Trabecular Bone Score in Female Patients with Systemic Sclerosis: Comparison with Rheumatoid Arthritis and Influence of Glucocorticoid Exposure

Objective. Systemic sclerosis (SSc) is associated with an increased risk of osteoporosis and fractures. To date, the etiology of bone loss in SSc is unclear. Trabecular bone score (TBS) provides an indirect measurement of bone microarchitecture, independent of areal bone mineral density (aBMD). The aims were to assess bone involvement in SSc using TBS in comparison with a " high-risk" population with rheumatoid arthritis (RA) and controls, and to investigate the determinants of a low TBS. Methods. This was a cross-sectional study of 65 women with SSc, 138 age-matched female patients with RA, and 227 age-matched female controls. Spine and hip aBMD were assessed using dual-energy X-ray absorptiometry. TBS was calculated from the anteroposterior image of the spine aBMD. Results. TBS was significantly lower in SSc compared to controls (p < 0.0001) and did not differ from RA (p = 0.128), despite lower cumulative and daily glucocorticoid (GC) dose (p < 0.0001). Further, patients with SSc receiving GC >= 5 mg/day had a significantly lower TBS than those receiving GC < 5 mg/day (p = 0.001). Multivariate analysis revealed that a low TBS was independently associated with daily GC dose (OR 5.6, 95% CI 1.7-19.2) and a T score <= -2.5 SD (OR 5.0, 95% CI 1.5-7.0) in SSc. No association between GC and TBS was found in RA. Conclusion. Our results support the development of a combined approach using both TBS and aBMD for the assessment of bone microarchitecture in inflammatory rheumatic diseases. Our study showed that SSc-related bone involvement is characterized by an impairment in bone quality in addition to reduced bone quantity, and highlights that TBS can identify the negative effect of GC on bone microarchitecture.