BONE MINERAL DENSITY AND TRABECULAR BONE SCORE IN TWO SUBSETS OF SYSTEMIC SCLEROSIS PATIENTS

Background: Data concerning the relationship between Systemic Sclerosis (SSc) and alterations of Bone Mineral Density (BMD) are very conflicting. The established standard for measuring BMD is Dual X-ray Absorptiometry (DXA), but it does not provide any informations about the bone microarchitecture, which is a parameter very difficult to evaluate in clinical practice but it is essential to define bone strength. The Trabecular Bone Score (TBS) is a new structural parameter that can be obtained by DXA scanning and it is related to bone microarchitecture and provides data on bone quality irrespective of bone density. Objectives: The aim of this study is to evaluate the differences in BMD and TBS values in two subsets of patients with SSc (limited and diffuse cutaneous disease – lSSc and dSSc) and to analyse their possible relationship with the parameters of body mass composition and phospho-calcium metabolism. Methods: 64 post-menopausal patients classified according to Leroy as limited cutaneous (lSSc) or diffuse cutaneous (dSSc) SSc, were recruited. The following clinical parameters were evaluated: internal organ involvement, degree of skin involvement (Rodnan Skin Score), bone mass index (BMI). For each recruited patient, spine and hip BMD, TBS and body mass composition (lean and fat mass, total bone mineral content - BMC) were assessed by DXA. Serum calcium, phosphorus, alkaline phosphatase, intact parathyroid hormone (PTH) and 25-hydroxyvitamin D (25 OHD) were also measured. Results: BMD at femoral neck and spine was significantly higher in lSSc compared to dSSc patients (p<0,04). In lSSc subjects also BMC was significantly higher compared to dSSc ones (p<0,01) but, interestingly the TBS was significantly lower (p<0,03). lSSc patients presented a higher values of fat mass compared to dSSc (p<0,05), with a slightly higher BMI (which did not reach statistical significance). 25OH serum levels were higher in lSSc group, whereas no differences between lSSc and dSSc in serum calcium, phosphorus, alkaline phosphatase were observed. Conclusions: The presented preliminary data show that in SSc patients with limited cutaneous disease, the BMD values are higher compared to patient with diffuse cutaneous disease; nevertheless in this subset (lSSc) bone quality seem to be reduced, as TBS values are significantly lower. Higher BMC values and serum 25OHD levels observed in lSSc patients could be among the factors that contribute to increasing BMD in this clinical subset. Further analysis should be performed to identify the possible causes of the reduced bone quality in spite of higher BMD in lSSc patients, such as the study of serum adipokines, considering that the presented data show a great fat mass in patients with limited cutaneous disease.