Background Inflammation and immobility due to pain and stiffness are responsible for bone loss and even vertebral fractures in patients affected by ankylosing spondylitis (AS). Diagnosis of vertebral osteoporosis and the assessment of risk fracture can be difficult in these patients (pts) because the lumbar bone mineral density (BMD) is overestimated by the presence of sindesmophytes. Trabecular bone score (TBS) is a new noninvasively measurement for assessing skeletal microstructure that gives informations about bone quality. 1
Objectives The aim of the study was to investigate the relationship between skeletal microarchitecture, bone density as well as between vertebral fractures, disease activity and functional ability in AS patients
Methods 9 male pts fulfilling ASAS criteria2 for AS (mean age 42±9.2 years, disease duration 8±2.5 years, BASFI 5.8±1.9, BASDAI 6.3±1.4) and 18 controls, sex and age-matched were enrolled in the study during routine screening programs.
All pts were negative for causes of secondary osteoporosis. The BMD (g/cm2) of the lumbar spine (L1-L4) was analyzed by dual-energy X-ray absorptiometry (DXA) scan (Lunar Prodigy) and using the same machine were performed anteroposterior spine analysis to evaluate TBS for L1-L4 using TBS iNsight Medimaps software (Lunar Prodigy). For definition of normal microarchitecture was considered TBS>1.350 units. Finally, lateral radiographs of the spinal column were taken in order to show the presence of vertebral fractures in the thoracic and lumbar spine. Disease activity of pts was measure by Bath Ankylosing Spondylitis Disease Activity (BASDAI) and functional status was assessed using Bath Ankylosing Spondylitis Functional Index (BASFI).
Results The mean values of BMD and TBS resulted significantly highest in patients with AS than in the control group (1.231±0.16 gr/cm2 vs 1.152±0.17 gr/cm2; p<0.04 and 1.070±0.18 units vs 1.332±0.13 units; p<0.05, respectively).
Interestingly, a positive correlation was found between TBS and BASFI (r=0.6, p=0.005). On the contrary, a negative correlations was found between TBS values and BMD (r= -0,5 p<0.02). No correlation was found between TBS and BASDAI. Then the AS patients were divided according to the presence or not of vertebral fractures; in the fractured group (5 pts, 26%) was observed an highest BMD (1.257±0.04 gr/cm2 vs 1.207±0.05 gr/cm2; p=0.02) and a lower TBS value (1.055±0.01 units vs 1.084±0.02 units; p<0.01) in comparison with non fractured group.
Conclusions This study showed a higher BMD value in AS but a poor quality of bone microarchitecture that represents the bone “paradox” of the disease. Trabecular bone score (TBS) is a novel clinical tool/marker that reflects the trabecular bone structure and could provide skeletal informations, that are not captured from the standard BMD measurement at least in AS with vertebral fractures
Roux JP et al. Osteoporosis Int. 2013; 24(9):2455-60.
Sieper J et al. Ann Rheum Dis 2009;68 (6):784-8
Disclosure of Interest None declared