Canine Hair loss on bridge of nose

Question
I have a male schnauzer that has lost his hair on the front part of the bridge of his nose.  I don't think there is anything he is rubbing against to cause the hair loss. He does not itch it or it is not irritated. The area is just smooth.  I would like some suggestions on what it could possible be. I plan to take him to the vet but wanted some idea to make sure the proper tests are done.  I have other dogs and do not see any hair loss on them but it may be coming.  Thanks!

Answer
In that area there are a few possibilities.  Sunburn, infection, and trauma are fairly common. We will often use a steroid creme on this area. But there are 2 diseases that need to be ruled out if treatment with topical steroids do not help.  They are pemphigus and discoid lupus.  These are are two immune diseases that affect the top of the nose.  The only way to diagnose these is by skin biopsy.