Hi @juneh I think it's possible that the pain under your arms is related to your PMR. I didn't have pain under my arms, but the backs of my knees were incredibly stiff, which I never saw mentioned in any article I read on PMR. Now I have shoulder osteoarthritis, tendonitis and rotator cuff issues with pain under my arm. The Physical Therapist said it's because the area is "involved." PMR is a form of vasculitis and restricts blood flow so when it attacks the shoulders, the whole area may be impacted. I find an infrared heating pad soothes the pain.