Perhaps prednisone is still used because corticosteroids quickly relieved symptoms of PMR and were thought to be "relatively safe" when taken on a short term basis. I know of no other treatment that works as rapidly as prednisone does.

The belief is PMR will "burn itself out" relatively quickly in a year or two. The pain relief benefits of "short term" prednisone use outweigh the risks of side effects. Unfortunately the risk of significant side effects increases when prednisone is used "long term." The risks are directly proportional to dose and duration of treatment.

In summary, prednisone is a "quick fix" but not a good long term solution.

There weren't many alternative treatments available during the corticosteroid era for the treatment of many autoimmune disorders. Now, that has changed for some autoimmune disorders but PMR/GCA has some catching up to do.