GDF15 and rheumatoid arthritis: It is well known that bone erosion is a predominant pathologic feature in rheumatoid arthritis (RA) and GDF15 can predict the presence of severe disease and bone erosion in RA.[13] Moreover, under hypoxia, osteocytes could secret GDF15 to promote osteoclastogenesis.[9] Compared to patients with RA, it was found that GDF15 levels were lower in SpA.[5,13] In the present study, it was found that GDF15 levels were higher in patients with bone erosion compared to those without bone erosion.