When I've read about your cat I'd immediately thought of Julius the BestFriends cat at the TLC club, you'll find more information about him here:
http://www.bestfriends.com/sanctuary/tlcfrm.htm

Just click on the link on the left side headline that says "The world according to Julius...."

Maybe it's the same with your cat...I would ask a second vet for another opinion...
BTW Julius lives a happy life!!! He's just a bit different...