Background/Purpose: Ankylosing spondylitis (AS) is characterized by dysregulated bone remodeling, encompassing both osteolysis and heterotopic new bone formation. The differential effects of interleukin-17 (IL-17) inhibition versus tumor necrosis factor-α (TNF-α) inhibition on bone mineral density (BMD) in patients with AS remain inadequately characterized. This study aimed to compare the 1-year effects of secukinumab (an IL-17 inhibitor) and adalimumab (a TNF-α inhibitor) on BMD in patients with AS and to assess baseline inflammatory biomarkers as predictors of BMD changes.

Methods: This retrospective cohort study enrolled 53 patients with AS receiving either secukinumab (n=30) or adalimumab (n=23). Baseline demographic and clinical characteristics, inflammatory biomarkers (C-reactive protein [CRP], erythrocyte sedimentation rate [ESR]), and thoracolumbar spine BMD (assessed by quantitative computed tomography [QCT]) were collected. Changes in BMD and inflammatory markers at 12 months post-treatment initiation were evaluated using paired t-tests or Wilcoxon signed-rank tests. Intergroup differences in outcomes and correlations between baseline CRP levels and BMD changes were analyzed.

Results: Both treatment modalities resulted in significant reductions in CRP and ESR levels at 12 months (P< 0.01 for all). While no significant intergroup difference in anti-inflammatory efficacy, as measured by CRP and ESR, was detected, secukinumab treatment was associated with significantly greater reductions in the systemic immune-inflammation index (SII; mean change: −235.79 vs. −64.81, P=0.006) and the platelet-to-lymphocyte ratio (PLR; mean change: −28.87 vs. +1.92, P=0.012) compared to adalimumab. Adalimumab was associated with a modest, statistically significant increase in BMD at the T4 vertebral level (+6.38 mg/cm³, P=0.029). However, overall longitudinal changes in thoracolumbar BMD were not statistically significant in either group, and no significant intergroup differences in BMD trajectories were observed. Baseline inflammatory markers did not correlate with heterogeneity in BMD response to either biologic agent.  

Conclusion: Secukinumab and adalimumab demonstrated comparable efficacy in reducing systemic inflammation in patients with AS over a 1-year period, although secukinumab effected greater reductions in composite inflammatory indices (SII and PLR). No clinically significant differences in thoracolumbar BMD changes were observed between the treatment groups during the study. These data suggest that, within this 12-month timeframe, IL-17 and TNF-α inhibition exert similar effects on overall BMD in patients with AS, without evidence of differential skeletal-protective effects.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-impact-of-secukinumab-on-bone-density-in-patients-with-ankylosing-spondylitis-a-1-year-retrospective-study/