*Structural damage of SIJs on conventional pelvic x-rays defined as grades 2–3 (grades of sacroiliitis in the DESIR cohort are defined as: 0=normal; 1=doubtful; 2=obviously abnormal; 3=fused): this scoring method used by local investigators in DESIR is derived from the modified New York criteria for radiographic sacroiliitic changes with one modification: grades 2 and 3 of the New York criteria were pooled to make a single grade.

†Structural damage of the SIJs on pelvic MRI. Structural damage was defined as the definite presence of characteristic lesions such as sclerosis, erosions, bone bridges and ankylosis. Changes were scored as: 0=normal; 1=doubtful; 2=abnormal. For this analysis, structural damage of SIJs, yes=grade 2.