Allergic Dermatitis in Dogs

Overview of Canine Allergic Dermatitis

Allergic dermatitis is a general term to describe a group of skin allergies that may be caused by a multitude of factors in dogs.

Allergies are immune reactions to a given substance (allergen), which the body recognizes as foreign. These reactions occur following initial exposure to the allergen, with subsequent development of a hypersensitivity that causes itching and inflammation upon future exposures.

The most common classes of allergic dermatitis seen in dogs are:

• Flea bite allergy
• Food allergy
• Atopy – an allergic condition caused by inhaled allergens, or absorption of allergens through the skin

Less common are:

• Drug reactions
• Hormonal allergies
• Bacterial allergies
• Allergies to other parasites (mites, intestinal worms, ticks)
• Contact allergies (due to topical treatments or exposure to fibers, floor polish and detergents)

Atopy and flea bite allergy are usually seen in young adults, whereas food allergy can be seen at any age. There are a number of canine breeds predisposed to the development of atopy. And some animals may be prone to development of certain allergies due to genetic factors. Allergic signs may be seasonal, depending on the cause of the allergy.

What to Watch for

Signs of Allergic Dermatitis in Dogs may include:

• Scratching, licking, chewing or biting the skin, feet and ears.
• Red, raised, scaly areas on the skin
• Bumps, crusts or pus filled vesicles on the skin
• Increased skin pigmentation
• Thickened skin
• Loss of hair
• Salivary staining (brown color)
• Head shaking

Diagnosis of Allergic Dermatitis in Dogs

The specific diagnostic protocol may vary depending on what type of allergy or other skin disease is suspected in your dog. Every diagnostic test listed below may not need to be performed.

• History and physical exam
• Skin scraping
• Skin cytology
• Complete blood count and biochemical profile
• Allergy blood tests
• Intradermal allergy testing
• Dietary trials

Treatment of Allergic Dermatitis in Dogs

The treatment prescribed by your veterinarian will vary with the type of allergy diagnosed. The following list includes the possible treatments that may be required.

• Avoidance of offending allergens when possible
• Anti-itch and/or antibacterial shampoos
• Topical anti-inflammatory or antibacterial drugs
• Antihistamines
• Corticosteroid therapy
• Immunotherapy (allergy vaccines)
• A new drug Oclacitinib (Apoquel) has been effective in some dogs
• Fatty acid supplementation
• Dietary management
• Antibiotics to treat secondary bacterial skin infections

Home Care

Home care is a crucial part of treatment for any dermatologic condition. Careful adherence to your veterinarian’s recommendations regarding oral medications and bathing is very important. Some animals may require bathing several times per week. Additionally, medications are often required even after the clinical signs have resolved.

Preventative Care

Although allergic dermatitis cannot be prevented, limiting exposure to allergens will help alleviate some of the clinical signs. Flea control in the environment is imperative for animals diagnosed with flea allergy dermatitis. Treating the pet alone is not sufficient to control the problem.

Environmental reduction of any known allergens is advised. This may require keeping pets inside when pollen counts are high, avoiding long grass or freshly cut grass, and limiting dust and mold in the household. Eliminating exposure to certain foods is crucial to effective treatment of food allergy dermatitis.

Information In-Depth on Allergic Dermatitis in Dogs

As discussed, there are multiple types of allergies. In addition to different classes of allergy, there are a number of other causes of dermatitis that result in the same clinical signs. The following is a list of possible diagnoses in animals with itchy, red, crusty, scaly skin.

