@dadcue
Both are corticosteroids, but they differ in potency, duration, and side-effect profile. Hydrocortisone more closely mimics our natural cortisol and causes less adrenal suppression than prednisone. It also has less effect on bone density. It's not supposed to treat PMR as it should only be used to treat the adrenal insufficiency that can occur with long term prednisone use, and as a means of ending prednisone use. For some people, the bone loss from prednisone use is a serious concern and hydrocortisone would be preferable for them. It's an option that should be considered if bone loss is a concern or if elimination of prednisone is preferred.