From the brain structural perspective, the gray matter volume in the left putamen in patients with AS increased significantly and was positively correlated with the duration of AS and total back pain (TBP) scores, whereas it was not correlated with bath ankylosing spondylitis disease activity index (BASDAI) scores, C-reactive protein (CRP), or erythrocyte sedimentation rate (ESR) (Hua et al., 2020). Here, CRP is linked to ankylosing spondylitis.