My ferrets almost completely bald

Question
I have two ferrets and the one in question is about 3 1/2 to 4 years old. This past summer (2007) he began losing his hair on his tail and his back.

I read a lot about the adrenal disease and went and saw a vet about it. He has been getting monthly Leuprolide Injections but now the balding is getting worse. The vet said that he wants to do a blood test to make sure it truly is adrenal disease. The shots should have helped his hair grow back, not lose more.

My question is...what else could it be if the tests come out negative? I don't have a lot of money and so far it's costing me $40 a month and the blood test is about $170. What should I do?

Answer
I would agree with the blood test, Lupron doesn't always work to help the hair regrow and surgery may be the only option.  I want to point out that I am not a vet so I would have to default to your vet here.  get the blood test and surgery if required.  If it isn't adrenal, then something else may come out from the blood work.