I have a foster who has been with me for some time now. He came to me from another foster home and vet who had misdiagnosed him with cushings. He really did look cushanoid, but his labs were normal and my vet suspected that it was not cushings. We did do the ACTH stim test, but also did skin biopsies and found that he had Alopecia X which is also known as Pseudo Cushings. Here is a thread about him and also before and after pics are throughout that thread.
He was put on Melatonin for his hair loss and it worked! He still has sort of thin hair, but his body is covered with hair. He takes it twice/day and we decided to keep him on it for the rest of his life. I had read somewhere that if the Melatonin works and the pup is then taken off of it and looses hair again, it may not work the next time. Best to leave it be!
http://www.yorkietalk.com/forums/yor...-yourself.html
Hope you get to the bottom of what is going on...not having a diagnosis for something is very frustrating.