Discoid lupus is an immune mediated skin disease that is probably related to systemic lupus erythematosus (SLE) but instead of affecting the whole body as SLE does, it primarily affects the nose and face. As far as I know, there is no known cause of this problem but it does seem more frequent in dogs of the German Shepherd, Collie, Brittany Spaniel, Shetland Sheepdog, Siberian Husky and German Shorthaired Pointer breeds.
Initial Signs of Discoid Lupus in Dogs
The disease normally starts as loss of pigment around the nose. There may be scabby sores or just scaling of the nasal tissue. The surface of the nose may change from its typical cobblestoned appearance to a smooth surface. As this disease progresses it can cause deep sores on the borders of the nose where it meets normal skin and the sores start to progress up the bridge of the nose. Some dogs seem to be really bothered by this condition and others show little reaction to the sores.
Prevent a Dog's Exposure to UV Light
Ultraviolet light seems to make the sores worse, so the disease may appear to be seasonal. It is more common in areas in which exposure to ultraviolet light is increased, such as high altitudes. If the depigmentation leads to sunburn, squamous cell carcinoma becomes more likely than in other dogs. Topical sunscreens can be very beneficial, although it is hard to get dogs to leave them on. Keeping the dog in during the peak sunlight hours is probably the most effective way to prevent excessive exposure to UV light.
Treatment depends on the severity of the disease. In many cases, topical treatment will be all that is necessary, using a corticosteroid ointment (Panalog, Synalar and others). It is usually necessary to use a fairly potent corticosteroid. Vitamin E supplementation is sometimes beneficial but can take several months to show much effect. Severe cases require treatment with corticosteroids. It is possible that other immunosuppressive therapy such as gold salts or azathioprine (Immuran) could be beneficial but this is rarely necessary to consider. In people, this condition is often responsive to antimalarial medications but I do not know if this is safe or effective therapy for dogs.