• Flea bite hypersensitivity- Animals with this type of allergy can have severe dermatitis even with a low flea burden. In some cases the fleas are not easily identified on the patient. This usually occurs in 3-6 year old animals. The distribution of skin lesions is predominantly on the back end of the pet.
• Atopy- This condition is also known as allergic inhalant dermatitis. Most patients with this disorder are 1-3 years of age. There are known breed predispositions in dogs. The face, feet and armpits are the areas of the body most commonly affected by atopy. As the disease progresses, the signs may spread to the whole body.
• Food allergy- Animals may develop an allergy to a certain component of their diet. This can occur at any age, and often occurs after an animal has been eating the diet for an extended period of time. In addition to dermatitis, some pets with food allergies will also develop vomiting and diarrhea.
• Drug allergy- Many drugs, especially certain antibiotics, have been shown to cause allergic reactions. The signs may range from scratching and redness, to hives, to severe illness and sloughing of the skin. If a drug allergy is suspected, the drug in question should be discontinued immediately.
• Contact allergy or irritant- Animals can be allergic to fibers in a carpet, finishes on a floor or topical shampoos or medications. Additionally, some substances may cause irritation even in animals that do not have an allergy. The dermatitis is often confined to ventral areas (along the underside of the body) or areas where there is a sparse haircoat.
• Pyoderma- A bacterial skin infection can occur alone, or in conjunction with allergic dermatitis. Many animals develop secondary pyoderma from chewing and licking at their skin. The normal skin has many bacteria, which will colonize an area of inflamed or irritated skin and worsen the clinical signs.
• Yeast infection- Infection with skin yeast can also occur secondary to allergy. Many patients (especially dogs) will have yeast and bacterial ear infections secondary to allergies.
• Scabies- This is an intensely itchy disorder caused by mites. Human family members can contract this as well.
• Cheyletiellosis- This is another type of mite that may cause minimal to severe scratching. Humans may also be infected.
• Pediculosis- Lice infestation

Diagnosis In-depth

A thorough history and physical exam are imperative to making an appropriate diagnosis. The distribution of skin lesions will often allow the clinician to limit the list of differential diagnoses. Some commonly performed tests include:

• Skin scrapes- A surgical blade is used to gently scrape the skin surface to look for various types of mites or mite eggs.
• Skin cytology- Smears of fluid or pus filled vesicles or inflamed skin are helpful to diagnose bacterial and yeast infections.
• Complete blood count and biochemical profile- These tests are not necessary in every case of dermatitis. They evaluate the blood cells and organ function, and may be useful if an underlying systemic disease is suspected. These tests are especially useful if the patient has other signs of illness in addition to the dermatitis.
• Allergy blood tests- These are special tests designed to find out which allergens the animal is responding to. Although they can be useful, the test results are not always reliable.
• Intradermal allergy testing- This involves testing the skin for allergic responses by injecting small amounts of known allergens into pre-determined locations in the skin. This type of testing is generally more reliable than the blood tests, but interpretation can be difficult and false test results may occur if not performed properly. Only a trained dermatologist, or a doctor who does many intradermal allergy tests and is familiar with the test interpretation should perform these. Allergy testing of this sort is usually done in cases of suspected atopy.
• Dietary trials- If an animal is suspected of having a food allergy, special dietary trials are the best way to make the diagnosis. This entails putting the pet on an elimination diet, consisting of a protein source that the animal has not previously eaten. Home-cooked diets or prescription diets can be fed. In order for the trial to be successful, all other foods must be excluded. This includes treats, rawhides, flavored vitamins or flavored heartworm medications, and table food. It may take a number of weeks on the diet before the animal shows any improvement in the dermatitis.

Treatment In-depth

The specific therapy for your dog will depend on what type of allergy is diagnosed, as well as how severe the signs are. A combination approach to therapy is often more successful than any single therapy.

