Hi XXXXXXXXX, let me see if I can help.
Discoid lupus or lupus erythematosus is one the the most common auto-immune diseases of the skin. Treatment is usually prednisone or a topical steroid, vitamin E and the goal, after the skin is normal, is to move from steroids to tetracycline and niacinamide.
A great article can be found at www.petplace.com and enter discoid lupus in the search box.
I'm not aware of the use of vitamin D in this disease, but the dose of vitamin E is 5 to 10 units per pound twice daily.
Hope this was helpful and sorry about the wait.
Dog Veterinarian
30 years in private practice, 2008 WA State Vet of the Year