BMI和SMI在类风湿关节炎继发骨质疏松中的临床研究

目的探讨类风湿关节炎(rheumatoid arthritis,RA)患者的体质量指数(body mass index,BMI)、脂肪质量指数(fat mass index,FMI)和骨骼肌质量指数(skeletal muscle mass index,SMI)与RA患者继发骨质疏松(osteoporosis,OP)的相关性。方法选择RA患者418例,同时选择同期健康体检的158名正常人作为对照组。采用双能X线骨密度仪测量研究对象股骨颈(Neck)、大转子(G.T)、总髋部(Hip)、腰椎1～4(L1、L2、L3、L4)部位的骨密度(bone mineral density,BMD)并参照OP诊断标准进行分级,采用直接节段多频率生物电阻抗测试法测定研究对象的骨骼肌含量、体脂肪、矿物质含量,并计算BMI、FMI和SMI。结果①RA患者各测定部位的BMD均明显低于正常对照组(P0.0001),其OP发生率(42.6%)明显高于对照组(13.9%)(χ~2=41.551,P0.0001)。②RA患者肌少症发生率(54.5%)明显高于对照组(9.0%)(χ~2=96.747,P0.0001)。③不同BMI组RA患者间各部位的BMD、SMI、FMI、矿物质含量、体脂百分比和骨骼肌含量是明显不同的(P0.0001),且随着BMI的增高,上述各指标均呈线性增高趋势(P0.0001)。④在BMI为消瘦的RA患者中,肌少症组中OP发生率与无肌少症组中相近(48.1%vs 45.5%,χ~2=0.027,P=0.870),在BMI为正常、超重或肥胖组中,肌少症组中OP发生率均明显高于无肌少症组(56.6%vs 33.0%,χ~2=12.238,P0.0001;52.6%vs 22.7%,χ~2=10.953,P=0.001)。在有或无肌少症的RA患者中,不同BMI组间RA患者OP发生率无明显差别(P=0.563、0.148)。⑤线性相关分析显示,SMI与各部位的BMD和BMI均呈正直线相关(P0.0001),而与体脂百分比呈负直线相关(P0.0001)。⑥多元Logistic回归分析显示,SMI(OR=0.696,P=0.001,95%CI:0.565～0.857)为RA患者发生OP的保护因素,年龄(OR=1.091,P0.0001,95%CI:1.065～1.117)和性别(OR=5.259,P0.0001,95%CI:2.543～10.876)均为RA患者发生OP的危险因素。结论 BMI、SMI和FMI均与RA患者OP的发生有关,但SMI是RA患者发生OP最重要的保护因素。

Clinical study of associations between BMI, SMI and secondary osteoporosis in patients with rheumatoid arthritis

Objective To explore the associations of body mass index (BMI), fat mass index (FMI), skeletal muscle mass index (SMI) and secondary osteoporosis (OP) in patients with rheumatoid arthritis (RA). Methods Four hundred and eighty patients with RA and 158 normal controls were enrolled. Bone mineral density (BMD) at sites of femur neck (Neck), greater trochanter (G.T), total hip (Hip) and lumbar vertebrae 1-4 (L1, L2, L3, L4) was measured by dual energy X-ray absorptiometry and OP was diagnosed according to the criteria of OP. Skeletal muscle mass, percentage of body fat and mineral content were measured by biological electrical impedance, and BMI, FMI and SMI were calculated. Results RA patients had significantly lower BMD at each site measured than normal controls (P<0.0001), and had significantly higher incidence of OP (42.6%, 178/418) than the control group (13.9%) (?2=41.551, P<0.0001). Incidence of sarcopenia in RA patients was 54.5%, which was significantly higher than that in the control group (9.0%) (?2=96.747, P<0.0001). BMD, SMI, FMI, mineral content, percentage of body fat, skeletal muscle mass and muscle mass of both upper and lower limbs in RA patients among different BMI groups were significantly different (P<0.0001), and there were linear increasing tendencies with increased BMI (P<0.0001). In RA patients with BMI<18.5 kg/m2, incidence of OP in RA patients with sarcopenia was similar to those without sarcopenia (48.1% vs 45.5%, ?2=0.027, P=0.870). In RA patients with normal BMI, or were overweight or obese, incidences of OP in RA patients with sarcopenia was significantly higher than that in RA patients without sarcopenia (56.6% vs 33.0%, ?2=12.238, P<0.0001; 52.6% vs 22.7%, ?2=10.953). In RA patients with or without sarcopenia, there were no significant differences regarding the incidence of OP among different BMI groups (P=0.563, 0.148). Linear correlation analysis showed that there were positive linear correlations between SMI and BMD of each site measured and BMI (P<0.0001), but there was a negative linear correlation between SMI and percentage of body fat (P<0.0001). Logistic regression analysis found that SMI (OR=0.696, P=0.001, 95%CI: 0.565-0.857) was a protective factor for OP in RA, and age (OR=1.091, P<0.0001, 95% CI: 1.065-1.117) and sex (OR=5.259, P<0.0001, 95%CI: 2.543-10.876) were risk factors. Conclusion BMI, SMI and FMI are associated with the occurrence of OP in RA patients, SMI rather than BMI was the most important protective factor for OP in RA.