Recent Advances in atopic skin disease
Atopic dermatitis in dogs(CAD) is defined as a genetically-predisposed inflammatory and pruritic allergic skin disease with characteristic clinical features. It is associated most commonly with IgE antibodies to environmental allergens. This is The International Task Force on Canine Atopic Dermatitis’ definition which was drawn up in the early part of the century.
Muller and Kirk’s Small Animal Dermatology defined it as a genetically programmed disease of dogs and cats in which the patient becomes sensitised to environmental antigens which in non-atopic animals create no disease. It has been defined as a reaginic antibody mediated disease.
Atopic dermatitis is a rule out disease based on eliminating the other differential diagnoses in a dog exhibiting appropriate clinical signs and a supporting history.
In the 1980s, Willemse introduced the concept of major and minor criteria in assisting the diagnosis of atopic dermatitis. This has been superceded by Favrot’s team with a new set of diagnostic criteria including:
Age at onset under 3
A corticosteroid-responsive dermatitis
Chronic or recurrent yeast infection
Affected front feet
Time mostly spent indoors
Non-affected ear margins
Non-affected dorsolumbar area
Once diagnosis has been made additional tests can be performed to detect the allergens involved in the allergy. Many studies now show similar specificity and sensitivity to skin testing and IgE serology. I will often use both tests before deciding on the allergens to put in the vaccine.
Intradermal skin testing
Certain drugs can affect the results of a skin test including corticosteroids, cyclosporine, acepromazine, antihistamines and essential fatty acids. Approximately 20% of dogs will not react to a skin test even though the diagnosis of atopy has been made. The most common positive results in the UK are to dust mites.
Several tests are available in the UK for measuring allergen-specific IgE. The most common test in Europe is based on the use of IgE receptor components instead of just IgE. In one study it was suggested that 20% of relevant allergens would be missed if only serology was used. However, serology is useful when it is difficult to get the dog off steroid medication as the serology results are less sensitive to the use of concomitant steroids compared with the skin test
A multimodal approach to treatment is considered best. This treatment protocol would include:
Protecting the epidermal barrier
Treating the environment for dust mites
Antimicrobial treatment as appropriate
Anti- pruritic agents
Allergen specific immunotherapy.
Amongst the many recent advances in the treatment of atopy is a steroid based spray. It contains hydrocortisone aceponate. This steroid breaks down as it moves through the skin and has no systemic action, although, it can thin the skin with prolonged use. It can also be used whilst skin testing as long as one does not treat the skin where the test is to be performed.
Oclacitinib is a novel Janus kinase inhibitor that has activity against canine pro-allergic and pro-inflammatory cytokines. Its preliminary use in dogs with atopic dermatitis have given impressive results but supply chain problems will limit its use until well into 2015.
Recently, the use of sub-lingual allergen specific immunotherapy (SLIT) has become more common in the UK. It has been suggested that it may work in patients when traditional injection protocols have failed.
Yet more ways of diagnosing and treating atopic dermatitis will come to market in the next few years to help us treat this intractable, frustrating condition.