I can't find any answers!!!!

About a month ago I noticed a depigmented ring on my side. It is a hollow circle and the skin inside is still tan, but the ring is white. I went to the dermatologist and he had never seen anything like it before. He took some pictures and gave me some cream to try for a couple of weeks. Cream was not successful and I had a biopsy of the site on Monday. I have searched on the internet for anything that resembles my skin issue and still have not found a thing. He was thinking maybe Morphea or Vitiligo, but both dont fit with it being in a perfect circle. By the way it is not ringworm. The skin is healthy. Please help!!!