I don’t know, but it could be totally unrelated to your RA. Several years ago I fell and tore my rotator cuff. Several months after the surgery my opposite shoulder started to really give me pain. It was bad. My orthopedic and physical therapist said it was from over compensating with that arm, since I was either unable or limited in using my injured arm for so long. I think this is a pretty common problem with shoulder / arm surgeries. When I was finally able to start using my dominant arm again, the pain slowly ( very slowly) started getting better. Now, my uninjured arm no longer hurts.

You are so right. RA does that. What you have going on one side can follow the other side in the same place. Just a characteristic of the disease. Maybe check with your Rheumatologist about having you shoulder injected with cortisone or whatever. I had one shoulder freeze and a week later the other froze.(tendonitis) The injections fixed me up in 2 days.

Thanks all for your replies. Things have moved on somewhat.
Thankfully, the pain in both my shoulders has started to improve, unfortunately it has now moved into my hands. First my left hand and now my right hand. RA sure knows how to bully us.

I found this happened with my knees. I potentially tore the meniscus in my left knee about six months ago - it became swollen and painful and was very hard to walk. About a month later, my right knee began to feel similar (I believe it was the swelling), and my mind was completely boggled because I knew I couldn't have the same injury in both knees. I thought perhaps I was overcompensating for my left knee somehow, but the swelling and pain in my right knee became almost worse than the left. I was diagnosed approximately three months ago with RA.

All I know is that I had both shoulders operated on in the last 4 years and did get pain relief following these surgeries. Shoulders are fine, but now have been diagnosed with RA in both hands, neck and right toe. I think maybe, I have had RA for many years but never was diagnosed. Who knows.