Based on your description of polymylagia rheumatica (I know nothing about it and haven't ever heard of it) and if you happen to be on an interferon, I'm curious if your doctor considered whether or not it might be a side effect of the interferon.
Here's a link
to an abstract about arthritis and bursitis as a side effect of interferons.
cases of two female patients diagnosed with relapsing-remitting multiple sclerosis (RRMS) who developed inflammatory musculoskeletal manifestations, following IFN-beta therapy....resolved with discontinuation of the medication
The role of IFN-beta in inflammatory musculoskeletal disease is unclear.
I'd learned about this some time ago as I'm on Avonex and it just seemed like it might be a remote possibility in your situation.