Autoimmune skin diseases in dogs

Clinical symptoms

Dogs with autoimmune skin diseases may exhibit persistent itching, scratching, lesions, wounds, blisters, skin damage, and loss of skin pigment. Two common conditions are Discoid lupus erythematosus (DLE) and Pemphigus. DLE can progress to Systemic Lupus Erythematosus (SLE). The initial stage of DLE involves loss of skin pigment, reddening of the skin, and sores on the nose.

Erosion, ulceration, and injury to the nasal palate may occur, along with damage to the nostrils and tissue around the eyes and ears. Chronic, severe cases often result in visual scar tissue. Most symptoms arise after the outer epidermis and inner dermis are affected, causing the skin layers to separate and leading to painful lesions and pustules. The compromised skin barrier increases the risk of secondary bacterial infections.

Another autoimmune skin disease, vitiligo, damages melanocytes in the skin, lips, and oral cavity. Vitiligo also occurs in cats, horses, and humans. Other autoimmune diseases targeting melanocytes include Vogt-Koyanagi-Harada (VKH) syndrome, which affects the eyes and involves uveitis, acute iridocyclitis, choroiditis, and retinal detachment, and Uveodermatological (UDS) syndrome.

Disease incidence process

The immune system normally eliminates foreign substances through T-cell differentiation, where mature T-cells target foreign antigens. Two tolerance mechanisms exist: positive selection by the thymus selects T-cells that recognize peptides in the Histocompatibility Complex (MHC), and negative selection removes T-cells that recognize self-antigens with high affinity via apoptosis. Incidence of autoimmune skin diseases varies by breed, age, sex, genetics, and environmental factors.

For vitiligo, certain breeds have a higher genetic risk, including Rottweilers, German Shepherds, Old English Sheepdogs, Doberman Pinchers, Dachshunds, and German Shorthaired Pointers, though the exact prevalence is unknown and likely under-reported. Breeds documented with VKH syndrome include Akitas, Samoyeds, Irish Setters, Golden Retrievers, Saint Bernards, Australian Sheepdogs, and Shetland Sheepdogs. Pemphigus vulgaris can occur in any breed regardless of sex or age, but appears more often in male dogs than females, differing from humans where women are more affected. The disease typically begins when the dog is at least five to seven years old, correlating with middle age in humans.

Diagnosis

Because many autoimmune skin diseases share similar symptoms and often affect the oral cavity, a biopsy is usually required for correct diagnosis. A single symptom is unlikely to lead to a diagnosis; instead, biopsy results combined with the canine's history, clinical signs, breed predisposition, and age help confirm the disease. Common symptoms that may lead to diagnosis include alopecia, crusting, ulcerations, and vasculitis. Histopathology evaluations involve extracting affected skin areas, such as lesions, pustules, and crustation sites, and examining tissue samples under a microscope.

Additional tests like antinuclear antibody (ANA) tests and complete blood count with white blood cell differential can provide further information. For Pemphigus vulgaris, Nikolsky's sign—applying pressure along the edge of a blister to see if the skin separates further—can aid diagnosis. However, definitive diagnosis requires biopsies from the blister edge, analyzed using direct immunofluorescence technique and microscopy, as indirect immunofluorescence may yield inaccurate results before the disease has progressed sufficiently.

Treatment

Early treatment is imperative for most autoimmune skin diseases, as progression can lead to severe complications and death. Treatment often involves immunosuppressants such as glucocorticoids, which suppress the immune system's attack on healthy cells by inhibiting calcineurin, an enzyme that controls T-cell production.

For Pemphigus vulgaris, initial treatment typically includes oral prednisone at 1.5 to 13.3 milligrams per kilogram of the dog's weight until symptoms subside, after which the dose is lowered and other medications are introduced. The condition cannot be cured, so the dog requires lifelong immunosuppressants and steroids, commonly cyclophosphamide, methotrexate, or azathioprine. Antibiotics may also be used to reduce infection risk.