Are you an orthopedic surgeon?

I had PMR and other problems including spinal stenosis. I'm in need of a lumbar fusion sometime in the future. I noticed an increase in lower back pain whenever I had PMR flare ups.

I don't think chronic inflammation discriminates based on a diagnosis. The inflammatory responses of a deranged immune system can attack anywhere it pleases. The immune system inflammatory responses aren't always logical. I would be inclined to believe you have something more than PMR going on as @johnbishop suggests.

I have inflammatory arthritis in addition to PMR. Damage to my spine was a late finding on an MRI long after I was diagnosed. There was little evidence of inflammatory arthritis at the time and diagnosis. Inflammatory arthritis was suspected based on symptoms and labs but almost no radiographic evidence. I don't know what an MRI or PET scan would have showed when I was diagnosed.

I had advanced degenerative arthritis of my right knee as a result of a meniscectomy when I was a teen. My right knee would hurt whenever I had a PMR flare too.

I had trigeminal neuralgia diagnosed shortly after inflammatory arthritis was diagnosed. Trigeminal neuralgia became a huge problem after PMR was diagnosed. Whenever I had flares of PMR, the electric shocks from trigeminal neuralgia increased to extent that trigeminal neuralgia served as my systemic inflammation alarm.

An extensive work-up was done to find the cause of trigeminal neuralgia. Nothing was found until and MRI "suggested" a problem. The problem the MRI showed was subject to interpretation. The surgeon didn't find what the MRI suggested and how the MRI was interpreted.