Has anyone had a yorkshire terrier with symetrical hair thinning problem?

I have a 1 yr. old pure bred yorkshire terrier female. She has been spayed. 2 wks ago I noticed hair thinning around rump and back legs. She has no symptoms of illness. Took her to the vet yesterday and he said she might have alopecia areata. Skin scrapings were done: no parasites. She has no visable skin problem. He may do tests for thyroid or adrenal gland problems or even a skin biopsy to find out exactly what she has. Does anyone have any experience with this health issue in yorkies? Does it go away on it's own? Is there a treatment that is effective?