My yorkie "Baby" had a bald spot when she was four that looked similar only round and about the size of a nickle. My vet told me "it just happens sometimes for no good reason just as people will sometimes get a small bald spot on their head and it will either stay that way, come back normal or come back gray". Baby's hair never came back but she lived to be 16 years old (still miss her terribly) and it never happened in any other spot...
R.I.P. "Baby"
