Opportunistic muscle density assay during CT lung cancer screening for low muscle quality evaluation in older adults: a multicenter study

Abstract

Background

Intramuscular adiposity, which can be reflected by muscle computed tomography (CT) attenuation, may be a marker of sarcopenia. This study aimed to investigate muscle attenuation across the life course and thresholds of muscle attenuation for evaluating low muscle quality in older adults.

Methods

This retrospective multicenter study included 9701 subjects aged 20 years and older who underwent CT lung cancer screening from 2019 to 2021 at our institutions in cohort 1. Muscle attenuation (Hounsfield units [HUs]) of the bilateral erector spinae and spleen attenuation at the middle level of the T11 vertebra were measured. The T score, which is analogous to that used to define osteoporosis, was calculated on the basis of absolute muscle attenuation and the muscle‒spleen ratio (M/S). A T score < -2.5 was used to define low muscle density. The cutoff points for muscle CT attenuation and M/S were subsequently calculated to define low muscle density. Another cohort (cohort 2) of 2006 subjects aged 50 years or older was included to explore the association between low muscle quality and vertebral compression fracture (VCF).

Results

The mean [SD] age of cohort 1 was 51.8 [15.5] years, and 5896 [60.8%] men were included. The mean [SD] age of cohort 2 was 62.4 [9.6] years, and 1162 [57.9%] men were included. Multiple linear regression analysis revealed that age was associated with muscle CT attenuation (β = -0.19, 95% confidence interval (CI): -0.21 to -0.18) and the M/S ratio (β = -0.004, 95% CI: -0.004 to -0.003). The prevalence of low muscle density was dependent on the cutoff point and increased with age. A cutoff point of 32 HU for women and 37 HU for men and an M/S of 0.65 for women and 0.75 for men were used to define low muscle density. Low muscle density defined by those cutoff points was associated with the risk of VCF [muscle attenuation: adjusted hazard ratio (aHR) = 0.422 (95% CI: 0.256–0.696) for women; aHR = 0.391 (95% CI: 0.173–0.883) for men; M/S: aHR = 0.40 (95% CI: 0.23–0.68) for women; aHR = 0.23 (95% CI: 0.09–0.58) for men].

Conclusion

Muscle density decreases with age. The muscle attenuation of 32 HU for women and 37 HU for men, an M/S of 0.65 for women and 0.75 for men, may be used to define low muscle density.