Interesting stats published by NIH: "The median duration of therapy was 37.3 months. It was estimated that 40 percent of patients will require therapy longer than four years. Corticosteroids were permanently discontinued in 31 patients after a mean of 23.7 months of therapy. The data support the concept of two patient populations--one with limited disease and another requiring long-term therapy."
There's more at https://pubmed.ncbi.nlm.nih.gov/4036982/
This is from 1985 but PMR is PMR, I believe.