Bone and muscle loss in SAPHO syndrome: quantitative analysis and factors associated with vertebral fractures

Background SAPHO syndrome can involve the spine, along with vertebral fractures (VFs), and demonstrates osteoporosis and sarcopenia. However, the relationship between musculoskeletal factors with VFs in SAPHO patients is unclear. Purpose To quantify bone and muscle loss in SAPHO syndrome and identify the factors associated with VFs. Material and Methods The study included 35 patients and 70 age- and sex-matched controls. The bone mineral density (BMD) of the lumbar spine (LS), femoral neck (FN), total hip (TH), the age- and sex-specific T- and Z-scores, and trabecular bone score (TBS) were evaluated using dual-energy X-ray absorptiometry (DXA). Cross-sectional muscle area (CSMA), skeletal muscle radio-attenuation (SMRA), skeletal muscle index (SMI), and skeletal muscle gauge (SMG) were assessed at the T8, T10, and T12 levels based on chest CT scans. The related factors of VFs were analyzed through univariable and multivariable analyses. The diagnostic accuracy of the related factors in VFs was based on receiver operator characteristic (ROC) curves. Results Compared to controls, LS-BMD, FN-BMD, TH-BMD, corresponding T- and Z-scores, and TBS were significantly reduced in women, whereas LS-BMD, T- and Z-scores were significantly increased in men. CSMA, SMI, and SMG at the T8, T10, and T12 levels were significantly reduced in women. LS-BMD and SMG-T12 were independently associated with VFs, and their combination showed the highest diagnostic efficacy for VFs. Conclusion Female SAPHO patients exhibited notable bone and muscle loss, along with bone microstructure damage. LS-BMD and SMG-T12 hold the potential to offer valuable insights for the management of VFs risk in SAPHO patients.