Atopic Dermatitis in Dogs

Atopic dermatitis or Atopy is a condition in which dogs have an inherited predisposition to allergic skin disease. This is due to a genetic cause and means their immune systems are oversensitive and overreact to certain allergy causing substances – allergens – such as pollens or house dust mites. When exposed to the allergens, the immune cells involved in allergies release compounds such as histamine into the body which causes the dog to itch, known as pruritus.

Atopy develops in young dogs usually between 6 months and 3 years old and is very rare in dogs over 7 years of age. It is estimated that 10-15% of the UK dog population could be affected by atopy and some breeds are particularly susceptible. These breeds include Labradors, Golden Retrievers, West Highland White Terriers, Boxers and Bulldogs but any breed, including crossbreeds can be affected. Atopic dermatitis may be seasonal or non seasonal depending on what allergens your dog is reacting to.

Clinical Signs

Pruritus is the main sign associated with atopic dermatitis. You may notice your dog licking or chewing themselves excessively, rubbing themselves on the floor or furniture or over grooming. These behaviours may lead to patches of hair loss called alopecia. You may also notice red, inflammed skin including in the ears as these are often involved in atopy. Other commonly affected areas of the body include the face, distal limbs ie. feet and the underside of the chest and abdomen and groin.

Long term or recurrent skin disease such as atopic dermatitis can cause chronic changes in the skin and hair coat. You may notice saliva staining from the excessive licking or chewing and the skin itself becomes thickened (lichenified) and dark in colour (hyperpigmented).

Up to 65% cases are complicated by secondary skin infections called pyoderma so you may also see red, raised pustules or crusts in the skin which are indicative of infection.

Diagnosis

A diagnosis of atopic dermatitis will not be made in the first consult. Atopy is not simple to diagnose and can be a long and involved process requiring commitment from both the vet and the owner to reach a definitive diagnosis. It is essentially a diagnosis of exclusion meaning that the other causes of allergic skin disease need to be ruled out before atopic dermatitis can be diagnosed. Once your vet is suspicious of atopic dermatitis, they will need to perform a series of tests to rule out these other causes of allergic skin disease.

• Firstly, your dog will need to be on regular flea treatment to rule out an allergy to fleas as this is a relatively common cause of allergic skin disease. This flea control must be continued regularly as flea infestations will exacerbate atopy.                                                                    

• Any secondary infections will need to be treated as these can make the pruritus worse. This is usually done with a combination of shampoos and a course of oral antibiotics lasting at least 3 weeks.                                                                                                                                       
• The next step is to take some samples of the affected areas of skin and these include skin scrapes, tape strips, coat brushings and hair plucks. These will be examined for mites, yeasts, bacteria and fungi. Blood samples may also be taken to look for the presence of the mite Sarcoptes scabeii which causes intensely pruritic mange. Sometimes swabs will be taken from infected areas of skin to see which bacteria are responsible. Any parasites or diseases detected by the above tests will need to be treated appropriately as they may be the inciting cause of the skin disease or will be complicating the atopic dermatitis.

• The next step is to perform a food trial to see if your dog is reacting to an ingredient in the food. Food allergies are not common but it is important to rule them out before starting treatment for atopic dermatitis. Animals on food trials are fed specifically formulated diets such as Hills z/d or Royal Canin Sensitivity Control for a minimum of 6 weeks. It is very important that they are not fed anything else during the food trial, no treats or tit bits, only the special diet. If the skin disease improved during the food trial then the animal is “challenged” with their original food and if the skin disease recurs then is can be confirmed as a food allergy and a suitable diet can be found.

• If the skin disease doesn’t improve whilst on the Hills z/d, Royal Canin Sensitivity Control or similar then a diagnosis of atopic dermatitis can be made. At this stage it is possible to do skin test on the dog to determine what allergens are causing the reaction. This is done by clipping a patch of hair on the flank and injecting small amounts of the allergens under the skin and comparing the reactions around the injection sites after 15 minutes.

Treatment

Essential Fatty Acids (EFA’s): Essential Fatty Acids are present in supplements such as Efavet (please see Efavet dosing information)  Coatex, Yumega and Gomega and they help to stabilise the skin and improve skin and hair coat quality. They are very beneficial in a wide variety of skin problems including atopy.

Antihistamines: These reduce the histamine which is causing the irritation and can work well in conjunction with EFA’s. They can improve around 25% of dogs. There are no veterinary specific products on the market but human preparations are used.

Steroids: Atopic dermatitis is a steroid responsive disease and oral tablets of steroids such as prednisolone will relieve the pruritus but can have side effects such as increased thirst and appetite in the short term and effects on the liver in the long term.

Immunotherapy: Vaccines can be made according to the results of the skin tests described above. A solution containing small quantities of the allergens that the dog reacts to is injected under the skin and over time modulates the immune response so the body doesn’t overreact to exposure to the allergen. It can take several months to have an effect and can improve up to 60% cases of atopic dermatitis but additional medications may still be needed to completely control the atopy and keep the dog as comfortable as possible.

Immunomodulation: A product called Atopica is available to treat atopic dermatitis and consists of soft capsules containing the drug cyclosporine. Atopica targets the specific cells in the immune system involved in allergies and modifies their response, again aiming to reduce the body’s reaction when exposed to the allergens. Atopica has fewer side effects than steroids as its action is more specifically targeted and doesn’t affect other organ systems as the steroids do. It can sometimes cause temporary vomiting or diarrhoea when treatment is first started but is usually resolved without having to stop the medication. Atopica is initially given daily but the dose can be tapered if the response to treatment is good. Atopica is available in various strengths and the exact dose required by your dog will be decided by your vet.    

Please see the following video on recognising the signs of Atopic Dermatitis in dogs;

009 Atopy in Dogs, Environmental Allergies