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Psoas Muscle Cross-sectional Area as a Measure of Whole-body Lean Muscle Mass in Maintenance Hemodialysis Patients.

OBJECTIVE
We investigate whether psoas or paraspinous muscle area measured on a single L4-L5 image is a useful measure of whole lean body mass (LBM) compared to dedicated midthigh magnetic resonance imaging (MRI).


DESIGN
Observational study.


SETTING
Outpatient dialysis units and a research clinic.


SUBJECTS
One hundred five adult participants on maintenance hemodialysis. No control group was used.


INTERVENTION
Psoas muscle area, paraspinous muscle area, and midthigh muscle area (MTMA) were measured by magnetic resonance imaging.


MAIN OUTCOME MEASURE
LBM was measured by dual-energy absorptiometry scan.


RESULTS
In separate multivariable linear regression models, psoas, paraspinous, and MTMA were associated with increase in LBM. In separate multivariate logistic regression models, C statistics for diagnosis of sarcopenia (defined as <25th percentile of LBM) were 0.69 for paraspinous muscle area, 0.81 for psoas muscle area, and 0.89 for MTMA. With sarcopenia defined as <10th percentile of LBM, the corresponding C statistics were 0.71, 0.92, and 0.94.


CONCLUSIONS
We conclude that psoas muscle area provides a good measure of whole-body muscle mass, better than paraspinous muscle area but slightly inferior to midthigh measurement. Hence, in body composition studies a single axial MR image at the L4-L5 level can be used to provide information on both fat and muscle and may eliminate the need for time-consuming measurement of muscle area in the thigh.