Objectives To investigate the longitudinal relationship between inflammatory lesions in sacroiliac joints on MRI (MRI-SI) and clinical disease activity measures (DA) in patients with axial spondyloarthritis (axSpA).

Methods Two-year follow-up data from 167 patients (50% males, mean (SD) age 33 (9) years) fulfilling the Assessment of SpondyloArthritis international Society axSpA criteria in the DEvenir des Spondylarthopathies Indifférenciées Récentes cohort with MRI-SI at baseline, 1 year and 2 years were analysed. The relationship between MRI-SI (as dependent variable) and DA (Ankylosing Spondylitis Disease Activity Score (ASDAS), Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), patient's global DA, night pain, C reactive protein and erythrocyte sedimentation rate, as independent variables) was investigated using two types of generalised estimating equations (GEE) models: model of absolute scores and model of change scores.

Results In the model of absolute scores, the relationship between DA and MRI-SI was different for males and females: in males, but not in females, a statistically significant relationship with MRI-SI was found for all DA except BASDAI. In the model of changes, only ASDAS (beta (95% CI): 2.79 (0.85 to 4.73) and pain at night (0.97 (0.04 to 1.90)) were significantly associated in males while again in females no significant relationship was found. ASDAS fitted the data best.

Conclusions In male patients, but not in female patients, with axSpA, clinical DA, especially if measured by ASDAS, is longitudinally associated with MRI-SI inflammatory lesions.