Section: Information In-depth
Many skin diseases of dogs feature pruritus (itching) as a symptom and may appear similar to atopy. Ruling out other causes of pruritus is an important part of establishing a diagnosis.
Diseases that can appear similar to atopy include:
Food allergy in dogs commonly causes a pruritic skin condition. As with atopy, dogs with food allergy often chew their feet, rub their faces and scratch their ears. Thus, the symptoms of food allergy are virtually indistinguishable from those of atopy. One important historical difference to remember is that atopy symptoms usually begin between one and four years of age, whereas food allergy can begin at any age. A dog with an onset of signs that is less than eight months of age or over six years of age, is unlikely to have atopy. Also, atopy is usually well controlled by treatment with corticosteroids (hormones) like prednisone. Food allergy is variably responsive to prednisone; only about 50 percent of affected dogs will respond.
Flea allergy dermatitis is the most common allergic skin disease seen in the United States. Like food allergy, it is variably responsive to corticosteroids. Dogs with flea allergy tend to chew and scratch at their back ends, so lesions are typically seen over the rump, on the belly and between the hind legs. This difference helps to differentiate this disease from atopy. It is possible, however, to see atopy and flea allergy in the same animal.
Scabies is an itchy skin disease of dogs caused by the sarcoptic mange mite. Affected dogs are extremely itchy and often have lesions on their ears, elbows and hocks. Lesions may also be seen elsewhere on the dog. This disease is poorly responsive to treatment with corticosteroids.
Pyoderma (bacterial infection of the skin) is often associated with atopy and other pruritic skin diseases. Chronic self-trauma to the skin breaks down normal defense mechanisms and allows colonization by bacteria leading to infection. Infected skin can be very itchy. Some animals with atopy are only mildly itchy most of the time but may be much worse when they have pyoderma. Less commonly, yeast infections of the skin may be seen secondary to atopy and can also cause the animal to be itchy.
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