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A clinician’s guide to managing atopic dermatitis in dogs
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  1. Natalie Barnard

Abstract

Background: Atopic dermatitis is a complex condition in dogs that requires lifelong management. As such, veterinarians and owners must work together to manage these difficult cases to get the best clinical outcome for the animal.

Aim of the article: This article provides a guide to the different management options available for dealing with cases of atopic dermatitis in dogs, and things to consider when deciding on the best course of action.

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Natalie Barnard qualified from the Royal Veterinary College (RVC), London in 2001. She spent two years in general practice before returning to the RVC to undertake a three-year residency in veterinary dermatology. She attained her RCVS certificate in veterinary dermatology in 2006 and her European diploma in veterinary dermatology in 2009. She recently set up a dermatology referral service at Highcroft Referrals in Bristol, where she currently works.

Key learning outcomes

After reading this article, you should:

  • Understand that each patient should be treated as an individual and there is no blanket protocol for managing patients with atopic dermatitis;

  • Understand the concept of pruritic threshold;

  • Understand what flare factors are and their importance when managing cases of atopic dermatitis;

  • Understand the importance of topical therapy when managing cases of atopic dermatitis with particular reference to controlling flare factors;

  • Have a knowledge of which treatments for atopic dermatitis have good, fair and little evidence for their use.

Atopic dermatitis is a genetically predisposed inflammatory and pruritic skin disease with characteristic clinical features, most commonly directed against environmental allergens such as house dust mites and pollens (Halliwell 2006). The management of this condition in dogs is complex as there are many patient and client factors to consider. In addition there is also a need to deal with secondary conditions which can exacerbate the clinical signs, including ectoparasites and infections. This is a lifelong condition and it is vital that veterinarians and owners work together to manage these complex cases to get the best clinical outcome.

What should be done once atopic dermatitis has been diagnosed?

Once a clinical diagnosis of atopic dermatitis has been made, the next step is to find the best way to manage your patient’s clinical signs. There are many different treatment options available and each patient should be treated as an individual. There is no blanket protocol that will be suitable for all dogs with atopic dermatitis and it is important to explain this to the owner at the outset, as then they will be more understanding when treatments fail and something new is tried. As a general rule, we like to try and use the least amount of medication possible that will control the patient’s clinical signs. Educating the client about atopic dermatitis is vitally important in managing the disease and is something that is often overlooked. Sometimes writing a handout for the clients can be useful.

What is the pruritic threshold and how does it affect my decision making when selecting treatments?

The pruritic threshold is an important concept for a patient with atopic dermatitis. The concept for a threshold of pruritus relates to the presence of a multitude of stimuli (such as colonising bacteria, yeast and ectoparasites) that might contribute to the level of itch of the individual patient (Marsella and Sousa 2001, Miller and others 2013). The theory of the ‘pruritic threshold’ hypothesises that any individual is able to tolerate some pruritic stimulus without becoming pruritic, but when multiple stimuli are present at the same time, the summation of their effects exceeds the threshold of pruritus and so the patient will become pruritic (Fig 1). This is why in some cases when you treat the infections present, the patient will often improve considerably. Other factors such as chronic changes to the skin (eg, lichenification) and environmental factors, including overuse of various topical therapies, all contribute to the summation factors that cause pruritus.

Fig 1:

Graph demonstrating the pruritic threshold. It demonstrates the effect of multiple causes of pruritus adding up the level of pruritus that is seen clinically. It also shows how you can improve a dog’s clinical signs of pruritus by treating flare factors, such as pyoderma and Malassezia dermatitis

Importance of flare factors and secondary conditions

Flare factors, such as ectoparasites and skin infection, can exacerbate the patients’ clinical signs and it is important that these are effectively identified and controlled when managing our allergic patients. As discussed above, flare factors may take the dog over their pruritic threshold and cause an increase in pruritus; if we do not identify what has caused this increase in pruritus we may mistakenly just increase the anti-inflammatory treatment to help control the pruritus or assume it has failed. In seemingly well-controlled atopic dogs, clients can become complacent and reduce the frequency of topical therapy or become less vigilant when administering ectoparasite control. In some cases, clients may also be reluctant to administer ectoparasite control due to concerns with the reported environmental impact of some treatments. Therefore, it is important that the relevant questions are asked to determine if this has happened when assessing these patients for flare ups.

Ectoparasites

We usually advise that all dogs with atopic dermatitis are maintained on a strict flea control programme, regardless of whether they have flea allergic dermatitis; we know that the atopic status predisposes dogs to develop hypersensitivity to flea bites if repeatedly exposed. Flea bite hypersensitivity is also a well-known flare factor for patients with atopic dermatitis (Olivry and others 2010). Clients need to be educated about the life cycle of the flea so that they understand the importance of environmental control as well as on-animal treatment. In addition, we must be aware that all in-contact animals can act as potential sources of ectoparasites, including dogs, cats, rabbits and wildlife and so the flea control programme should also consider any in-contact animals.

