Canine Atopic Dermatitis
Allergies, fleas, dermatitis, a new shampoo - what is it that makes our dogs scratch? And scratch, and scratch, and scratch. WDJ explores possible causes and solutions.
[Updated January 30, 2019]
In late autumn, we closed our pool, an annual event that all four of our swim-loving dogs dread. They will swim as long into the fall season as we allow and I am pretty certain that our Toller, Chippy, would bring out an ice pick and break his way through the ice if he could. In addition to the daily joy, excitement, and happiness that our pool brings to us all, we have found that it has had an additional benefit for some of our dogs. The pool and the daily swims that it provides help to keep itchy dogs from itching all summer long.
Over the years, several of our dogs have suffered from atopic dermatitis (also known as atopy). This is not unusual given that we have Golden Retrievers (a breed that is genetically predisposed to atopy) and we live in the Midwest, an area with lots of allergens for hypersensitive dogs to react to.
We have successfully managed this using frequent bathing, topical medications, and when absolutely necessary, short periods of oral (systemic) medication. And now, we also have the pool. Once our dogs started to have daily swims, we found that this form of frequent bathing kept allergy signs at bay throughout the summer, simply by its ability to physically reduce exposure to allergens and to cleanse the skin.
This benefit is not that surprising because, according to two reports (See here and here) by an international task force on canine atopic dermatitis, frequent bathing of dogs, with the specific purpose of removing and reducing exposure to allergens, is identified as one of the most important factors in relieving pruritus (itchiness). Indeed, the task force has quite a bit more to say about effective and not-so-effective approaches to managing itchy dogs.
In 1999, the American College of Veterinary Dermatology (ACVD) established a committee to study canine atopic dermatitis (hereafter CAD). The initial group spent two years reviewing existing knowledge about CAD and published its findings in 2001. That collection of 24 papers provided practicing veterinarians and dermatologists with up-to-date information about the diagnosis, treatment, and management of CAD.
The committee was eventually expanded to include international representation, and its name was changed accordingly, to the International Committee on Allergic Diseases of Animals (ICADA). Now comprised of veterinary dermatologists from around the world, the committee has a series of objectives. One of the most important is to develop and distribute a set of practical guidelines for veterinarians to use when diagnosing and treating CAD. The first set of these guidelines was published in 2010 and recently, a revised edition was made available.
A central component of these guidelines is that they follow the tenets of evidence-based medicine. This means that the committee recommends only procedures and treatments that have supporting scientific evidence and that they systematically rate the scientific merit of that evidence. Naturally, there is a lot of information in these reports that is of interest primarily to researchers and practicing veterinarians. However, there is also an abundance of helpful information for owners who wish to learn more about CAD and about how to best manage this disorder in their dogs.
CAD is a Diverse (and Complex) Disorder
The ICADA’s most recent description of CAD is a genetically predisposed pruritic (itchy) and inflammatory skin disorder. It is most commonly triggered by one or more types of environmental allergens such as dust mites, pollens, and molds. Although the actual sequence of events that leads to a chronically itchy dog is complex, the general progression involves these steps:
1. Exposure to the allergen (or allergens). These either are absorbed through the dog’s skin, are inhaled, or, when a food allergy is the cause (see below), are consumed. Note: Recent evidence suggests that absorption of allergens across the skin, called percutaneous absorption, may be the primary trigger of the allergic response in atopic dogs (See here).
2. This exposure causes an immune system response in the body, which includes the production of a cascade of immune factors and inflammatory agents. One of these factors is allergen-specific IgE, which is considered to be a hallmark indicator of CAD.
3. IgE migrates from the bloodstream to the dog’s skin, where it binds to mast cells (a type of immune cell) and to certain types of nerve cells. When the dog is exposed again to the same allergen, the immunological reaction is amplified and now involves both immune cells and the nervous system. This “neuroimmodulary” response is the major cause of the intensely pruritic (itchy) response that a dog with CAD experiences.
4. Without treatment for the intense itching, the dog begins to scratch, rub, and bite at the affected areas, which causes breaks in the skin, inflammation, and the development of sores and infections. Breaks in the skin (changes in the skin’s integrity) allow more allergen access, which further ratchets up the immune response. The result is a vicious and unending itch-inflammation cycle.
