Atopic dermatitis (AD) in dogs and cats

Atopic dermatitis (AD) in dogs and cats

Atopic dermatitis (AD) is a genetically determined, chronic, recurrent inflammatory skin disease, accompanied by pruritus. It belongs to incurable diseases.
Atopy is a hypersensitivity reaction that results in the production of IgE class antibodies against environmental allergens.

Why do only the ‘chosen few’ get ill?

The answer is hidden in the name. The word atopy is derived from the Greek word atopos – meaning unusual, out of place. Why unusual? Because (fortunately) only some individuals are prone to an abnormal (because excessive) response to allergens commonly found in the environment, e.g. house dust mites, pollen. This contact results in the activation of inflammatory cells and the production of inflammatory mediators, i.e. the substances responsible for the development of pruritus.

Why does this happen?
Let’s start at the beginning…

The skin is a miracle coat. It protects the body from excessive water loss and the entry of pathogens from the external environment.
It has its own ‘private’ immune system (SIS).
In the case of atopics, there is ‘damage to the mantle’ as a result of faulty epidermal structure. An inadequate amount of lipid complexes: cholesterol, fatty acids and ceramides, as well as disturbed synthesis of stratum corneum proteins (filaggrin) facilitate the penetration of allergens. This is when the SIS “springs into action”. Located in the epidermis, so-called ‘scout’ dendritic cells recognise antigens (i.e. ‘strangers’) and pass the information on. And this is where another defect arises – an excessive (inadequate to the stimulus) reaction on the part of the immune system.
Thus, the decision to ‘sentence’ is the resultant of a malfunctioning epidermal barrier (so-called ectodermal defect) and increased production of IgE class antibodies .

Most common allergens

The most common allergens include:

  • house dust mites (up to 80% of dogs)
  • house dust mites
  • fungi and moulds
  • tree (poplar, oak, birch, willow) and grass pollen

Sensitisation to just one allergen is rare. Usually to a group of allergens.
It is thought that dogs born during the pollen season are more likely to develop AD, which would confirm the suspicion of allergisation during the first months of life.
On the other hand, confining pets to their homes, increases their exposure to house dust allergens, storage mites or our epidermis.
Increasing environmental pollution – the presence of ozone, SO2, NO2 – is also significant.

Symptoms of atopy

The problem of atopy appears in animals between 6 months and 3 years of age. It manifests itself by pruritus with a typical distribution (facial area – skin around the eyes and lips, inner surface of the auricles, lower abdominal area, armpits, groin, interdigital spaces and anus, and the base of the tail on the ventral side).
One of the first and leading symptoms is erythema (i.e. reddening of the skin) and pruritus, accompanied by scratching and rubbing of the animal, so over time hair thinning, secondary bacterial (Staphylococcus intermedius and pseudo-intermedius) and fungal (Malassezia yeast) infections, discolouration and lichenisation of the skin (i.e. thickening of the skin as a result of chronic inflammation) join in.
An inflammation of the external auditory canal is often an accompanying symptom.
It may also be accompanied by conjunctivitis.
Pruritus may be seasonal or year-round (depending on the allergen).
Predisposed breeds include:

  • Golden retrievers
  • Labradors
  • Boxers
  • French bulldogs
  • West highland white
  • terriers
  • ON
  • Setters
  • Schnauzers
  • Spaniels
  • Shar-Pei

Recognition of atopy

The first step in making the diagnosis is to carry out a detailed history, a thorough clinical examination and diagnostics to exclude other diseases associated with pruritus (food allergy, allergic flea dermatitis, dermatophytosis, epitheliotropic lymphoma).
Allergic tests, both serological and intradermal, should be used as an adjunct to clinical diagnosis and not as a basis for making a diagnosis. They are performed in animals over one year of age (e.g. a puppy from a spring litter – tests in the autumn when it is 1.5 years old).
In dogs, an increase in IgE also occurs in the course of parasitic infestations, so the animal should be thoroughly dewormed before allergy testing is carried out.
At least Therefore, before allergy testing, the animal should be thoroughly dewormed. Steroid medication should be discontinued at least 14 days before the test and antihistamines 10 days before.
In the event of a positive allergy test, especially against year-round allergens such as house dust mites, it is possible to carry out desensitisation.
Desensitisation involves administering the allergen in slowly increasing doses. This “tames” the body to the allergen. The desensitisation process takes about three years. A 70% reduction in allergy symptoms is considered a success.

How can we help a pet with atopy?

  1. Avoid factors that trigger or exacerbate symptoms, e.g., complicated infections, environmental allergens
  2. Reduce pruritus:
    steroid therapy applied generally
    topical steroids (in the form of ointments, creams, sprays)
    cyclosporine (“imposter” of the immune system)
    monoclonal antibodies (these are proteins that combine with a substance called interleukin 31 to inhibit itching in AD)
  3. Skin care:
    shampoo therapy + spray (adjunctively to reduce opportunistic flora, which multiply excessively as a result of weakened skin barrier). Properly performed, shampoo therapy plays a key role in reducing the use of general medications.
  4. Administer EFAs (omega – 6 acids responsible for, among other things, maintaining the water barrier, and omega – 3 acids that exhibit anti-inflammatory and anti-edematous effects).

Good to know

Atopy is a chronic and incurable disease, which the doctor should inform the Carer about. Therapy consists of toning down the symptoms in order to make the patient’s life comfortable. The success of the therapy depends to a large extent on good cooperation between the doctor and the Carer and consists in enabling the patient to live in good comfort.

Ilona Blanc, veterinary surgeon, specialist in diseases of dogs and cats

25 August 2021