Allergic dermatitis in cats

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'Eczema' or allergic dermatitis are general terms to describe a group of skin allergies that may be caused by a multitude of factors in cats. 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.

Differential diagnosis

Typical insect bite allergy and flea allergy dermatitis

 

 

Feline head pruritus secondary to food allergy

 

There are several types of allergy tests performed by veterinary dermatologists. The goal of allergy testing is to identify specific substances that are causing an allergic reaction, so that desensitisation through allergy shots may be attempted.  Most dermatologists use a method of allergy testing known as intradermal skin testing. This involves the injection of very small amounts of pollens (from trees, weeds, and grasses), moulds, and insect extracts into the superficial layers of the skin. The test is administered under a light sedative/analgesic so that the patient (dog, cat, or horse) feels no discomfort. 

Skin testing using allergen injections and then visualised with intravenous flourescein. 

Many non-specialists routinely use blood testing methods. There is a great deal of controversy about the reliability of blood testing, since the organ that is affected (the skin) is not the organ being tested for a reaction. There are several different types of blood tests offered by biomedical companies, which may vary in accuracy of results, and in success rates when allergy shots are based on these results. An important point to understand is that neither blood testing nor intradermal skin testing are useful for identifying allergy to foods. 

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

1) Flea bite allergy 
2) Food allergy
3) 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. 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: 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 colour), head shaking.

Diagnosis

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

Skin scraping
Skin cytology
Complete blood count and biochemical profile
Allergy blood tests 
Intradermal allergy testing (see video clip of how it is done. 444 kb)
Dietary trials

Treatment

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)
Fatty acid supplementation
Dietary management
Antibiotics to treat secondary bacterial skin infections

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.

Prevention
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 mould in the household. Eliminating exposure to certain foods is crucial to effective treatment of food allergy dermatitis.