Objectives To study the bone mineral density (BMD) and body composition (BC) in Chinese patients with systemic sclerosis (SSc), and the risk factors for low BMD.
Methods Consecutive patients who fulfilled the ACR criteria for SSc were screened for BMD and BC (fat and lean mass) by dual energy X-ray absorptiometry (DXA) scan (Hologic, Belford USA). Exclusion criteria were: (1) Age <18 years; (2) Informed consent could not be obtained. An equal number of age and gender matched healthy controls were also recruited for the same measurements. The extent of skin involvement was assessed by the modified Rodnan skin score (mRSS) and organ damage was evaluated by the Medsger SSc severity index. Risk factors for low BMD were studied by linear regression analyses.
Results 77 patients with SSc and 77 controls were studied (91% women). The mean age of SSc patients was 42.7±14 years and the mean disease duration was 7.8±6.6 years. Sixteen (21%) patients had diffuse SSc while the others had limited SSc. Only 5 (6%) patients were receiving bisphosphonates. According to the WHO criteria, 9 (12%) patients with SSc had osteoporosis (T score ≤-2.5) at the hip and 26 (34%) patients had osteoporosis at the lumbar spine. The incidence of osteoporosis at the hip and lumbar spine was significantly higher than that in normal controls (hip 1%; p=0.008, lumbar spine 14%; p=0.004). Osteopenia of the hip and spine (T score between -1 and -2.5), occurred in 58% and 36%, respectively, of the SSc patients. Four (5%) patients had personal history of fractures, all of which were non-vertebral fractures. The body weight (BW) of patients with SSc was significantly lower than controls (52.5±9.9 vs 56.4±8.3kg; p<0.001). After adjustment for age, body mass index (BMI) and other osteoporosis risk factors, BMD of the total hip (0.786±0.138 vs 0.857±0.118g/m2; p=0.01) and femoral neck (0.674±0.123 vs 0.734±0.117g/m2; p<0.001) were significantly lower in patients with SSc than controls. The BMD of the lumbar spine (L2-4) was also significantly lower in SSc patients (0.894±0.155 vs 0.972±0.148g/m2; p=0.001). On the other hand, the total bone mineral content (BMC) (1.76±0.34 vs 1.92±0.30g; p=0.002) and lean body mass (32.9±5.3 vs 35.1±5.6kg; p=0.01) were significantly lower in patients with SSc than controls. The median mRSS score and total Medsger severity index of the SSc patients was 8 (IQR 4-13) and 3 (IQR 1-6), respectively. Logistic regression analysis revealed a significant correlation between mRSS score and BMD of the total hip (OR 1.12[1.004-1.24] per point; p=0.04) but not with the lumbar spine (OR 1.10[0.996-1.210] per point; p=0.06) after adjustment for age, sex and BMI. The total Medsger severity score correlated positively but insignificantly with osteoporosis of the lumbar spine (OR 1.01[0.87-1.17]; p=0.90) or the hip (OR 1.15[0.98-1.35]; p=0.09). Increasing age was the other independent and adverse factor related to both osteoporosis of the hip and spine (p<0.01 in both).
Conclusions Patients with SSc have significantly lower BMD at lumbar spine, hip and femoral neck, as well as lean body mass than age and gender matched healthy controls. Osteoporosis of the hip correlates significantly with the extent of skin involvement but not with organ damage.
Disclosure of Interest None Declared