Yu Elaine W, Bouxsein Mary L, Roy Adam E, Baldwin Chantel, Cange Abby, Neer Robert M, Kaplan Lee M, Finkelstein Joel S
Department of Medicine, Endocrine Unit, Massachusetts General Hospital, Boston, MA, USA.
J Bone Miner Res. 2014 Mar;29(3):542-50. doi: 10.1002/jbmr.2063.
Several studies, using dual-energy X-ray absorptiometry (DXA), have reported substantial bone loss after bariatric surgery. However, profound weight loss may cause artifactual changes in DXA areal bone mineral density (aBMD) results. Assessment of volumetric bone mineral density (vBMD) by quantitative computed tomography (QCT) may be less susceptible to such artifacts. We assessed changes in BMD of the lumbar spine and proximal femur prospectively for 1 year using DXA and QCT in 30 morbidly obese adults undergoing Roux-en-Y gastric bypass surgery and 20 obese nonsurgical controls. At 1 year, subjects who underwent gastric bypass surgery lost 37 ± 2 kg compared with 3 ± 2 kg lost in the nonsurgical controls (p < 0.0001). Spine BMD declined more in the surgical group than in the nonsurgical group whether assessed by DXA (-3.3 versus -1.1%, p = 0.034) or by QCT (-3.4 versus 0.2%, p = 0.010). Total hip and femoral neck aBMD declined significantly in the surgical group when assessed by DXA (-8.9 versus -1.1%, p < 0.0001 for the total hip and -6.1 versus -2.0%, p = 0.002 for the femoral neck), but no changes in hip vBMD were noted using QCT. Within the surgical group, serum P1NP and CTX levels increased by 82% ± 10% and by 220% ± 22%, respectively, by 6 months and remained elevated over 12 months (p < 0.0001 for all). Serum calcium, vitamin D, and PTH levels remained stable in both groups. We conclude that moderate vertebral bone loss occurs in the first year after gastric bypass surgery. However, striking declines in DXA aBMD at the proximal femur were not confirmed with QCT vBMD measurements. These discordant results suggest that artifacts induced by large changes in body weight after bariatric surgery affect DXA and/or QCT measurements of bone, particularly at the hip.
几项使用双能X线吸收法（DXA）的研究报告称，减肥手术后存在大量骨质流失。然而，体重的大幅下降可能会导致DXA测量的面积骨密度（aBMD）结果出现人为变化。通过定量计算机断层扫描（QCT）评估体积骨密度（vBMD）可能较不易受此类伪影的影响。我们对30例接受Roux-en-Y胃旁路手术的病态肥胖成年人和20例肥胖非手术对照者，使用DXA和QCT前瞻性地评估了腰椎和股骨近端骨密度在1年内的变化。1年后，接受胃旁路手术的受试者体重减轻了37±2kg，而非手术对照组体重减轻了3±2kg（p<0.0001）。无论通过DXA（-3.3%对-1.1%，p=0.034）还是QCT（-3.4%对0.2%，p=0.010）评估，手术组的脊柱骨密度下降幅度均大于非手术组。通过DXA评估时，手术组的全髋和股骨颈aBMD显著下降（全髋为-8.9%对-1.1%，p<0.0001；股骨颈为-6.1%对-2.0%，p=0.002），但使用QCT未发现髋部vBMD有变化。在手术组中，血清I型前胶原氨基端前肽（P1NP）和I型胶原交联C末端肽（CTX）水平在6个月时分别升高了82%±10%和220%±22%，并在12个月内一直保持升高（所有p<0.0001）。两组的血清钙、维生素D和甲状旁腺激素水平均保持稳定。我们得出结论，胃旁路手术后的第一年出现了中度椎体骨质流失。然而，QCT测量的vBMD并未证实股骨近端DXA测量的aBMD显著下降。这些不一致的结果表明，减肥手术后体重的大幅变化所导致的伪影会影响骨密度的DXA和/或QCT测量，尤其是在髋部。
