Esen I, Jiemy WF, van Sleen Y, et al. - In giant cell arteritis (GCA), active vessel inflammation is reflected by increased plasma Pyruvate Kinase M2 levels (PKM2), a glycolytic enzyme. PKM2 levels may aid disease diagnosis as well as disease monitoring in GCA.

• Inflamed (n = 12) and non-inflamed (n = 4) temporal artery biopsies (TABs) from GCA patients and non-GCA (n = 9) patients were used for immunohistochemical detection of PKM2.

• In GCA patients (n = 44), age-matched healthy controls (HC, n = 41), metastatic melanoma patients (n = 7) and infection controls (n = 11), measurements of dimeric PKM2 levels in plasma were obtained.

• In GCA patients, PKM2 was abundantly expressed in TABs.

• GCA patients exhibited increased dimeric PKM2 plasma levels, and correlation of dimeric PKM2 plasma levels with CRP, ESR, calprotectin, and YKL-40 levels was found.

• GC-treatment induced downmodulation of elevated plasma PKM2 levels.

• At the site of vascular inflammation, presence of PKM2 was evident in both macrophages and T cells.

• Correlation was found between circulating PKM2 levels and average TBR (target to background ratios) PET scores.