Flares are hard to define for PMR. Most people just take more Prednisone for any uptick in pain and call it a flare. I never liked the "flare" terminology because I was never sure what it was. I would simply describe the pain I had which was all the time. I had more pain some days than other days but there was always some pain. The concept of "no pain" was somewhat foreign to me after I was diagnosed with my first autoimmune condition. PMR wasn't my first.

My rheumatologist never referred to flares either. She just wanted to know how much pain I had and checked my inflammation markers to correlate lab values with my pain. She didn't even refer to my condition as PMR very often. Maybe that was because I had multiple autoimmune conditions. She referred to everything as "systemic inflammation with "chronic pain." Her biggest concern was always how much Prednisone I was taking and tried everything she could think of to see if I could reduce my overall cumulative dose without ever expecting me to taper off completely. Maybe that was why i was on Prednisone for 12 years. before I could taper off. My rheumatologist now says I have "refractory PMR." I'm currently being treated with a long term biologic instead of long term Prednisone.
https://www.the-rheumatologist.org/article/how-to-treat-refractory-polymyalgia-rheumatica/
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Once I had an acute onset of excruciating pain. If that wasn't a flare I don't know what was. I must have taken close to 100 mg of Prednisone in 24 hours. I didn't know what else to do. The pain was in my lower back and radiated down my leg to my foot. The large dose of Prednisone relieved the pain so I was thinking it was a flare. I ended up getting an MRI which showed that I had severe spinal stenosis. My rheumatologist said I shouldn't have taken such a large dose of Prednisone. She would have recommended a localized steroid injection instead of systemic oral Prednisone.