The genetic component of CAD means that certain breeds of dogs are at greater risk for developing the disorder, including Golden Retrievers, Labrador Retrievers, Lhasa Apsos, Wire Fox Terriers, West Highland White Terriers, Boxers, and Bulldogs.
Although not completely understood, the underlying mechanisms that make certain individuals more susceptible to CAD include being born with skin and an immune system that are hyper-responsive to allergens, having a highly sensitive (i.e., easily triggered) inflammatory response, and having a reduced ability to arrest or slow down this response.
CAD and Food Allergy
The ICADA recognizes the complexity of the relationship between CAD and food allergies (technically referred to as “cutaneous adverse food reactions”). Although not true for all dogs, some dogs with CAD can also have food allergies or develop food allergy at a later point in time. Difficulties lie in the fact that the clinical signs of food allergy and CAD can be indistinguishable in a given dog, making diagnosis of either disorder very challenging for veterinarians.
Currently, the ICADA recommends testing a dog for food allergy when the signs of CAD are chronic and non-seasonal. Food allergy should also be suspected in dogs with previously well-controlled CAD who show a sudden return (flare) of symptoms that cannot be explained by environmental allergens.
Unfortunately, the only proven method for diagnosing food allergies continues to be dietary restriction trials lasting at least 8 to 10 weeks. Therefore, in most cases, a diagnosis of CAD is first ruled out or confirmed before moving to include food allergy as a potential cause.
ICADA Recommended Treatments
The committee makes a distinction between treating acute flares of CAD and treating/managing chronic cases of CAD. An acute flare refers to the sudden onset of clinical signs, usually in a localized region of the body, in a dog who has either not been previously diagnosed or who had been diagnosed but whose symptoms were well managed.
Chronic CAD is identified as long-term cases that have either remained undiagnosed or have not been treated successfully. Chronic cases are characterized by widespread skin involvement, self-induced lesions, infection, skin changes, and severe and prolonged discomfort in the dog.
The primary goal in treating both acute flares and chronic cases of CAD is to stop the itch. This is of vital importance because it is the itch-scratch cycle that leads to self-induced trauma, unrelenting inflammation, and infection. Stopping the itch not only makes the dog feel better (consider how we feel when we have poison ivy and are able to relieve the itch), but also breaks the itch-scratch cycle and allows the skin to heal. Long-term management approaches of CAD include limiting the dog’s exposure to allergens (if they are known) and preventing the recurrences of flares.
The ICADA emphasizes that therapy for the atopic dog must always be approached on an individual basis and will usually be multimodal. This means that it will include various combinations of topical or oral anti-pruritic medications, control of secondary infections and parasites, allergen avoidance when possible, and in some cases, allergy hyposensitization (“allergy shots”). The current ICADA guidelines identify a variety of oral (systemic) and topical medications along with several management approaches that have been demonstrated through research to be effective:
Improved Skin Hygiene and Care – Frequent bathing with a non-irritating shampoo physically removes allergens from the body, cleanses the skin, and may reduce bacterial colonization (growth). One study showed that using a lipid-containing antiseptic shampoo reduced pruritus in dogs with CAD and that the benefit was enhanced when the dog was bathed in a whirlpool.
However, bathing the dog using the whirlpool alone (without the shampoo) also reduced itchiness, suggesting that the complete elimination of allergens and thorough cleansing of skin was more important than the type of shampoo that was used. ICADA states that there is currently no evidence supporting the benefit of any specific type of shampoo ingredient, such as oatmeal, antihistamine, or glucocorticoids. The bottom line is that frequent bathing (or perhaps swimming?) may be one of the most important therapeutic approaches for atopic dogs.
Identification and Avoidance of Flare Factors – Because dogs may be allergic to more than one allergen in the environment (or in food), flare factors are considered to be anything that causes a sudden return of symptoms in a dog. For example, the implementation of an effective flea-control program will remove flea-associated dermatitis as a potential flare factor.
Because house dust mites are considered to be the most important source of allergens in dogs with CAD, measures for controlling these mites in the home may be effective (though, admittedly, difficult to accomplish). Additionally, as stated previously, the ICADA recommends an elimination food trial for those dogs who have suspected food allergy.
