Allergic contact dermatitis in the dog. Principles and diagnosis

Allergic contact dermatitis is a rare hypersensitivity disorder in the dog. Clinical diagnosis is not easy. Primary lesions are transient. Secondary lesions caused by chronic inflammation and self-trauma are commonly present on typical areas, especially in sparsely haired regions and on the feet. A presumptive diagnosis can be made based on the history, clinical signs, and positive standardized closed patch testing. Histopathology and basophil degranulation testing may also be helpful in supporting the diagnosis and in identifying the offending allergens. However, a definitive diagnosis can be made only after restriction-provocation testing. With better understanding of the pathogenesis and clinical signs, and with increased availability of diagnostic tests (especially a standardized closed patch test), increased recognition of this dermatosis is expected.