Atopy is diagnosed by excluding food allergy, flea allergy, and scabies. However, there are historical clues that increase the likelihood of atopy:
- Age of onset is a helpful clue. Atopy usually develops between 1 and 3 years of age. Therefore, if pruritus starts at less than 1 year of age or greater than 5-6 years of age, then atopy is less likely.
- Location of pruritus is a helpful clue. Pedal and facial pruritus are common in atopic dogs. If neither location is pruritic, then atopy is less likely.
- A skin test is not used to diagnose atopy since even normal dogs can have positive reactions on skin tests. Once food allergy, flea allergy, and scabies are ruled out, a skin test is used to create allergy vaccine.
Since atopy can be managed but not cured, all therapies are needed for the lifetime of the pet in most cases.
Benign symptomatic therapies
Benign symptomatic therapies include antihistamines, essential fatty acids, and once to twice weekly bathing to remove allergens. If these therapies are not effective, then the following options should be considered.
Allergy vaccine therapy
Allergy vaccine therapy is effective in 60-75% of atopic patients. For some patients, vaccine is the only therapy needed. For other patients, vaccine is a tool that allows us to reduce the pet's other oral medications. Vaccine is created specifically for each patient based on either a skin test, a blood test, or a combination of these tests. The owners are taught how to give injections at home. Injections are given every 1-2 weeks once the maintenance phase is reached. Some pets start to show a response at 3-6 months; however, we recommend a full year of vaccine before deciding if it is effective.
Please see cyclosporine. Cyclosporine is used in both dogs and cats. Although cyclosporine use in cats is off-label, we often try cyclosporine in cats before allergy vaccine because skin tests are difficult to interpret in cats.
Oral steroid therapy
Oral steroid therapy is effective in almost all patients. The goal with steroid therapy is to find the lowest dose given on an every other day schedule that keeps the pet's pruritus level tolerable. "Tolerable itch" is an important concept to explain to owners. Tolerable itch is a mild to moderate amount of itch that does not harm the pet's quality of life and allows the use of a lower steroid dose. If the itch level with steroid therapy is zero, then a lower dose of steroids should be used to reduce steroid side effects.
In many dogs, a specific oral steroid product called Temaril-P (a prednisolone, trimeprazine combination tablet made by Pfizer) allows us to use a lower total steroid dose than using prednisone alone.
In cats, we often use oral dexamethasone because the longer duration of action of this steroid allows twice a week maintenance therapy. Twice weekly pilling is often easier than every other day pilling for cat owners
We do not recommend using injectable steroids because these drugs cannot be withdrawn if side effects occur.
Antibiotics and antifungals
Antibiotics and antifungals (oral and/or shampoo versions) should be used as needed to treat any secondary bacterial or yeast skin infections. These infections increase the pruritus level significantly. When a previously well controlled atopy patient has a pruritus flare, check for and treat these infections rather than increasing the steroid or cyclosporine dose.