Objective To assess the progression of radiographic sacroiliitis in a cohort of patients with early axial spondyloarthritis over a period of 2 years and to explore predictors of progression.

Methods 210 patients with axial spondyloarthritis from the German Spondyloarthritis Inception Cohort have been selected for this analysis based on availability of radiographs at baseline and after 2 years of follow-up. Radiographs were centrally digitised and the sacroiliac joints were scored independently according to the grading system of the modified New York criteria for ankylosing spondylitis (AS) by two trained readers. The readers scored both time points simultaneously but were blinded for the time point and for all clinical data.

Results 115 patients (54.8%) fulfilled the modified New York criteria for AS in their radiographic part in the opinion of both readers at baseline, while 95 patients (45.2%) were classified as non-radiographic axial spondyloarthritis. More patients with non-radiographic spondyloarthritis (10.5%) compared with AS (4.4%) showed an estimated ‘true’ progression by at least one grade according to both readers, although the difference between the two groups was statistically non-significant. The rate of progression from non-radiographic axial spondyloarthritis to AS was 11.6% over 2 years. An elevated level of C-reactive protein (CRP) at baseline was a strong positive predictor of radiographic sacroiliitis progression in non-radiographic axial spondyloarthritis and AS (OR 3.65 and 5.08, respectively, p<0.05).

Conclusion Progression of radiographic sacroiliitis by at least one grade after 2 years occurs only in a small percentage of patients with early axial spondyloarthritis. An elevated level of CRP was found to be a strong positive predictor of sacroiliitis progression.