Giant Cell Arteritis (GCA)
https://www.mayoclinic.org/diseases-conditions/giant-cell-arteritis/symptoms-causes/syc-20372758#:~:text=Giant%20cell%20arteritis%20causes%20inflammation,and%20go%2C%20or%20subside%20temporarily.
GCA and PMR are "associated" but that doesn't mean they are the same.

PMR doesn't always "progress" to GCA especially when PMR is treated. The association between the two is people can have PMR only or GCA only and approximately 20% of people have both PMR and GCA.

"The percentage of patients with PMR who experience GCA at some point varies widely in reported series, ranging from roughly 5 to 30 percent."
https://www.uptodate.com/contents/clinical-manifestations-and-diagnosis-of-polymyalgia-rheumatica#:~:text=Association%20with%20GCA%20%E2%80%94%20PMR%20is,1%2C11%2C12%5D.