Ankylosing spondylitis (AS), also known as radiographic axial spondyloarthritis, is the advanced disease stage of axial spondyloarthritis (axSpA) [1]. It was characterized by enthesitis involving the spine, inflammation of sacroiliac joints, and inflammatory low back pain, leading to functional impairment, irreversible structural damage and loss of quality of life and work productivity [2]. The prevalence of AS is about 0.5% worldwide and is more common in men [1,3]. Therapy options for AS are limited because conventional synthetic disease modifying antirheumatic drugs(cDMARDs) routinely used for RA are not effective in alleviating axial symptoms of AS [1].
