CRP and Sacroiliac arthritis: The patient must have radiographic evidence of sacroiliitis, either an increased C-reactive protein (CRP) or magnetic resonance imaging (MRI) evidence of active sacroiliitis and a high disease activity as measured by the Ankylosing Spondylitis Disease Activity Score (ASDAS) and Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), despite the use of at least two different NSAIDs at their maximal dose, for at least 4 weeks in total.