• Avoidance of offending allergens- Whenever a specific allergen can be identified based on diagnostic testing, exposure to the allergen should be minimized as much as possible. In cases of flea allergy, a strict flea control program should be started. This includes treating the animal with products to kill adult fleas as well as insect growth regulators, which inhibit flea larvae. Careful eradication of fleas from the environment is also imperative. As discussed, food allergies require eliminating certain foods from the diet. Animals with atopy may benefit from more frequent cleaning of their home environment to limit dust and molds. Limited exposure to pollens and grasses may also be important.
• Shampoos- Anti-pruritic (anti-itch) shampoos can often provide relief to very itchy patients. Additionally, animals with secondary bacterial or yeast infections may benefit from medicated shampoos with antibacterial and antifungal properties.
• Topical anti-inflammatory ointments may be appropriate in cases with mild, regional skin lesions. Additionally, animals with ear inflammation and secondary infection will often require combination antibacterial/antifungal/anti-inflammatory medications for the ears.
• Antihistamines- This class of drug is available in both over the counter and prescription medications. Although not usually effective as a sole therapy, many animals will benefit from antihistamine use to relieve the itch and inflammation. If one antihistamine does not work, a different one may sometimes be more effective. Common antihistamines used include Benadryl (dephenhydramine), Zyrtec (cetirizine), and Chlor-trimetron (Chlorpheniramine).
• Corticosteroid therapy- Corticosteroids are potent anti-inflammatory drugs that are widely used in veterinary medicine for a variety of reasons. They may be necessary in many cases of allergic dermatitis, and can be very effective in relieving the itch and inflammation associated with atopy and flea allergy. They are generally less effective for treating food allergy. Long term use of corticosteroids can have many negative side effects, so they must be used judiciously, and under strict supervision of a veterinarian.
• Oclacitinib (Apoquel) is a new drug on the market that has been effective in some dogs. Oclacitinib how show to inhibit cytokines that cause inflammatory and itching. Oclacitinib is not considered a corticosteroid or an antihistamine but has effects that can be similar.
• Immunotherapy- Use of allergy vaccines, specifically designed for each individual based on allergy test results, can often be helpful in cases of atopy. They are often used in conjunction with corticosteroids and antihistamines, in an attempt to reduce drug dosages. As many as 60-80% of patients with atopy may have improved clinical signs related to immunotherapy. It may take months to see postive results.
• Another therapy includes use of an immunomodulator drug called cyclosporine A (Atopica®, Novartis). Cyclosporine has properties that fight against inflammation and itching. It is generally started daily and often decreased to every other day or every third or forth day as clinical signs improve. It may take four to eight weeks to see improvement.
• Fatty acid supplementation- Supplementing the diet with fatty acids may reduce the degree of inflammatory response seen in the skin of allergic animals. This treatment is very unlikely to eliminate signs, but can be used together with other treatments.
• Dietary management- Once a diet trial has been conducted, specific diets may be required for the life of the pet. Over time, certain ingredients may be selectively added to the diet one at a time, to test for hypersensitivity to a specific ingredient. Eventually the pet may be able to return to eating his normal diet, but this is unpredictable.
• Antibiotics- Oral antibiotic therapy is often needed due to the prevalence of secondary bacterial skin infections.

Follow-up Care for Dogs with Allergic Dermatitis

Optimal treatment for your dog involves a combination of home and professional veterinary care. Follow-up can be critical, especially if your dog does not rapidly improve. Administer all prescribed medications as directed. Alert your veterinarian if you are having problems treating your pet.

Re-exams by your veterinarian may be required every 2-4 weeks, at least initially, to monitor efficacy of the treatment plan. Once the dermatitis is well controlled, certain drugs may be tapered or discontinued. This decision should only be made by your veterinarian. If signs are seasonal, medication may only be required at certain times of the year. Any flare-ups of dermatitis should be addressed early, as clinical signs may worsen quickly if not treated appropriately.

For patients taking corticosteroids, certain side effects are to be expected; dogs will drink and urinate more than normal, may pant, and may have an increased appetite. Adverse effects of this therapy may also include gastrointestinal upset and even bleeding or ulcer formation. This may manifest as vomiting, diarrhea, dark and tarry stools or general weakness. Any of these adverse effects should be brought to the attention of your veterinarian immediately.