The short answer
Canine atopic dermatitis is diagnosed clinically, from history, signalment, clinical signs and the exclusion of other itchy skin diseases, and intradermal or serum IgE tests are used only after that diagnosis is made, mainly to choose allergens for immunotherapy [2][3]. The 2015 ICADA treatment guidelines divide management into acute flares, chronic disease and prevention of relapses [1]. For flares the guidelines name topical and oral glucocorticoids and oclacitinib, and for chronic disease they add ciclosporin and, where available, injectable recombinant interferons [1]. The Merck Veterinary Manual also describes lokivetmab and ilunocitinib, which the 2015 guidelines do not cover [3].
Key takeaways
- An ICADA diagnostic panel lists four rule-out steps before a clinical diagnosis: fleas, other ectoparasites, staphylococcal and Malassezia infection, and cutaneous adverse food reaction [2].
- The ICADA treatment panel states that "'allergy tests' must never be used to diagnose AD" [1].
- The ICADA diagnostic panel estimates that between 10 and 30 % of dogs with clinically confirmed atopic dermatitis may show a negative intradermal test [2].
- The 2015 treatment guidelines rate oral glucocorticoids, ciclosporin and oclacitinib as effective for chronic disease, with the strongest recommendation grade (SOR A) [1].
- According to the 2015 guidelines, allergen-specific immunotherapy and proactive intermittent topical glucocorticoids are the only interventions likely to prevent or delay flares [1].
- The Merck Veterinary Manual describes allergen-specific immunotherapy as the only treatment that can change the dog's immune response to allergens [3].
Doses on this pageEvery dose below is quoted from the cited source. Verify against the current label/formulary and the patient's full clinical picture.
Definition and affected dogs
According to the Merck Veterinary Manual, ICADA in 2023 defined the disease as "a hereditary, typically pruritic, and predominantly T-cell-driven inflammatory skin disease involving interplay among skin barrier abnormalities, allergen sensitization, and microbial dysbiosis" [3]. The same chapter uses "atopic-like dermatitis" for cases that clinically resemble IgE-mediated atopic dermatitis but lack detectable IgE sensitization [3].
Merck gives a usual age of onset between 6 months and 3 years, with no sex predisposition [3]. It names the West Highland White Terrier among predisposed breeds and notes that breed prevalence varies with the genetic pool and region [3]. Signs may be seasonal, year-round, or year-round with seasonal worsening [3].
Clinical presentation
Itch comes first. The ICADA diagnostic panel lists scratching, rubbing, chewing, licking, scooting and head shaking as ways it shows, and says early itch may occur with no visible lesions [2]. The panel names the following as the usual sites [2]:
- the face
- the inner surface of the ear flaps
- the ventrum
- the armpits
- the groin
- the perineum
- the lower limbs
It also describes breed patterns [2]. In French bulldogs these include the eyelids and flexural surfaces. In West Highland white terriers they include the dorso-lumbar area, lips and flexural surfaces.
Merck describes primary lesions (the first lesions, before self-trauma) as uncommon: red flat spots, patches and small bumps [3]. Chronic cases develop secondary changes from scratching and infection, including hair loss, thickened skin (lichenification), darkened skin and crusts [2]. Merck adds that secondary Staphylococcus and Malassezia infections are common and that recurrent ear infection may be the only sign in a small number of dogs [3].
Diagnosis
Ruling out look-alike conditions
The ICADA diagnostic panel says no single approach should be used alone, because each can lead to misdiagnosis [2]. Its flea step makes three points [2]:
- Flea allergy lesions tend to sit over the lower back, tail base and back of the thighs.
- Flea pupae can survive up to 174 days.
- Fast-acting systemic adulticides may reduce itch faster than topical products.
For scabies, the panel recommends a trial treatment in very itchy dogs, partly because Sarcoptes mites can cross-react with house dust mites on allergy tests [2].
For year-round itch or gut signs, the panel says food reactions can only be excluded by a strict elimination diet fed for at least 8 weeks, with relapse on re-challenge confirming food involvement [2]. The 2015 treatment guidelines cite a critically appraised topic finding that an 8-week elimination diet should bring remission in more than 90 % of dogs with food reactions [1]. The diagnostic panel lists common compliance failures, including treats, flavoured medications, chewable parasite preventives and eating other animals' faeces. It also notes that hydrolysed diets are based on chicken or soy [2].
Favrot's criteria
The ICADA panel describes a set of clinical criteria drawn from a large case series. In Set 1, meeting five of eight criteria gave a sensitivity of 85.4 % and specificity of 79.1 %. Requiring six raised specificity to 88.5 % and dropped sensitivity to 58.2 % [2]. The criteria are [2]:
- onset before age 3
- living mostly indoors
- itch that responds to corticosteroids
- recurrent yeast infections
- affected front feet
- affected ear flaps
- sparing of the ear margins
- sparing of the lower back
The panel warns that "these criteria should not be used in isolation" as a diagnostic test [2]. Merck notes they do not apply to food-induced disease [3].
Allergy testing and its pitfalls
The ICADA panels say intradermal testing (IDT) and allergen-specific IgE serology (ASIS) confirm hypersensitivities in dogs already diagnosed clinically, mostly to formulate immunotherapy [1][2]. Healthy dogs and dogs with other itchy diseases can test positive [1]. The 2015 treatment guidelines cite a four-laboratory comparison with large variation in serology results, except for mites [1]. The diagnostic panel says IDT and ASIS should not be used to diagnose food reactions, citing IDT sensitivity of 10 to 33 % for food [2].
