The Natural Course of Radiographic Progression in Ankylosing Spondylitis — Evidence for Major Individual Variations in a Large Proportion of Patients

Abstract

To describe the natural course of radiographic progression and to differentiate rates of progression in patients with ankylosing spondylitis (AS). Overall, 146 patients with AS who had never received anti-tumor necrosis factor therapy were analyzed in this retrospective cohort study. The main inclusion criterion was the availability of complete sets of cervical and lumbar radiographs from at least 2 timepoints within 6 years. Using the modified Stoke Ankylosing Spondylitis Spine Score (mSASSS), we quantified the structural changes and assessed different rates of radiographic progression based on development of new syndesmophytes/year. The mean followup time was 3.8 +/- 1.7 years (range 1-6) and the mean number of consecutive radiographs was 2.7 (range 2-6) per patient. The mean mSASSS change/year was 1.3 +/- 2.5 units. Radiographic progression showed much variability, since 43% of patients showed a 4-fold greater rate of progression than the mean, and 23% had no progression. The data-based definition for "fast progression" was calculated as a change > 5 mSASSS units or > 2 new syndesmophytes; for "moderate progression" as change of 2.0-5.0 mSASSS units or < 2 new syndesmophytes; and for "slow progression" as change of < 2 mSASSS units or no more than 1 new syndesmophyte within 2 years. The only factor to predict future radiographic progression was the number of syndesmophytes at baseline. Radiographic progression in AS is rather variable and many patients show high rates of progression. On the basis of this retrospective dataset we propose to differentiate patients on an individual level according to their progression rates: patients with fast, moderate, and slow radiographic progression, assessed by counting new syndesmophytes. Predicting radiographic progression remains difficult; only the prevalence of syndesmophytes at baseline is predictive of future damage.