We rescued Roxy from some Craigslist nut jobs, and she had something that looked similar to that.
We had her allergy tested and a skin scraping done and the vet determined that part of the hair loss was a wheat allergy and the rest of it was a bacterial skin infection called pyoderma. She's on antibiotics now along with Benadryl and has to have baths in special medicated shampoo twice a week, and it seems to be really clearing up. It's now just a patch on the back of her neck that looks VERY similar to the picture you have up there, but it's steadily going away.
It might be something to check into!!!
"The nose of the bulldog has been slanted backwards so he can breathe without letting go." - Winston Churchill
If only we humans were made that way.