The aim of the study was to investigate the effect of radiographic spinal progression and disease activity on function and spinal mobility in patients with ankylosing spondylitis (AS) treated with tumor necrosis factor-α (TNF-α) inhibitors for up to 10 years.
Patients with AS who participated in 2 longterm open-label extensions of clinical trials with TNF-α inhibitors (43 receiving infliximab and 17 receiving etanercept) were included in this analysis based on the availability of spinal radiographs performed at baseline and at a later timepoint (yr 2, 4, 6, 8, and 10) during followup. Spinal radiographs were scored according to the modified Stoke Ankylosing Spondylitis Spine Score (mSASSS). Function was assessed by the Bath Ankylosing Spondylitis Functional Index (BASFI), spinal mobility by the Bath Ankylosing Spondylitis Metrology Index (BASMI), and disease activity by the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI).
After the initial improvement, BASFI and BASMI remained remarkably stable at low levels over up to 10 years despite radiographic spinal progression. In the generalized mixed effects model analysis, no association between the mSASSS and the BASFI change (β = 0.0, 95% CI -0.03 to 0.03) was found, while there was some effect of mSASSS changes on BASMI changes over time (β = 0.05, 95% CI 0.01-0.09). BASDAI showed a strong association with function (β = 0.64, 95% CI 0.54-0.73) and to a lesser extent, with spinal mobility (β = 0.14, 95% CI 0.01-0.26).
Functional status and spinal mobility of patients with established AS remained stable during longterm anti-TNF-α therapy despite radiographic progression. This indicates that reduction and continuous control of inflammation might be able to outweigh the functional effect of structural damage progression in AS.