Increases in C-reactive Protein Levels are Correlated with Radiographic Progression in Patients with Ankylosing Spondylitis who Achieved Clinical Remission with Tumor Necrosis Factor Inhibitor Treatment

Abstract

Objectives: To determine the relationship between inflammation and radiographic progression over time in patients in clinical remission for ankylosing spondylitis (AS) after tumor necrosis factor inhibitor (TNFi) treatment.Method: Medical records data of AS patients with Bath Ankylosing Spondylitis Disease Activity Index scores <4 during TNFi treatment were analysed at 6-month intervals from January 2001 to December 2018. To determine the relationship between the modified Stoke Ankylosing Spondylitis Spinal Score (mSASSS) and C-reactive protein (CRP) over time, we fitted linear mixed models with mSASSS as the response variable, baseline mSASSS and the cumulative sum of CRP with different lag times (6, 12, 18, 24, 30, and 36 months) as fixed effects, and patients as random effects. Associations between mSASSS and the cumulative sum of CRP or the lag times with the highest beta coefficients were further investigated with linear mixed models that included additional clinical variables.Results: A total of 2,956 intervals were obtained from 333 patients. Among different lag times, the cumulative sum of log CRP in the previous 18–36 months and mSASSS showed significant beta coefficients. In the final linear mixed model that included clinical variables, the cumulative sum of log CRP in the previous 24 months was significantly associated with mSASSS at 24 months (β=0.043, 95% CI: 0.014–0.071, p=0.004). Conclusion: Remnant inflammation correlates with radiographic progression even in patients in clinical remission with TNFi treatment. CRP is a surrogate marker for radiographic progression despite clinical improvement with TNFi treatment.