Over the years various workers have developed and published criteria for diagnosing canine AD (Willemse 1986, Prelaud et al 1988). These criteria were further refined by Claude Favrot and his colleagues following a large study involving over 1000 dogs, published in 2009 and clarified by Olivry in 2010. They are recommended for use in general practice to aid in the diagnosis of AD.
The 2009 Favrot Diagnostic Criteria for Canine Atopic Dermatitis
- Onset of signs under 3 years of age
- Dog living mostly indoors
- Glucocorticoid-responsive pruritus
- Pruritus sine materia at onset (i.e. pruritus without lesions at onset)
- Affected front feet
- Affected ear pinnae
- Non-affected ear margins
- Non-affecteddorso-lumbar area.
If 5 criteria are met the sensitivity is 85% with a specificity of 79%. If 6 criteria are met the sensitivity falls to 58% and specificity increases to 89%. Whilst these criteria could lead to a misdiagnosis in 20% of cases, by ruling out ectoparasitic disease and pyoderma, the specificity can be increased considerably.
All animals should be evaluated for ectoparasites by skin scraping.
Therapeutic trials for fleas and sarcoptic mange (dogs) should be undertaken.
A combination of systematic and topical treatment for pyoderma and Malassezia should be employed if micro-organisms are contributing to the level of pruritus. Specific culture for dermatophytes should be performed when indicated.
Serological testing and intradermal skin testing have no role to play in diagnosing atopic disease or other hypersensitivity disorders. Once the clinical diagnosis has been established, testing for IgE may be appropriate to assist in allergen avoidance or to permit the use of allergen specific immunotherapy as a treatment modality.
In 2011 Dr Favrot and his colleagues produced a set of criteria to help identify cats with non-flea induced allergic dermatitis:
- Presence of at least two body sites affected.
- Presence of at least two of the four clinical patterns:
- Symmetrical alopecia
- Miliary dermatitis Eosinophilic dermatitis
- Head and neck erosions/ulcerations
- Presence of symmetrical alopecia
- Presence of any lesions on the lips
- Presence of erosions or ulcerations on the chin or neck
- Absence of lesions on the rump
- Absence of non-symmetrical alopecia on the rump or tail
- Absence of nodules or tumours
If 5 of the 8 criteria are met a diagnosis of allergic dermatitis is likely although similarly presenting dermatoses (FAD, dermatophytosis, adverse food reaction, neurological and behavioural factors) must be ruled out.
As for dogs, these feline criteria may be useful and practical but it remains essential to eliminate other cause of pruritus to reduce the likelihood of a misdiagnosis.
Similar diagnostic criteria have not, as yet, been established for horses.