Lady was recently diagnosed with Cushings. Her's is from taking steroids for a few years for arthritis and is hopefully reversible.
Did your vet do an ACTH stimulation test or a low-dose dexamethasone suppression test? Cushings can be hard to diagnose and those are the two most reliable tests.
Here is some information about those tests:
http://www.marvistavet.com/html/conf...cushing_s.html