My partner, who was diagnosed at 13 with systemic lupus erythematosis, has been on prednisone for almost 32 years now. The amount she takes goes up and down depending upon whether she's having a "flare" or not. A bone-density test a year or so ago indicated that she has suffered a bit of bone loss and was put on Fosamax. She takes a couple of extra-strength Tums a day as well. We're pretty sure her body has been affected in other ways, but you do what you can, and it's helped her stay alive. Right now, she takes 5mg and 15mg on alternate days. There are fewer side effects that way than if she were to take 10mg a day. It would be even better if she could take all of a dose on one day and nothing on the alternate day, but that's not very effective right now for her.
Long-term can be very "long"-term indeed with some patients.
Sandy