Bone mineral density improves during 2 years of treatment with bisphosphonates in patients with ankylosing spondylitis

Aims: To evaluate whether 2 years of treatment with bisphosphonates in combination with calcium/vitamin D supplements has an effect on lumbar spine and hip bone mineral density (BMD) in ankylosing spondylitis (AS) patients starting tumour necrosis factor-α inhibitors or receiving conventional treatment. Secondly, to explore the development of radiographic vertebral fractures. 

Methods: Patients from the Groningen Leeuwarden AS cohort receiving bisphosphonates based on clinical indication and available 2-year follow-up BMD measurements were included. BMD of lumbar spine (L1–L4) and hip (total proximal femur) were measured using dual-energy X-ray absorptiometry. Spinal radiographs (Th4–L4) were scored for vertebral fractures according to the Genant method. 

Results: In the 20 included patients (median 52 years, 14 males), lumbar spine and hip BMD Z-scores increased significantly; median from −1.5 (interquartile range [IQR] −2.2 to 0.4) to 0.1 (IQR −1.5 to 1.0); P <.001 and median from −1.0 (IQR −1.6 to −0.7) to −0.8 (IQR −1.2 to 0.0); P =.006 over 2 years, respectively. In patients also treated with tumour necrosis factor-α inhibitors (n = 11), lumbar spine and hip BMD increased significantly (median 2-year change +8.6% [IQR 2.4 to 19.6; P =.009] and +3.6% [IQR 0.7–9.0; P =.007]). In patients on conventional treatment (n = 9), lumbar spine BMD increased significantly (median 2-year change +3.6%; IQR 0.7 to 9.0; P =.011) and no improvement was seen in hip BMD (median −0.6%; IQR −3.1 to 5.1; P =.61). Overall, younger AS males with limited spinal radiographic damage showed most improvement in lumbar spine BMD. Four mild radiographic vertebral fractures developed in 3 patients and 1 fracture increased from mild to moderate over 2 years in postmenopausal women and middle-aged men. 

Conclusion: This explorative observational cohort study in AS showed that 2 years of treatment with bisphosphonates in combination with calcium/vitamin D supplements significantly improves lumbar spine BMD. Mild radiographic vertebral fractures still occurred.