Clinical outcomes
In general, axial spondyloarthritis (axSpA) follows a chronic course, requiring regular medical care and monitoring. The outcome of axSpA may vary substantially due to heterogenic presentation. For both research and clinical practice, it is important to have relevant, reliable, validated instruments for measuring outcome, to evaluate patients in a standardized way and capture all disease aspects. The Assessment in SpondyloArthritis international Society has developed core sets and instruments to measure these domains, and recommends only the most important domains being measured with best available methods. This chapter provides an overview of the most important outcomes in axSpA and most commonly used instruments to measure these. Additional measures frequently used but not (yet) included in the core set are addressed, and several sets of response criteria applied in axSpA research described. This chapter also provides guidance in which setting (research versus practice) and with which frequency these measures can be used.