No differences in serum IL-31 level were observed depending on the presence of radiographic sacroiliitis (mNY-positive (n = 121)14.0 ± 14.7 vs mNY-negative (n = 317) 11.6 ± 14.4; p = 0.09) nor inflammatory sacroiliitis seen on MRI (MRI-SI–positive (n = 195) 12.9 ± 15.6 vs MRI-SI–negative (n = 224) 12.3 ± 15.5; p = 0.58). Here, IL31 is linked to Sacroiliac arthritis.