You've used the word "devastating" twice in this thread in regard to ypur diagnoses. I suggest that, as much as possible, you remind yourself that diagnoses are just labels and the truth is that the labelers are not making the statin connection (that you know is there) and they are using words like "undifferentiated" which simply mean they don't know much. What really counts is not their questionable labels but their management of your symptoms. Try whatever treatments may make some sense, but don't let the doctors get you down with their labels. If the doctors are not offering therapies, they're not worth the copayments and certainly not worth the frustration.
As for any "progression", try to cross that bridge when and if you come to it -- not now. Truth be known, I'd trade my statin damage for RA any day. My wife has RA. It's no picnic, but there are good treatments available for RA and the progression is predictable and largely haltable with treatments like Remicade, Humira, etc.
Hang in there.