Improvement of bone mineral density and new vertebral fractures during 8 years of TNF-α inhibition in patients with axial spondyloarthritis

Objective: In our prospective cohort with standardized bi-annual measurements of bone mineral density (BMD) and spinal radiographs, we evaluated the long-term course of BMD and the development of radiographic vertebral fractures (VFs) during 8 years of TNFi treatment in patients with radiographic axial spondyloarthritis (r-axSpA). 

Methods: Consecutive axSpA patients from the GLAS cohort receiving TNFi for ≥8 years were included. Patients who received anti-osteoporotic treatment were excluded. Lumbar spine (LS) BMD was assessed at baseline, 1 year and bi-annually using DEXA. Radiographic VFs were evaluated using the Genant classification. 

Results: 126 axSpA patients were included; 75 % male, mean age 42 ± 11 years, ASDAS 3.8 ± 0.8, median LS BMD Z-score -0.5 (IQR -1.4–0.7) and 20 % had radiographic VFs at baseline. Disease activity improved rapidly and sustained. LS BMD Z-score improved significantly up to 4 years compared to the previous time point and sustained thereafter. Median percentage of improvement compared to baseline was 8.9 % (2.8–15.8) and 7.2 % (2.2–14.7) after 4 and 8 years, respectively. Of 90 patients with baseline and 8-year radiographs, 14 (16 %) developed new VFs and 5 (6 %) showed an increase in severity of existing VFs. Of all 44 VFs present at 8 years, 30 % were grade 2 (n = 12) or grade 3 (n = 1). 

Conclusion: In r-axSpA patients treated with TNFi for 8 years, LS BMD Z-score increased significantly, especially during the first 4 year of treatment. Radiographic VFs continued to develop or progressed, irrespective of improvement in BMD. Therefore, clinical attention for trabecular bone loss is important in daily clinical practice.