Bone Density in Ankylosing Spondylitis Save

Ankylosing spondylitis (AS) is a burden on the bones—both literally and diagnostically. The disease’s dual nature, marked by chronic inflammation and abnormal new bone formation, complicates the assessment of bone health. While inflammation erodes trabecular bone, syndesmophytes and ligamentous calcifications can falsely elevate spine bone mineral density (BMD) readings on standard dual-energy X-ray absorptiometry (DXA). This paradox means that patients with structurally fused spines may appear to have “normal” bone density despite being at high risk for fractures.

At ACR25, a retrospective study from China tackled this challenge using quantitative computed tomography (QCT), a more precise imaging modality that measures true volumetric bone density unaffected by cortical ossifications. 

The study followed 53 AS patients—30 treated with the IL-17 inhibitor secukinumab and 23 with the TNF-α inhibitor adalimumab—over 12 months. Both therapies significantly reduced inflammatory markers (CRP and ESR, P < 0.01), with secukinumab showing greater declines in systemic immune-inflammation index (SII) and platelet-to-lymphocyte ratio (PLR). However, neither treatment produced significant overall changes in thoracolumbar BMD. Adalimumab led to a modest gain at the T4 vertebral level, but overall longitudinal changes in BMD were not statistically significant in either group, and no significant intergroup differences were observed.

Importantly, baseline inflammatory markers did not correlate with heterogeneity in BMD response to either biologic agent. This suggests that short-term biologic therapy may not directly translate into measurable skeletal protection and underscores the need for longer-term studies. The most clinically relevant takeaway from this study is that QCT should be the preferred method—not lumbar DXA—for assessing bone density in AS. QCT provides a more reliable evaluation of trabecular bone health, even in patients with advanced spinal fusion. Regular bone density monitoring should be considered essential in the management of AS, especially given the limitations of conventional imaging and the silent progression of skeletal fragility.