Everyone has told me that while Cushings is not curable, it is controllable. From what I know, once you find the proper medication, and have the disease managed, something else, such as old age will be the culprit in taking your pet from you.
As I said my Amanda has had Cushings for about 7 years. She takes Lysodrene and prednisone twice a week. She is 16, and while she is a real fighter, she does have her occasional bad days, but I think that is more from the fact that she is 16, than from the Cushings. Another problem I have now is my vet is looking to see what other medication he can put her on because the prednisone, (a steriod which she has been on for 7 years) is probably starting to be as much of a problem as the Cushings.
Take heart. Your dog can live a long time with Cushings. The key is finding a good vet that understands the disease. In the beginning, it can be expensive with all the testing, but I don't know, I think they have probably made real advances in diagnosis and things since my Amanda's Cushing was first discovered. I also think maybe more vets know more about the disease.
I'm not a vet, just a mother to all my animals: I don't know about
the 15 year old you lost last year (I am sorry), I personally think while
Cushings may have been a contributing factor, old age played a bigger part.
But if you vet does not give you a good prognosis and hope on a 10 year old
just diagnosed, find a new vet. Check for an internal specialist or
veterinary school/university near year.