Management of the environment is also crucial and regular management measures may include using a household spray containing an adulticide and insect growth regulator one to two times a year alongside regular vacuuming. If clients are reluctant to spray the environment, then selecting an on-animal treatment with a rapid speed of kill (ideally within 24 hours) will help to prevent the development of the flea life cycle in the environment. Or you should advise that they choose an on-animal product, such as selamectin, which has ovicidal and larvicidal effects in addition to being an adulticide (McTier and others 2000).

Infection

Skin infection

Skin infection caused by yeast and bacteria are important flare factors in dogs with atopic dermatitis (Olivry and others 2010) and any infection will take most patients over their pruritic threshold. Atopic dogs are much more likely to develop secondary skin infections partly because they have a defective skin barrier function (Olivry and others 2010).

Pyoderma

Pyoderma is the term given to bacterial skin infections in the dog. Over 90 per cent of bacterial infections in dogs are caused by a Staphylococcus pseudintermedius (Morris and others 2017). This is a Gram-positive coccoid bacterium, which is a normal resident of canine skin. Superficial pyoderma involving the infundibular portion of the hair follicles and epidermis is commonly observed in canine patients with atopic dermatitis. Clinical signs of infection include papules, pustules and epidermal collarettes (Figs 2, 3). Short-haired dogs may present with patchy alopecia on their hair coat.

Fig 2:

Appearance of a superficial pyoderma on the ventral abdomen of a dog. Note the erythema, papules and pustules

Fig 3:

Epidermal collarettes are visible on the ventral abdomen of this dog with superficial pyoderma

Patients with pyoderma are usually managed with a combination of systemic antibiotics and topical therapy. Although, it should be noted that in some patients topical therapy alone will be sufficient. It is important that antimicrobials are used responsibly and ideally treatment choice should be guided by clinical history, physical examination and cytological findings. Suitable first-line antibiotic treatments for superficial pyoderma caused by S pseudintermedius include:

  • Clindamycin,

  • Cefalexin, and

  • Potentiated amoxicillin.

It is beyond the scope of this article to cover the treatment of pyoderma extensively and the reader is advised to consult other references if further information is required (Frosini and Loeffler 2020).

Malassezia dermatitis

Malassezia species are a commensal yeast found on the skin and hair coat of most dogs. Malassezia dermatitis is a common flare factor for patients with atopic dermatitis due to their defective barrier function (Olivry and others 2015, Santoro and others 2015, Bond and others 2020). Commonly affected areas are the ears and skin folds. Clinically affected patients are often intensely pruritic. Affected skin may be erythematous, alopecic and greasy. Over time, the skin may develop more chronic changes such as hyperpigmentation and lichenification. Topical therapy is the best way to control Malassezia dermatitis and prevent a recurrence of this flare factor. Many shampoos are available; in my opinion, shampoos containing both 2 per cent miconazole and 2 per cent chlorhexidine (Malaseb shampoo; Dechra, Adaxio shampoo; Ceva), or 3 per cent chlorhexidine (Microbex shampoo; Virbac, Douxo Pyo S3 shampoo; Ceva) are the most useful to manage these cases. However, in some cases topical therapy is not possible and so off-licence systemic therapy with itraconazole or ketoconazole may be considered. It is important to get informed consent from the owner if electing to use these systemic products as these products are not licensed for use in the dog.

Otitis externa

Otitis externa is commonly observed as a manifestation of a flare up in our atopic patients. Cytology should be performed in all patients presenting with otitis to facilitate appropriate treatment. Some atopic patients may present with an allergic otitis when no microorganisms are present on cytology. In these cases, treatment with a topical glucocorticoid such as triamcinolone (Recicort; Dechra) may be required to control the inflammation. Regular ear cleaning once or twice weekly is also a good way to prevent relapsing microbial overgrowth in atopic patients.

Topical therapy

Topical therapy is very valuable when managing patients with atopic dermatitis. It can be used to treat infections when present, but it can also be used to prevent infections from recurring. There are a wide variety of products on the veterinary market. The main issue with topical therapy can be owner compliance. It is useful to get a member of your team to discuss in detail with the client how to use the topical therapy you are dispensing.

Bathing

Medicated shampoos can be extremely useful when managing infections in dogs with atopic dermatitis. Generally, these products would be used twice weekly, at least initially, or when infection is present; as the infection resolves and atopic dermatitis comes under control the frequency of bathing can be reduced. You should also stress to the client the importance of adhering to the contact times given for the shampoo product when they are dispensed.

