Originally appeared as Ask the Vet by Dr. Shawn Ashley in Pug Talk Magazine (March/April/93)
Atopy is genetically determined predisposition towards hypersensitivity reactions to normally innocuous allergens (air-borne protein particles). Offspring inherit these predispositions from their parents, but siblings are not necessarily allergic to the same allergens. It can be found in dogs of any breed, but there are breed predilections, - - Pugs, Boston Terriers, Cairn Terriers, Fox Terriers, West Highland Terriers, English Bulldogs, Dalmatians, Lhasa Apsos, Irish Setters and Miniature Schnauzers.
In humans, atopy is seen primarily as allergic rhinitis (hay fever), asthma attacks, and occasionally pruritic dermatitis. In dogs, atopy is exhibited usually as a pruritic dermatitis as they have more histamine producing cells in their skin. Often the atopic dog may only show chronic otitis externa (red, swollen, inflamed, infected ares). However, in most cases pruritus is the outstanding clinical sign especially of the face, ears, feet, and axillary regions of the body.
Atopy is the second most common cause of allergic dermatitis in the dog (flea bite dermatitis is the number one cause). It is characterized by a hyposensitivity to certain inhaled allergens. These include pollen aeroallergens-grasses, weeds, trees, fungi; environmental allergens-house dust mite, animal danders-cats, birds, sheep's wool; and insect allergens.
Other allergens include smoke, air fresheners, carpet cleaners, etc. Tobacco smoke has been shown to be more of an irritant than an allergen, evoking sneezing attacks; however, severe atopic responses have been documented to other smokable plant preparations such as marijuana.(It should be noted here that all animals are susceptible to the cancerous concerns of second hand smoke, but that is another disease, another subject).
Hallmark signs of atopy include scratching, chewing, biting, licking giving rise to rust discoloration of hair and feet, and rubbing on everything.
The pruritus often precedes any noticeable skin lesions. Combinations of antihistamines, fatty acid supplements, andsoothing hypoallergenic shampoos and conditioners (Hylyt-DVM, Episoother-Allerderm) may be all that is needed for mild seasonal atopic episodes. Short term corticosteroids may be necessary if the itching continues.
If skin lesions occur, oral antibiotics and medicated antipruritic shampoos (Tlux-Allerderm, Nusal-t-DVM) may replace the hypoallergenic shampoos. Otic preparations based on ear swabs and stains will be necessary in those cases involving the ears. In spite of all these efforts the atopic dog may become progressively non-responsive to therapy and a chronic deep skin infection (pyoderma) is developed.
If steroid use is becoming longterm at higher doses and the skin never seems to heal, intradermal skin testing is the only way to achieve a definitive diagnosis and subsequent immunotherapy (weekly desensitizing injections) is the only treatment that addresses the cause, not just the symptoms.