PMR attaque quoi?

I have all the symptoms of PMR but t referral to a rheumatologist is months away. In my reading is often see the PMR causes the immune system to attack the body. What exactly is being attacked? Is it cartilage, tendons, or something else. Any insight would be helpful.
Thank you

PMR attacks the large muscles in the hip/thigh and shoulder areas. The stiffness isnt just caused by the pain but movement actually becomes hard, like trying to open a rusty hinge. The pain can be unbelievable and the best way I can describe mine is that it felt like my muscles were filled with ball bearings. I had a lot of trouble getting diagnosed as the doctor didnt believe me, but i persisted until i got the more sensible practice partner who diagnosed it in about 5 minutes and confirmed it with blood test. Prednisolone is wonderful stuff, I took it as soon as i got the script filled and by the next morning i could do anything.