Background Syndesmophytes formation and complete fusion of the total spine are common characteristics leading to decrease in axial mobility, functional impairment and disability in ankylosing spondylitis (AS) patients. Predictors for progression of this structural damage are smoking, elevated levels of acute phase reactants and the presence of syndesmophytes at baseline. These predictors identify increased risk for progression at the group level but their specificity is not strong enough to be used as biomarkers in individual patients. We recently demonstrated that calprotectin, a heterodimer of S100A8 and S100A9 which is expressed and secreted during monocyte infiltration into inflamed tissues, is a good biomarker of treatment responses in AS.
Objectives Here, we aimed to determine whether calprotectin levels are predictive for radiographic spinal progression in AS patients.
Methods In total, 76 AS patients were selected from German Spondyloarthritis Inception Cohort (GESPIC) . Lateral views of spinal radiographs were scored by two readers using the modified Stoke Ankylosing Spondylitis Spine Score (mSASSS) system . Subsequently, anteroposterior views of the lumbar spine were scored for the presence of syndesmophytes. Radiographic spinal progression was defined as 1) mSASSS worsening by ≥2 units after 2 years, and 2) development of a new syndesmophyte or progression of existing syndesmophytes (i.e., formation of a bridging syndesmophyte) after 2 years. Levels of serum calprotectin levels were determined by ELISA at baseline.
Results Patients with progression had significantly higher calprotectin serum levels than those without progression: 0.68±0.21 vs. 0.48±0.26, P=0.005. High calprotectin levels were associated with mSASSS worsening over two years in AS, with an Area Under the Curve (AUC) of 0.740 (95% CI 0.614-0.866; P=0.004). The odds ratio (OR) for radiographic spinal progression (mSASSS worsening by ≥2 units) in patients with calprotectin serum level >0.5 μg/ml was 6.2 (95% CI 1.6-24.2, P=0.009).
The association between calprotectin levels and mSASSS progression remained significant after adjusting for the other independent risk factors (syndesmophytes at baseline, elevated C-reactive protein (CRP), and smoking ): OR=5.5 (95% CI 1.2-25.8; P=0.030).
Analysis of syndesmophyte formation and/or progression as outcome for structural damage yielded similar results: patients with new syndesmophytes and/or progression had significantly higher calprotectin levels compared to those without progression: 0.64±0.27 vs. 0.48±0.25, P=0.035. The AUC was 0.670 (95% CI 0.520-0.819; P=0.031).
The predictive value of calprotectin was independent but similar to that of CRP.
Conclusions Calprotectin is an independent predictor for radiographic spinal progression in AS. Compared to CRP, calprotectin is not better in predicting this progression. Furthermore, calprotectin plays a role in inflammation, confirming that radiographic spinal progression is related to inflammation.
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Disclosure of Interest None Declared