Here are a couple of links about spondyloarthropathy. I suspect there are PMR people who might be misdiagnosed. Otherwise, having multiple autoimmune problems is more common than people might think.
https://enthesis.info/spondyloarthritis/spondyloarthropathy_and_enthesitis.html
I like the diagram in the above link because all these conditions have overlapping features. The diagnosis can change over time when one characteristic starts to predominate.

The following link is a good overall description of all of the spondyloarthropathies. PMR as many of the same symptoms so getting a correct diagnosis isn't as easy as it would seem.
https://boneandspine.com/seronegative-spondyloarthropathies/
One has to wonder about all the arthritis that surfaces in PMR patients once they get down to lower doses of prednisone. Doctors tend to call it osteoarthritis but who knows?

There is a reason why prednisone isn't recommended for inflammatory arthritis. Prednisone doesn't prevent the damage caused by inflammatory arthritis. The approach is to achieve remission as fast as possible to prevent the damage.

With PMR, the approach is to treat the symptoms and wait for PMR to burn itself out.

I should add that "empiric treatment" is the best approach sometimes. My rheumatologist was aware of this but there wasn't much at the time in the way of biologics to treat reactive arthritis. There still aren't any biologics that are FDA approved as far as I know.

Sulfasalazine was used historically because the empirical evidence suggested it was helpful for cases of spondyloarthropathy. Sulfasalazine was my first medication too when I was diagnosed with reactive arthritis

Funny story about sulfasalazine because after starting it, I had a follow-up visit with my medical doctor after a couple of weeks to see if the pain was improving. I told my medical doctor that he was a "miracle worker" because after my first dose of sulfasalazine, the pain stopped. My medical doctor said sulfasalazine wouldn't have worked that quickly so it must have be a coincidence that the pain stopped. Pain caused by reactive arthritis can stop suddenly for unknown reasons. My pain recurred again but that is another story.

Several years later I was thinking about that day my ophthalmologist was treating my uveitis. Then it occurred to me, at one stage, he gave me a handful of little white pills but didn't say what they were. I do recall him saying the pills would help to decrease the inflammation inside my eye.

I had never taken prednisone before so I had no idea what those little white pills were. I'm almost certain I received my first dose of prednisone that day and didn't even know what it was. It wasn't the sulfasalazine that stopped the pain, it was the prednisone that my opthalmologist gave me. My eye doctor was the miracle worker and not my medical doctor.

About 20 years later and huge amounts of prednisone, my rheumatologist didn't know what to try in order to help me get off prednisone. One day after reviewing my ancient medical records., she said it was documented that I had an "excellent response" to sulfasalazine and she wanted to know what I recalled about it.

I didn't have the heart to tell her what I thought about sulfasalazine. I just said the pain mysteriously stopped suddenly when I was taking sulfasalazine but it was making me nauseous so I stopped sulfasalazine. I didn't say that I believed the prednisone from my ophthalmologist actually stopped the pain.