Relationship Between Inflammation and Radiographic Progression in Patients With Ankylosing Spondylitis Attaining a BASDAI of Less Than 4 During Tumor Necrosis Factor Inhibitor Treatment.

Objective: To determine the relationship between inflammation and radiographic progression over time in patients with ankylosing spondylitis (AS) attaining a Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) of < 4 during tumor necrosis factor inhibitor (TNFi) treatment.

Methods: Medical records data of patients with AS with BASDAI scores of < 4 during TNFi treatment were analyzed 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 2956 intervals were obtained from 333 patients. Among different lag times, the cumulative sum of log CRP in the previous 18 to 36 months associated with mSASSS showed significant beta coefficients. In the final linear mixed model, the cumulative sum of log CRP in the previous 24 months was significantly associated with mSASSS at 24 months (β 0.04, 95% CI 0.01-0.07, = 0.004).

Conclusion: Remnant inflammation correlates with radiographic progression, even in patients attaining a BASDAI of < 4 during TNFi treatment. CRP is a surrogate marker for radiographic progression despite clinical improvement with TNFi treatment.