Leave on mousse (foam) products

Mousse products that are massaged into the skin and hair coat are now widely available on the veterinary market. Clients find these products easy to use and less time consuming when compared to bathing. I tend to prescribe these in conjunction with shampoos and advise for them to be used in-between bathing.

Medicated wipes and pads

Medicated wipes and pads are especially useful for clients to clean their dog’s interdigital skin, lip and facial folds. Using wipes can be less time consuming then bathing. I advise using these products in conjunction with bathing or for long-term maintenance cleaning.

Ear cleaning

There are many ear cleaners available on the veterinary market. If a patient with atopic dermatitis suffers from recurrent otitis then regular ear cleaning can be a good way to prevent this from happening. Nearly all products available have antimicrobial action and the choice of ear cleaner prescribed will depend on a variety of client and patient factors, such as the type of infections the patients suffers from, the pH of the ear cleaner, the ability of client to apply the cleaner, any reported contact reactions seen with ear cleaners.

How can we actually control atopic dermatitis?

Avoidance of the allergen

Avoidance of the allergen is cited in many text books as being a way to treat or manage atopic dermatitis. However, the majority of patients affected by atopic dermatitis are allergic to house dust mites which are hard to avoid (Nuttall and others 2006). A reduction in allergen load may be possible, although it is unclear whether this benefits the patient clinically. Various environmental flea sprays have a licence for lowering house dust mite numbers and so may also be useful in house dust mite-allergic animals (Swinnen and Vroom 2004). Other measures that can lower house dust mite exposure include:

  • Keeping the animal outside,

  • Minimising carpets in the house, and

  • Not allowing the dog to sleep in the bedroom.

However, these measures are often unpopular with both clients and patients, and again there is currently no clear proven clinical benefit of these measures.

Anti-pruritic and anti-inflammatory treatments

Once skin infections and flare factors have been controlled, some patients will require additional anti-inflammatory or anti-pruritic therapy to manage their atopic dermatitis. The licensed treatment options for atopic dermatitis will be discussed below, based on their evidence and efficacy as previously reported by the International Committee on Allergic Diseases of Animals (Olivry and others 2010, 2015).

Treatments with good evidence for efficacy

Glucocorticoids

Glucocorticoids (prednisolone, methylprednisolone, dexamethasone) are widely used for the treatment of atopic dermatitis and are very effective at rapidly controlling pruritus in most cases. The drugs most commonly used are oral prednisolone (0.5 mg/kg once daily, tapering to every other day) or methylprednisolone (0.4 mg/kg once daily, tapering to every other day) in dogs. We should always try to find the lowest dose of alternate day steroid that controls the animal’s clinical signs in favour of using daily treatment. Adverse effects can include:

  • Polydipsia,

  • Polyuria,

  • Polyphagia,

  • Lethargy,

  • Exercise intolerance,

  • Muscle wasting,

  • Panting,

  • Secondary infections, and

  • Calcinosis cutis.

Dogs on long-term glucocorticoid treatment should be regularly monitored, at least every six months, with blood biochemistry and urinalysis.

Topical steroids

Topical steroids (Cortavance; Virbac, Dermalon; Dechra) can be extremely beneficial in some cases, especially when the pruritus is localised to a specific area or when short-term treatment is required. Care should be taken with some products, as prolonged use can thin the skin.

Ciclosporin

Ciclosporin (various liquid and capsule formulations are available) is another potent drug that inhibits the activation of cells capable of inducing and effecting the allergic inflammatory response. It is very effective in patients with atopic dermatitis. It is important to realise that it can take four to eight weeks for the maximum benefits of this drug to be seen, and so at least an eight-week trial of daily treatment should be undertaken in the first instance. Adverse effects are mainly gastrointestinal (ie, vomiting and soft faeces). These signs are usually mild and self-limiting, occurring in the first few weeks of treatment. Other adverse effects include gingival hyperplasia, hypertrichosis, anorexia and pruritus. It can be cost prohibitive for some owners.

Oclacitinib

It has been reported that canine IL-31 induces pruritic behaviour in dogs and plays an important role in the pathogenesis of atopic dermatitis in dogs. Oclacitinib (Apoquel; Zoetis) selectively inhibits Janus kinase (JAK)-1-dependant cytokines, which in turn leads to a reduction in IL-31 and pruritus. This medication is licensed for use in the management of atopic dermatitis in the UK in dogs older than one year of age. It is well tolerated by most patients and there is good evidence for its use. Patients will initially receive the treatment twice daily for 14 days and then the dose is reduced to once daily. It is common for some patients to have a slight increase in pruritus when the dosing regime is reduced, but oclacitinib is not licensed for twice daily use long term. It is advised that patients receiving treatment with oclacitinib have regular blood monitoring as in some cases leucopenia has been documented (Forsythe and Jackson 2020).

