Background/Purpose: Axial spondyloarthritis (AxSpA), a chronic inflammatory rheumatic disease causes abnormal bone growth at the spine and paradoxically has been linked to osteoporosis and fragility fractures. While tumor necrosis factor alpha inhibitors have been shown to improve skeletal health in patients with AxSpA, the effect of newer medications that block interleukin-17 (IL17) on bone metabolism remains unclear. This prospective study investigated the impact of IL17 blockade on bone density (BMD) and microarchitecture in AxSpA. We hypothesized that treatment initiation would be associated with improved BMD and microarchitecture.

Methods: Skeletal assessments included areal BMD (aBMD) and trabecular bone score (TBS) by DXA, volumetric BMD (vBMD) and microarchitecture by high-resolution peripheral quantitative computed tomography (HRpQCT2) at baseline and 12-months. DXA and HRpQCT measurements from patients were compared to those of age-matched individuals in reference cohorts. Changes in imaging parameters were compared using Wilcoxon and paired t-tests, and predictors of change in HRpQCT were analyzed using multivariate linear regression.

Results: Of the 22 AxSpA participants, 55% were female (33% postmenopausal), mean age 40 years, and mean BMI 30 kg/m². 55% were HLA-B27 positive, mean symptom duration was 10 years, and C-reactive protein (CRP) was elevated in 32% of participants, respectively. At baseline, mean DXA and HRpQCT Z-scores were within 1 standard deviation of sex and age matched controls. At 12-months, >80% of participants reported 100% medication adherence. Standardized assessments of disease activity improved, with a decrease in Bath Ankylosing Spondylitis Disease Activity (BASDAI -33%, p< 0.01) and Metrology Index (BASMI -22%, p=0.01). In contrast, there was no significant improvement in aBMD, TBS, or microarchitecture by HRpQCT. In fact, decreases were observed in radial total vBMD (-2%, p=0.04) and trabecular vBMD (-2%, p=0.04). Radial trabecular separation tended to increase (4%, p=0.06). Elevated CRP tended to be associated with decrease in total vBMD (tibia R²=0.2, p=0.06; radius R²=0.3, p=0.09).

Conclusion: In summary, participants with AxSpA who began IL17 blockade had significant improvements in clinical symptoms, but no change or small declines in BMD and microarchitecture. Our uncontrolled study lacks data regarding whether treatment attenuated skeletal declines. Larger controlled studies are needed to investigate the long-term skeletal effects of IL-17 blockade.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/effects-of-il-17-blockade-on-skeletal-microarchitecture-in-patients-with-axial-spondyloarthritis-an-hr-pqct-study/