The first section of this thesis aims to provide an international perspective on the characterisation of patients with axial spondyloarthritis. Through different aspects of the classification criteria, we review the importance of global applicability of these criteria. As classification criteria ensure the same patients are selected for participation in clinical trials worldwide, global applicability would allow for direct comparisons between studies executed in different geographical regions. Likewise, standardised assessment and reporting of results from clinical trials allows for direct comparisons between studies investigating different treatments, or identical treatments in populations from a different ethnicity or background, which is debated in the second part of this thesis. Herein, we describe the process of the development of the core set for axial spondyloarthritis, specifically by updating the domains of the ASAS-OMERACT core set for ankylosing spondylitis. In the final part of this thesis, we discuss health-related quality of life and work and activity impairments in patients with chronic back pain suspected of axial spondyloarthritis. UCB PharmaLUMC / Geneeskund
