TNF inhibitors reduce spinal radiographic progression in patients with radiographic axial spondyloarthritis: a longitudinal analysis from the ALBERTA FORCAST cohort

AIM: To investigate whether TNF inhibitors (TNFi) impact spinal radiographic progression in patients with axial spondyloarthritis (axSpA) and whether this is coupled to their effect on inflammation.

METHODS: Patients with axSpA fulfilling the modified New York criteria were included in this prospective cohort (ALBERTA FORCAST). Spine radiographs, done every 2 years up to 10 years, were scored by 2 central readers, using the modified Stoke Ankylosing Spondylitis Spine Score (mSASSS). The indirect effect of TNFi on mSASSS was evaluated with generalized estimating equations by testing the interaction between TNFi and ASDAS at the start of each 2-year interval (t). If significant, the association between ASDAS at t and mSASSS at the end of the interval (t+1) was assessed in: i. patients treated with TNFi in all visits; ii. some visits and iii. never treated. In addition, the association between TNFi at t and mSASSS at t+1 (adjusting for ASDAS at t) was also tested (direct effect).

RESULTS: In total, 314 patients were included. A gradient was seen for the effect of ASDAS at t on mSASSS at t+1 (interaction p-value 0.10), with a higher progression in patients never treated with TNFi [β (95% CI): 0.41 (0.13; 0.68)] compared to those continuously treated [0.16 (0.00;0.31)] (indirect effect). However, TNFi also directly slowed progression as treated patients had on average 0.85 mSASSS-units less on t+1 compared to those not treated [-0.85 (-1.35; -0.35)].

CONCLUSION: TNFi reduce spinal radiographic progression in patients with radiographic axSpA which might be partially uncoupled from their effects on ASDAS inflammation.