Without question it is difficult (if not impossible) to prevent a dog’s exposure to many types of environmental allergens. Therefore, as much as it would be nice to say that simply bathing and reducing exposure to allergens will do the trick, most dogs with CAD will also require some form of medical therapy.
Topical Medications – A wide variety of topical sprays and spot-on treatments are promoted and sold as aids for reducing itching and supporting skin healing in dogs. However, of the many ingredients that are found in these products, only two are supported with scientific evidence.
The strongest evidence is for spray-on medium-potency glucocorticoid sprays. Three randomized, controlled research trials showed that two brands of these sprays, Genesis® and Cortavance®, both produced by Virbac, effectively reduced pruritus and self-induced skin damage in dogs. The ICADA recommends the use of these sprays (or similar products) primarily during flares on a localized region such as the dog’s belly or feet.
Because long-term application of even low concentrations of glucocorticoids can lead to skin thinning and other skin problems, these sprays should never be used in chronic cases and should be limited to a short period of time (less than two months).
There is one study showing that a topical immune-modulating ointment called tacrolimus (Protopic®, Astellas Pharma) reduced signs of CAD when used for several weeks. Tacrolimus may be helpful in healing skin in chronic cases as it does not have the long-term side effects on skin that are associated with topical glucocorticoids.
Oral Medications – When a dog is chronically affected or when symptoms cannot be controlled using hygiene and topical medications, a short course of systemic oral medications may be required. The two types of oral medications that have the strongest evidence for efficacy are the oral glucocorticoids and cyclosporine. The most commonly used glucocorticoids in dogs are prednisone, prednisolone, and methylprednisolone.
A major difference between glucocorticoids and cyclosporine is that a reduction in pruritus (itchiness) occurs much more rapidly, often within 24 hours with glucocorticoids, while treatment for 4 to 6 weeks is required before clinical benefit is seen with cyclosporine (Atopica®, Novartis).
In both types of drugs, a higher loading dose is used initially to control signs. The prescription is then gradually reduced to the lowest effective dosage. This helps to prevent the side effects associated with glucocorticoids (increased appetite, drinking, and urination and increased risk of urinary tract infection). Although reported at a low rate, side effects of cyclosporine include nausea and vomiting. (Note: When a dog has a concurrent bacterial skin infection, oral glucocorticoid therapy is not recommended prior to treating the infection).
Although some owners (and veterinarians) are resistant to using glucocorticoid therapy because of its long-term risks, the ICADA supports their use – for as short a period as possible and at the lowest effective dose. Similarly, although there are fewer documented side effects with cyclosporine, its use may be cost-prohibitive for some owners. It should be noted that these drugs are recommended only when signs are too severe or too extensive to be controlled with frequent bathing and topical formulations.
The ICADA also recommends medications that may have a steroid-sparing effect be investigated. These are adjunctive (supporting) therapies that, when added to a treatment regimen, may allow lower dosages of glucocorticoids or cyclosporine.
Between 2010 and 2015, one new oral medication was tested using a series of clinical trials and was approved for use as an antipruritic (anti-itching) drug in dogs. It is a drug called oclacitinib, marketed by Zoetis under the trade name Apoquel®. Oclacitinib is in a class of drugs known as the Janus kinase inhibitors (JAKs). It has a different mode of action than other anti-inflammatory agents such as prednisone and cyclosporine, and functions to inhibit the neuronal itch sensation – the nervous system component of the itch-scratch cycle discussed above.
The benefits of oclacitinib include a very rapid reduction in pruritus, with dogs showing reduced itchiness within four hours of the initial dose. A series of trials comparing Apoquel to glucocorticoids and cyclosporine reported equal or better effectiveness with the new drug when used to treat dogs with CAD.
Anti-microbial therapy – Antimicrobial therapy is only needed in dogs who have concurrent skin and/or ear infections that have developed as a result of CAD. While these infections can develop during flares, they are most commonly seen in dogs who are chronically affected. The two most common microorganisms that are involved are Staphylococcus bacteria and Malassezia yeast.
Similar to its recommendations for anti-inflammatories, the ICADA recommends using topical anti-microbial agents for infections whenever possible. Oral (systemic) antibiotics and anti-fungal drugs should be used only when needed to control recurrent or severe infections.
