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the cause of the clinical signs of dogs with pruritus. Allergy testing is not considered to be a major tool in the diagnosis.
KEY POINTS FOR THE DIAGNOSIS OF ATOPIC DERMATITIS
  Pruritus must be present. Early in the disease some CAD dogs exhibit pruritus with no evidence of any skin lesions. Other cases may have erythema of the affected areas but no other lesions. In some dogs the initial presentation of CAD is an episode of otitis externa.
In the first stages of the disease, pruritus generally responds well to corticosteroid therapy (0.3mg to 0.5mg/ kg prednisolone daily).
CAD is a progressive disease. Most of the clinical signs develop due to self trauma and/or secondary infections. Chronic changes of CAD include alopecia, excoriations, hyperpigmentation, lichenification and/or signs of secondary bacterial (papules, pustules, crusts, erosions, epidermal collarettes) and/or yeast (hyperpigmentation, lichenification) infections. Recurrent ear infections are frequently observed. It is important to recognise these because they may require specific management in addition to control of the allergic dermatitis.
Other historical features help to support the diagnosis of CAD such as sneezing, reverse sneezing and conjunctivitis. A lack of gastrointestinal signs in a
dog with pruritus compatible with ACD also helps by decreasing but not eliminating food as a cause.
DIAGNOSIS
The diagnosis of canine atopic dermatitis is based
on typical history and clinical presentation and most importantly by exclusion of other pruritic skin diseases.
Pruritus the defining feature of canine atopic dermatitis is a common presenting problem for veterinarians. Pruritus is a sensation in the skin that occurs with a number of skin diseases however the list of differential diagnoses for common causes of pruritus that appear clinically similar to CAD is relatively small. Causes of pruritus are often classified into primary diseases,
able to cause pruritus directly, or secondary causes which are diseases (usually infections) that occur as a consequence of the damage to the skin caused by a primary disease. The possibility of several co-existing primary and/or secondary pruritic diseases should be considered. In particular, for the diagnosis of CAD, it is important to determine if the pruritus and erythema are the result of environmental CAD, and/or the presence of hypersensitivity to fleas, and or adverse reaction to food, and/or infections. Often a variety of therapeutic or diagnostic trials are indicated to really determine
If the dog is still pruritic after the above conditions have been ruled out or controlled and it has compatible clinical signs, then it is usually possible to make a tentative diagnosis of atopic dermatitis.
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