Background: Sarcopenia and low muscle mass are prevalent and prognostically relevant in patients with lung cancer, yet their diagnosis remains challenging in routine clinical practice. Opportunistic assessment using computed tomography (CT) has emerged as a valuable tool for body composition evaluation. We aimed to assess the utility of thoracic CT at T12 and T4 levels in identifying sarcopenia and low muscle mass and explore their correlation with morphofunctional tools such as bioelectrical impedance vector analysis (BIVA), nutritional ultrasound (NU), and functional performance tests. Methods: In this prospective observational study, 80 patients with lung cancer were evaluated at diagnosis. Body composition was assessed using BIVA-, NU-, and CT-derived parameters at T12 and T4 levels. Functional status was measured using the Timed Up and Go (TUG) and 30-Second Chair Stand Test. Sarcopenia was defined according to EWGSOP2 criteria. Results: Sarcopenia was identified in 20% of patients. CT-derived indices at T12CT demonstrated better diagnostic performance than T4CT. For detecting low muscle mass, the optimal SMI cut-off values were SMI_T12CT < 31.98 cm2/m2and SMI_T4CT < 59.05 cm2/m2in men and SMI_T12CT < 28.23 cm2/m2and SMI_T4CT < 41.69 cm2/m2in women. For sarcopenia diagnosis, the values were SMI_T12CT < 24.78 cm2/m2and SMI_T4CT < 57.23 cm2/m2in men and SMI_T12CT < 21.24 cm2/m2and SMI_T4CT < 49.35 cm2/m2in women. A combined model including SMI_T12CT, RF_CSA, and the 30 s squat test showed high diagnostic accuracy (AUC = 0.826). In multivariable analysis, lower SMA_T12CT was independently associated with risk of sarcopenia (OR = 0.96, 95% CI: 0.92–0.99,p= 0.022), as were older age (OR = 1.23, 95% CI: 1.07–1.47,p= 0.010) and fewer repetitions in the 30 s squat test (OR = 0.78, 95% CI: 0.63–0.91,p= 0.007). Conclusions: CT-derived body composition assessment, particularly at the T12 level, shows good correlation with morphofunctional tools and may offer a reliable and timely alternative for identifying sarcopenia and low muscle mass in patients with lung cancer.
背景：肌肉减少症和低肌肉质量在肺癌患者中普遍存在且与预后相关，但在常规临床实践中其诊断仍具挑战性。利用计算机断层扫描（CT）进行机会性评估已成为身体成分评估的重要工具。本研究旨在评估胸椎T12和T4水平CT在识别肌肉减少症和低肌肉质量方面的效用，并探讨其与生物电阻抗矢量分析（BIVA）、营养超声（NU）和功能性能测试等形态功能工具的相关性。方法：在这项前瞻性观察研究中，对80例初诊肺癌患者进行评估。使用BIVA、NU以及T12和T4水平的CT衍生参数评估身体成分。功能状态通过计时起立行走测试（TUG）和30秒椅子站立测试进行测量。肌肉减少症依据EWGSOP2标准定义。结果：20%的患者被诊断为肌肉减少症。T12水平的CT衍生指标显示出比T4水平更好的诊断性能。对于低肌肉质量的检测，男性最佳骨骼肌指数（SMI）截断值为SMI_T12CT < 31.98 cm²/m²和SMI_T4CT < 59.05 cm²/m²，女性为SMI_T12CT < 28.23 cm²/m²和SMI_T4CT < 41.69 cm²/m²。对于肌肉减少症的诊断，男性截断值为SMI_T12CT < 24.78 cm²/m²和SMI_T4CT < 57.23 cm²/m²，女性为SMI_T12CT < 21.24 cm²/m²和SMI_T4CT < 49.35 cm²/m²。包含SMI_T12CT、股直肌横截面积（RF_CSA）和30秒蹲起测试的联合模型显示出较高的诊断准确性（AUC = 0.826）。在多变量分析中，较低的T12水平骨骼肌面积（SMA_T12CT）与肌肉减少症风险独立相关（OR = 0.96, 95% CI: 0.92–0.99, p = 0.022），年龄较大（OR = 1.23, 95% CI: 1.07–1.47, p = 0.010）和30秒蹲起测试重复次数较少（OR = 0.78, 95% CI: 0.63–0.91, p = 0.007）也是独立相关因素。结论：CT衍生的身体成分评估，尤其是在T12水平，与形态功能工具显示出良好的相关性，可能为识别肺癌患者的肌肉减少症和低肌肉质量提供一种可靠且及时的替代方法。
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