Hair loss on the tail alone is not necessarily a sign of adrenal disease.
Ferrets can lose fur on their tails for other reasons, such as blackheads.
From what I've read on this list in the past, bilateral hair loss is a
strong indicator of adrenal disease only when it occurs on the body in
front of the tail.  Speaking for myself, I wouldn't risk putting a ferret
through surgery without better evidence.  Can someone else here please help
with more information?
[Posted in FML issue 2937]