Allergen-Specific Immuno-therapy (ASIT) – Better known among dog owners as “allergy shots,” ASIT refers to the practice of administering low and gradually increasing concentrations of an allergen extract subcutaneously.
Intradermal or serology testing is first used to identify the specific agents (allergens) to which the dog reacts. Once identified, the specific environmental (note: NOT food) allergens to which the dog reacts are used in the immunotherapy regimen.
ASIT is not universally effective; studies report that between 50 and 80 percent of treated dogs show improvement of signs over a 6- to 12- month period. Because ASIT is time-consuming and expensive, the ICADA recommends it when other anti-inflammatory treatments have been unsuccessful or when other treatments are associated with unacceptable or severe side effects in an individual.
What the ICADA Does Not Recommend
The ICADA has a strong consensus that the diagnosis of atopy in dogs is a clinical diagnosis, based upon the dog’s signalment (breed, age, living situation), clinical signs, and disease history. The committee emphasizes that neither serological (blood) nor intradermal (skin) testing is reliable as a tool for diagnosing CAD because of these tests’ high risk of false positive results. However, following a diagnosis, these tests may have some use in identifying flare factors for allergen-avoidance management or if immunotherapy is being considered. However, as attractive as it may sound to dog owners, CAD (just like food allergy) cannot be successfully diagnosed through a simple blood or skin test.
There are also several proposed treatments for CAD that do not have sufficient evidence to support them and are not recommended. Perhaps the most important of these, when one considers the popularity of their use with itchy dogs, are the type-1 antihistamines. Examples of these are hydroxyzine, diphenhydramine (Benadryl), clemastine (Tavist), and chlorpheniramine.
When examined as a group, there is no conclusive evidence that these drugs are effective for either acute flares or chronic cases of CAD. There is some evidence of a very moderate prednisone-sparing effect when trimeprazine was administered to dogs with CAD. However, because antihistamines also have a sedating effect in dogs, it is possible that the sedating effect was responsible for the small benefit that was reported in that study. While it is possible that antihistamines may be helpful to prevent recurrence when administered daily after an atopic dog’s signs have been controlled, studies are still needed to test (and support) this hypothesis.
The ICADA also reports that increasing a dog’s essential fatty acid (both omega-6 and omega-3 classes) intake through either supplementation or by feeding an EFA-enriched diet is unlikely to provide measureable benefit to dogs with CAD when used alone. There is evidence that increasing EFAs in a dog’s diet can improve coat quality and reduce dry skin (aid in skin hydration). However, there is no evidence that supports the use of any particular combination of EFAs, dosage, or ratio of omega-6 to omega-3 fatty acids.
A single study reported that increasing EFAs in the diet using a Chinese herbal supplement (Phytopica, Intervet-Schering Plough Animal Health) had a glucocorticoid-sparing effect in some dogs with CAD. However, no other product has been shown to be effective, so the ICADA could not make a recommendation for the use of essential fatty acids in general.
Similarly, the ICADA reports note that there is insufficient evidence to support the use of topical formulations that contain essential fatty acids, essential oils, or complex lipid mixtures to benefit dogs with CAD.
The Bottom Line
Happily for owners of dogs with CAD, it seems that one of the most highly recommended practices to prevent flares and reduce the itchiness in our dogs is the simple practice of frequently rinsing off our dog’s coats (and any adhering allergens) through weekly baths using a mild and non-irritating soap (or, perhaps, a nice swim in the pool).
Reducing a dog’s exposure to flare factors such as fleas, an identified food allergen (when present), and environmental pollens is also key. Treating flares with topical anti-inflammatory and antimicrobial agents is similarly recommended.
When topical treatment is not effective or when dogs are chronically affected, veterinarians and owners have several medications to choose from for systemic therapy. In all cases, the ICADA emphasizes that treatment for CAD is “multimodal,” involving a variety of possible approaches that meet the needs of the individual patient and owner, with the primary objectives of reducing itchiness, maintaining a healthy skin and coat and supporting the dog’s long-term health and well-being.
As for my dogs, I hope that we continue to see the anti-itch benefits of our pool that go beyond enjoying swimming, dock diving, and retrieving!
Linda P. Case, MS, is the owner of AutumnGold Consulting and Dog Training Center in Mahomet, IL, and author of Dog Food Logic and other books on nutrition for dogs and cats.