Yonsei University College of Medicine, Seoul, Korea.
Division of Endocrinology, Endocrine Research Institute, Department of Internal Medicine, Yonsei University College of Medicine, Seoul, Korea.
Endocrinol Metab (Seoul). 2021 Dec;36(6):1201-1210. doi: 10.3803/EnM.2021.1206. Epub 2021 Dec 13.
A decrease in computed tomography (CT)-derived skeletal muscle radiodensity (SMD) reflects age-related ectopic fat infiltration of muscle, compromising muscle function and metabolism. We investigated the age-related trajectory of SMD and its association with vertebral trabecular bone density in healthy adults.
In a cohort of healthy adult kidney donors aged 19 to 69 years (n=583), skeletal muscle index (SMI, skeletal muscle area/height2), SMD, and visceral-to-subcutaneous fat (V/S) ratio were analyzed at the level of L3 from preoperative CT scans. Low bone mass was defined as an L1 trabecular Hounsfield unit (HU) <160 HU.
L3SMD showed constant decline from the second decade (annual change -0.38% and -0.43% in men and women), whereas the decline of L3SMI became evident only after the fourth decade of life (-0.37% and -0.18% in men and women). One HU decline in L3SMD was associated with elevated odds of low bone mass (adjusted odds ratio, 1.07; 95% confidence interval, 1.02 to 1.13; P=0.003), independent of L3SMI, age, sex, and V/S ratio, with better discriminatory ability compared to L3SMI (area under the receiver-operating characteristics curve 0.68 vs. 0.53, P<0.001). L3SMD improved the identification of low bone mass when added to age, sex, V/S ratio, and L3SMI (category-free net reclassification improvement 0.349, P<0.001; integrated discrimination improvement 0.015, P=0.0165).
L3SMD can be an early marker for age-related musculoskeletal changes showing linear decline throughout life from the second decade in healthy adults, with potential diagnostic value for individuals with low bone mass.
计算机断层扫描（CT）得出的骨骼肌放射密度（SMD）降低反映了与年龄相关的肌肉异位脂肪浸润，从而影响肌肉功能和代谢。我们研究了健康成年人中 SMD 的年龄相关轨迹及其与椎体小梁骨密度的关系。
在一项年龄在 19 至 69 岁的健康成年肾脏供体队列中（n=583），我们分析了术前 CT 扫描 L3 水平的骨骼肌指数（SMI，骨骼肌面积/身高 2）、SMD 和内脏到皮下脂肪比（V/S）。低骨量定义为 L1 小梁 HU<160 HU。
L3SMD 从 20 岁开始呈现出持续下降的趋势（男性和女性每年分别下降 0.38%和 0.43%），而 L3SMI 的下降在 40 岁以后才变得明显（男性和女性每年分别下降 0.37%和 0.18%）。L3SMD 降低 1 HU 与低骨量的发生几率增加相关（校正比值比，1.07；95%置信区间，1.02 至 1.13；P=0.003），独立于 L3SMI、年龄、性别和 V/S 比，且具有优于 L3SMI 的区分能力（受试者工作特征曲线下面积 0.68 与 0.53，P<0.001）。L3SMD 可改善年龄、性别、V/S 比和 L3SMI 用于识别低骨量的能力（无类别净重新分类改善 0.349，P<0.001；综合判别改善 0.015，P=0.0165）。
L3SMD 可能是与年龄相关的肌肉骨骼变化的早期标志物，在健康成年人中，从 20 岁开始，其线性下降贯穿整个生命过程，对于低骨量个体具有潜在的诊断价值。
