A five-year prospective study of spinal radiographic progression and its predictors in men and women with ankylosing spondylitis

Background: Knowledge about predictors of new spinal bone formation in patients with ankylosing spondylitis (AS) is limited. AS-related spinal alterations are more common in men; however, knowledge of whether predictors differ between sexes is lacking. Our objectives were to study spinal radiographic progression in patients with AS and investigate predictors of progression overall and by sex. Methods: Swedish patients with AS, age (mean±SD) 50±13years, were included in a longitudinal study. At baseline and at 5-year follow up, spinal radiographs were graded according to the modified Stoke Ankylosing Spondylitis Spine Score (mSASSS). Predictors were assessed by questionnaires, spinal mobility tests and blood samples. Results: Of 204 patients included, 166 (81%) were re-examined and 54% were men. Men had significantly higher mean mSASSS at baseline and higher mean increase in mSASSS than women (1.9±2.8 vs. 1.2±3.3; p=0.005) More men than women developed new syndesmophytes (30% vs. 12%; p=0.007). Multivariate logistic regression analyses with progression ≥2 mSASSS units over 5years or development of new syndesmophytes as the dependent variable showed that presence of baseline AS-related spinal radiographic alterations and obesity (OR 3.78, 95% CI 1.3 to 11.2) were independent predictors of spinal radiographic progression in both sexes. High C-reactive protein (CRP) was a significant predictor in men, with only a trend seen in women. Smoking predicted progression in men whereas high Bath Ankylosing Spondylitis Metrology Index (BASMI) and exposure to bisphosphonates during follow up (OR 4.78, 95% CI 1.1 to 20.1) predicted progression in women. Conclusion: This first report on sex-specific predictors of spinal radiographic progression shows that predictors may partly differ between the sexes. New predictors identified were obesity in both sexes and exposure to bisphosphonates in women. Among previously known predictors, baseline AS-related spinal radiographic alterations predicted radiographic progression in both sexes, high CRP was a predictor in men (with a trend in women) and smoking was a predictor only in men.