Atopic Dermatitis

Description

Atopic dermatitis is a heritable disorder in which animals are hypersenstive to common environmental allergens. It is one of the most common skin diseases of dogs worldwide.

Signalment

The typical patient with canine atopic dermatitis has an onset of allergic symptoms between 6 months and 3 years of age. Although possible, it is very uncommon for dogs less than 6 months to exhibit symptoms of atopy. Due to the heritable nature of this condition, breed predispositions occur. These may vary with the area being evaluated (genetic pool), as well as over time since breeders select for certain traits and characteristics. Studies that have evaluated relative risk of developing atopy compared to regional dog populations report the following breeds to be at risk for developing atopy: Beaceron, Boston Terrier, Boxer, Cairn Terrier, Cocker Spaniel, Dalmation, English Bulldog, English Setter, Fox Terrier, Sealyham Terrier, Setters, Sharpei, West Highland White Terrier, Wire Hiared fox Terrier, and Yorkshire Terrier. Breeds with decreased relative risk include the Cocker Spaniel, Dachshund, Doberman Pinscher, German Shepherd, German Short-haired pointer, and Poodles. There does not appear to be a sex predilection for developing atopy.

Certain breds are predisposed to atopic dermatitis. These include West Highland White Terriers, English Setters, Shar-Peis, Wirehaired Fox Terriers, Golden Retrievers, Dalmatians, Boxers, Boston Terriers, Labrador Retrievers, Lhasa Apsos, Scottish Terriers, and Shih Tzus<sup.merck. The age of onset is generally between 6 months and 3 years, and there are no sex predispositions.

Diagnosis

Clinical Signs

Signs are often, but not always, seasonal. Pruritus is the key feature of atopic dermatitis and may be the only complaint. This gives rise to self-trauma, causing lesions. Lesions can include alopecia, erythema, scaling, crusting, excoriations and salivary staining. With time, lichenification, and hyperpigmentation develops. Certain areas of the body are affected more frequently than others: the feet, face, ears, axillae and vental abdomen are predilection sites. Secondary infections such as superficial staphylococcal pyoderma and Malassezia are common. A small number of cases may present only with chronic or recurrent otitis externa.

It makes sense that if the route of allergen contact is through percutaneous absorption, that hairless areas and areas of contact would be most commonly affected. A typical dog with atopic dermatitis will exhibit pruritus of the face (periocular and muzzle area), ears (pinnae and canals), feet, axillae and inguinal region. Dorsal pruritus is uncommon, and may in fact, if present be associated with flea allergic dermatitis which is often seen concurrent with atopic dermatitis.

Affected areas generally exhibit erythema, pruritus, and occasionally have a macular-papular eruption. With time, more chronic changes occur: lichenification, hyperpigmentation,, scaling and seborrhea. Secondary infections are common, with both bacterial pyoderma and malassezia dermatitis affecting the skin and yeast and bacterial otitis. Hyperhidrosis is a common symptom.

Some patients may exhibit symptoms of allergic rhinitis with sneezing, nasal discharge and allergic conjunctivitis. However, this is an uncommon manifestation of atopic disease in dogs.

In dogs pruritus is considered a hallmark of atopic dermatitis and emphasized by feet licking and nose or head rubbing. Since the occurrence of primary cutaneous lesions has never been firmly established, it may be that all the cutaneous changes are secondary to itch-induced scratching. This hypothesis is supported by the finding that although all of the dogs have signs of face rubbing and feet licking, only two-thirds have cutaneous lesions at the muzzle and pedal areas. In mild cases, one may only see broken hairs or salivary discoloration (rust colored) of the hairs. The incidence of a superficial pyoderma and of Malassezia infection is significantly higher in dogs with atopic signs together with immediate skin test reactivity, than in dogs with clinical manifestations but without a positive skin test. Otitis externa is a common finding in atopic dogs (up to 80 per cent) and even in 40 per cent of dogs as the initial problem. The head and legs are involved in 70 - 80%, and the axillaries, the abdomen and/or groins in 40 - 60% of dogs.

Treatment

cyclosporin

References

1. Beale, K M (2006) Atopic Dermatitis: Clinical Signs and Diagnosis. Proceedings of the North American Veterinary Conference 2006.
2. Merck & Co (2008) The Merck Veterianry Manual (Eight Edition), Merial.
3. Willemse, T (2007) The Newest on Canine Atopic Dermatitis. Proceedings of the Southern European Veterinary Conference & Congreso Nacional AVEPA.