Lokivetmab

Lokivetmab (Cytopoint; Zoetis) is a caninised monoclonal antibody treatment for dogs which selectively binds to and neutralises IL-31. It is a licensed treatment for atopic dermatitis to help control the pruritus in these dogs. In the UK, it is given subcutaneously as a monthly injection and has a rapid onset of action. It is effective in many, but not all, atopic patients. This treatment is licensed for use in dogs from eight weeks of age.

Treatment with fair evidence for efficacy

Allergen-specific immunotherapy

Allergen-specific immunotherapy involves subcutaneous injection or sublingual administration of relevant allergens at regular intervals and in increasing amounts until the target maintenance dose is reached. The allergens included in the immunotherapy are based on the results of allergen testing and it should be remembered that approximately 10 per cent of patients with atopic dermatitis will not have positive reactions on allergen testing. The way in which allergen testing has been performed (intradermal testing [Fig 4] or allergen-specific IgE serology) does not affect treatment outcome in patients on immunotherapy.

Fig 4:

Intradermal test on a dog. Note the large wheals present on the top row of the test. The very first wheal (top left) is the histamine-positive control

The exact protocol will vary depending on the type of allergen-specific immunotherapy used. The success rate of this treatment varies between individuals, and is between 52 and 77 per cent when using subcutaneous allergen-specific immunotherapy and 40 per cent with sublingual immunotherapy. The treatment works by causing a long-term immunological shift from a Th2 response to a Th1 response and the development of immunological tolerance (Mueller and others 2018). It can take many months before the benefits of this treatment are evident and so additional anti-inflammatory therapy in the early stages of treatment may often be required. Treatment needs to be given for at least 12 months before the outcome is evaluated; for this reason, it is important that animals on immunotherapy are monitored regularly to assess their progress and ensure that any flare factors are treated appropriately.

When starting a course of allergen-specific immunotherapy, it is usually advised that the injections are administered at the veterinary practice and the patients observed for at least 30 minutes after each injection to ensure no adverse reaction occurs. Anaphylactic shock occurs rarely, but when it does it is an emergency and requires immediate treatment. Once the full dose is reached, if no adverse reactions have been seen then it is possible for your client to be taught to administer the vaccine at home.

If the allergen-specific immunotherapy is effective, treatment will generally need to be continued for life. However, there are some reports of dogs that have stayed in long-term remission with cessation of therapy (Mueller and others 2018).

Treatment with little or no evidence

Antihistamines

There is a lack of convincing evidence for using antihistamines to treat atopic dermatitis, with the exception of hydroxyzine (2.2 mg/kg three times a day) and cetirizine (0.5 to 1 mg/kg once daily) (Olivry and others 2015). Antihistamines should be trialled for a period of two weeks. They are well tolerated, although in some cases sedation may be seen. Antihistamines appear to be of little benefit in acutely pruritic dogs.

Essential fatty acids

Supplementation with essential fatty acids causes an alteration of the composition and function of the epidermal lipid barrier, which is thought to be beneficial in managing some cases of atopic dermatitis. It can take several months for the benefits of these products to be seen. There are a wide variety of products available on the veterinary market.

How to decide which treatment course is right for your patient?

There is no blanket treatment for atopic patients, so they all need to be treated individually. When deciding what treatment to prescribe, it is important to discuss all the options with the client and to make a decision based on the patient’s clinical signs, and patient and client factors. Things to consider include:

  • Severity of the patient’s disease,

  • Owner finances,

  • Time commitments, and

  • Handling restrictions.

It is important that the client realises that they may need to trial several treatments before the correct regime for their dog is found. Recommendations have been published which can help make decisions regarding what treatment to use for chronic and acute flare ups (Olivry and Banovic 2019), but ultimately the medications used depend on many variables and so this will be a clinical decision depending on the case. It is also important that the expectations of the client are managed. This is a lifelong condition and flare ups are to be expected, even in the best-controlled patient. In order to manage these cases effectively, follow up, ideally with the same vet in the practice, is essential. Building a good relationship with your client will help you to manage these cases and educate the client.

Summary

Atopic dermatitis in dogs is a challenging disease to manage and currently a multimodal approach is required to obtain good control of the skin disease. The exact combination of therapy should be tailored to suit the patient and client, and involves considering many different factors including cost, adverse effects and severity of the patient’s disease.

References

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