The diagnostic panel lists these suggested withdrawal times from an evidence-based review, while noting they vary with dose and duration [2]:
| Drug | Before IDT | Before ASIS |
|---|
| Antihistamines | 7 days | probably not needed |
| Short-acting oral glucocorticoids | 14 days | none |
| Long-acting injectable glucocorticoids | at least 28 days | <28 days |
| Topical glucocorticoids | 14 days | none |
| Ciclosporin | probably not needed | none |
How the guidelines classify management
None of the three sources gives a formal severity staging scheme. The 2015 ICADA treatment guidelines organize care into acute flares, chronic disease and relapse prevention. They say that plans vary between dogs and over time in the same dog [1]. Merck states that options depend on severity and on whether itch is seasonal or year-round [3].
Treatment of acute flares
The 2015 ICADA guidelines start with finding and removing the flare trigger, such as allergen exposure, food or flea bites. They then call for treating bacterial or yeast infection under national or international antimicrobial guidelines [1]. They rate two named emollient shampoo regimens as giving a modest benefit (SOR B), probably greatest in mild cases. They also advise watching for a drying or irritating effect of topical antimicrobials, especially shampoos, that might induce a flare [1].
For drug control, the panel gives hydrocortisone aceponate spray an SOR A rating. It says daily topical use at the same site over the long term will nearly always cause skin thinning [1]. It states that oral prednisolone, prednisone or methylprednisolone "given at 0.5 to 1.0 mg/kg per day, in one or divided into two doses" is likely to help severe or extensive disease [1]. It does not recommend long-acting injectable glucocorticoids [1]. Oclacitinib is rated SOR A for rapid reduction of lesions and itch. The panel calls combined oral glucocorticoids and oclacitinib "likely contraindicated" on theoretical immunosuppression grounds [1]. If a dog does not improve quickly on either drug, the panel advises reconsidering the diagnosis or looking for complications [1].
The panel considers antihistamines to offer at most a small benefit, best given before a flare. It says oral fatty acids and calcineurin inhibitors act too slowly for flares [1]. Merck describes oclacitinib as acting on itch within 24 hours [3]. It describes lokivetmab, an antibody against the itch cytokine IL-31, as having a quick onset suitable for flares [3].
Long-term control
Flare factors and skin care
For chronic disease, the 2015 guidelines call for year-round flea control [1]. They note that house dust mite control might be effective in sensitized dogs. They also say clinicians should consider repeating diet trials when a previously well-controlled dog relapses [1]. Because of storage mites, they advise storing dry food in clean sealed containers away from warm, humid areas [1].
The panel describes bathing at least once weekly with a mild shampoo and lukewarm water as likely beneficial [1]. It says oral essential fatty acids may give small gains and may take two months to show any effect [1]. Merck cites studies in which fatty acids reduced the doses needed of glucocorticoids, ciclosporin and oclacitinib [3].
Systemic and topical drugs
The 2015 panel states that oral glucocorticoids should be used at 0.5 mg/kg once to twice daily to induce remission, then tapered to the lowest effective dose and frequency [1]. For oral ciclosporin, the panel states it should be administered at 5 mg/kg once daily until signs are controlled, which usually takes 4 to 6 weeks, and then tapered in dose or frequency [1]. The panel says prednisolone can be added for the first 3 weeks to speed onset [1].
It lists oclacitinib "at 0.4 to 0.6 mg/kg twice daily for 14 days and then once daily thereafter," and notes the drug is not approved for dogs under 12 months [1]. The panel advises against prolonged combinations of any of these three drugs [1]. It says topical glucocorticoids are used intermittently after a daily induction phase. Because of cost, it reserves tacrolimus mainly for dogs with visible skin thinning [1].
The 2015 guideline does not cover lokivetmab or ilunocitinib, so Merck is the only source here covering them. Merck reports no age restriction or known drug interactions for lokivetmab [3]. For ilunocitinib, it lists a 12-month minimum age, contraindication in serious infection and vaccination timing restrictions [3].
Allergen-specific immunotherapy
Merck describes subcutaneous and sublingual routes and gives a response time of 3 to 12 months [3]. It cites a 2022 retrospective study of 664 dogs given subcutaneous immunotherapy. In that study, about 60 % of dogs treated for at least 9 months had a decrease in itch greater than 50 % [3]. About half of the improved dogs still needed other medication, and concurrent glucocorticoids appeared to reduce response [3]. Merck also cites a 2020 study suggesting the sublingual route may be inferior to subcutaneous or intralymphatic immunotherapy, while other studies reported good results [3]. Increased itch is the most common adverse effect, and anaphylaxis is very rare [3].
Monitoring, prognosis and client communication
The 2015 panel reports no consensus on routine laboratory monitoring during long-term ciclosporin or oclacitinib, but says tests should be run if systemic illness develops [1]. It also says dogs on long-term oral glucocorticoids should have periodic urinalysis and urine culture [1]. Merck states that the disease "cannot be cured" but can usually be managed, and that it needs lifelong care and regular rechecks [3].
Merck's immunotherapy section makes three points relevant to client conversations [3]:
- Owners should be told that treatment needs at least 12 months before its response is judged.
- Owners should give each dose when they are able to watch the dog for at least 30 minutes afterward.
- Response is best assessed by comparing disease between similar seasons.
