Atopic dermatitis

What it is

Canine atopic dermatitis (CAD) is a hereditary, inflammatory and pruritic skin disease with characteristic clinical features, most often associated with IgE antibodies against environmental allergens such as house dust mites and pollens. A defective epidermal barrier lets allergens and microbes penetrate the skin more easily, and an abnormal immune response then drives inflammation and itch. When the same clinical picture is caused by food allergens it is called food-induced atopic dermatitis. Secondary infections with Staphylococcus pseudintermedius and Malassezia pachydermatis are very common and worsen the itch.

Who it affects

Signs usually start between 6 months and 3 years of age. Many breeds are predisposed, among them the West Highland white terrier, Labrador and golden retriever, French bulldog, boxer, shar-pei, German shepherd and several terriers. Signs may be seasonal at first and become year-round.

Anatomy involved

The disease affects the skin (cutis), especially the epidermis and the superficial dermis. Its distribution is typical: face (around the eyes and lips), concave surface of the pinnae, ventral neck, axillae, inguinal region and ventral abdomen, flexor surfaces of the elbow and tarsus, paws (dorsal and interdigital) and perineum. The dorsal lumbosacral area is usually spared, which helps to distinguish it from flea allergy dermatitis.

Clinical signs

Pruritus is the cardinal sign: licking, scratching, chewing, rubbing the face. Primary lesions are erythema and sometimes papules; chronic self-trauma leads to alopecia, excoriations, lichenification and hyperpigmentation. Recurrent otitis externa, pododermatitis, superficial pyoderma and Malassezia dermatitis are common.

Diagnosis

The diagnosis is clinical and by exclusion; there is no single confirmatory test.

• Compatible history and distribution of lesions (clinical criteria such as Favrot's help).
• Rule out ectoparasites (fleas, Sarcoptes, Demodex) with strict parasite control and skin scrapings.
• Cytology to detect and treat secondary bacterial and yeast infections.
• Elimination diet with a novel or hydrolysed protein for about 8 weeks, followed by challenge, to identify food-induced disease.
• Intradermal or serum allergen-specific IgE tests do not diagnose the disease; they are used once the diagnosis is made to select allergens for immunotherapy.

Treatment

Management is multimodal and lifelong: avoidance of identified allergens where possible, strict flea control, treatment of secondary infections, bathing and support of the skin barrier (essential fatty acids, emollients). Itch and inflammation are controlled with glucocorticoids, oclacitinib, lokivetmab or ciclosporin, chosen according to whether the flare is acute or chronic. Allergen-specific immunotherapy is the only treatment that can change the course of the disease. Owners should understand that the goal is control, not cure.