Contact Dermatitis in Dogs

Contact Dermatitis in Dogs

By: Dr. Rosanna Marsalla

Section: Veterinary Care In-depth

Diagnosis In-depth

  • Diagnosis is based on clinical signs, distribution (variable depending on the type of substance involved), resolution of clinical signs with avoidance, and recurrence of clinical signs with re-exposure. Implicating a specific allergen is difficult and requires cooperation with the owner to identify possible sources.

  • Contact allergy can be differentiated from inhalant allergy (atopy) by the persistence of a primary papular eruption (red bumps) after appropriate antibiotic therapy. In addition, contact allergy completely resolves with confinement whereas atopy does not.

  • Boarding the animal at the hospital for one to two weeks is recommended to accomplish avoidance. Animals should be shampooed before beginning confinement to remove possible residual material from the skin.

  • Patch testing can also be used to diagnose contact allergy.
    Patch testing is difficult and time-consuming but allows identification of the specific substance responsible for clinical signs. The skin on the chest wall is clipped one to two days before the test and potential allergens are applied in close contact with the skin for 48 hours. Thorough bandaging is the best way to achieve contact with the allergen (closed patch test). An open patch test consists of applying the potential allergen to the inner part of the ear and observing the skin for 48 hours.

    Specialized devices called Finn chambers may be used to apply the suspected allergen. A positive reaction is indicated by the appearance of edema (soft swelling) and a papular eruption (red bumps) 24 to 48 hours after application of the allergen.

  • Microscopic pathology. Skin biopsies show inflammation around blood vessels and swelling of cells in the epidermis.

     
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