This isn't a recommendation of anyone in particular but this place has several rheumatologists to choose from. As it says in the following link:

"Fortunately, the last several decades of scientific advancements have brought about a new era in rheumatology. Key discoveries in basic sciences have led to breakthrough drug development allowing us to offer patients novel therapies for immune conditions, which had previously been very difficult to treat."
https://www.ohsu.edu/arthritis-and-rheumatology/division-arthritis-and-rheumatic-diseases
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Considering you have been on Prednisone for a very long time and you can't taper off Prednisone, a rheumatologist at a University Medical Center might have some fresh ideas. I was officially diagnosed with PMR in 2008. I went to the University Hospital in my State. When I was offered a novel therapy, it took me a year to taper off Prednisone. My medical records now refer to a "History of decades of prednisone use but currently off prednisone for the past 4 years."