 ), as well as whether the patient is experiencing an acute flare or has chronic skin lesions. A rational approach to treatment is required; the keys to success are client education and a combination of interventional measures specific for flare factors and symptomatic treatment. The management of each patient starts with: 1. Identifying and addressing (or, if possible, avoiding) the associated flare factors ( FIGURE 4 ) 2. Using a topical and/or systemic treatment to decrease inflammation and pruritus Management of Flare Factors Specific avoidance interventions depend on identification of all the factors associated with a flare for clinical signs in an individual dog. Common flare factors include fleas and fleabite hypersensitivity, bacterial or yeast overgrowth, and food and environmental allergens. CAD due to food and environmental allergens can present with identical clinical signs and may, in fact, be a concurrent problem. Fleas and Fleabite Hypersensitivity Dogs with CAD are predisposed to fleabite hypersensitivity if exposed repeatedly to flea salivary antigens. 10 As a result, all dogs with CAD should be protected with year-round flea adulticides combined with relevant environmental measures. Some dogs may present with concurrent clinical signs of CAD (eg, licking feet, ear infections) and fleabite hypersensitivity (eg, pruritus and hot spots in tail base area); these patients need aggressive flea treatment as well as environmental measures. 1 Bacterial or Yeast Overgrowth Specific antibacterial/antifungal interventions should be based on regular cytologic evaluation (impression smears, tape) of atopic skin lesions and documented presence of bacteria/yeast at these sites. Because atopic patients frequently develop recurrent ear and skin infections with Staphylococcus and Malassezia species ( FIGURE 5 ), topical once- to twice-weekly therapy using antimicrobial shampoos (eg, chlorhexidine, benzoyl peroxide, miconazole, ketoconazole) and ear cleansers are recommended as an essential component in the long-term management of secondary infected CAD. The widespread emergence of multidrug-resistant

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