Background: Single cross-sectional area of muscle at the third lumbar vertebra (L3MA) is gold standard to estimate skeletal muscle mass (SMM), and L3 muscle index (L3MI, L3MA/height(2)) is used to determine sarcopenia. The purposes of this study were to evaluate the relationship between SMM indices determined by routine chest CT and L3MI in patients with small-cell lung cancer (SCLC) and to suggest chest CT-derived diagnostic criteria for sarcopenia.
Methods: Area of pectoralis muscles at the aortic arch (PMA) and at L1 (L1MA) was retrospectively measured on chest CT images of 90 consecutive SCLC patients. Pearson's correlation and multiple linear regression analysis were used to assess relationships between L3MI determined by PET/CT and pectoralis muscle index (PMI) and L1 muscle index (L1MI) determined by chest CT.
Results: The correlation between L1MI and L3MI was stronger than that between PMI and L3MI (r = 0.851 vs. r = 0.447, p < 0.001). Multivariable regression analysis showed that L1MI was the only significant predictor of L3MI; L3MI = 0.963 × L1MI + 10.336 (R (2) = 0.689, p < 0.001) for male and L3MI = 0.772 × L1MI + 16.518 (R (2) = 0.777, p < 0.001) for female. Using this relationship, estimated cutoffs of L1MI for sarcopenia were 46 cm(2)/m(2) for male and 29 cm(2)/m(2) for female (L3MI cutoffs for sarcopenia are 55 cm(2)/m(2) for male and 39 cm(2)/m(2) for female). The sensitivity and specificity of L1MI cutoffs to determine sarcopenia were 98.2 and 100 %, respectively.
Conclusions: Chest CT-determined L1MI is highly correlated with L3MI in SCLC patients. L1MI, as determined by chest CT, could be used to determine the presence of sarcopenia with suggested cutoffs of 46 cm(2)/m(2) for men and 29 cm(2)/m(2) for women.
Keywords: Cancer cachexia; Sarcopenia; Skeletal muscle mass; Small-cell lung cancer; Tomography; X-ray computed.