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

https://doi.org/10.1053/j.jrn.2016.02.002Get rights and content

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.

Introduction

Quantification of lean body mass (LBM) is important for research in nutrition and exercise physiology. Total body protein measurement performed by rapid in vivo neutron activation analysis1 is considered the gold standard for measurement of LBM but is technically cumbersome. Other techniques used to estimate muscle mass in dialysis patients include anthropometry, creatinine kinetics, bioimpedance analysis, dual-energy x-ray absorptiometry (DEXA), and imaging techniques.2 Each of these methods has limitations. Anthropometry provides only a crude estimate of muscle mass. Measurement of muscle mass by serum creatinine kinetics is subject to assumptions about extrarenal creatinine excretion and is affected by factors such as dietary intake of animal skeletal muscle.3, 4 Measurement of nonfat tissue mass with bioimpedance analysis and DEXA can be biased by hydration status5 and edema.6 Furthermore, DEXA involves ionizing radiation.

Measurement of muscle mass has been performed with cross-section imaging including computed tomography (CT)7 and magnetic resonance imaging (MRI).8 MRI is advantageous for measurement of muscle mass because it involves no ionizing radiation and therefore does not theoretically increase the risk of cancer as does CT. We have previously used a 3-point Dixon MRI fat/water separation method9 and a soft tissue MRI signal model10 for lean muscle quantification in the legs.11, 12

Measurement of intraabdominal fat volume is especially important in body composition studies because visceral fat is metabolically more active than subcutaneous fat. Measurement of both muscle and fat compartments for body composition with MRI usually requires imaging of the thigh to measure thigh muscle area and a separate abdominal imaging sequence to measure intraabdominal fat area. This is cumbersome as this requires different positioning of the patient and the MRI signal reception coils. For this reason, we sought to determine whether measurement of psoas or paraspinous muscle area at the same L4-L5 axial slice used for abdominal fat measurement will provide a useful measure of whole-body muscle mass. If so, a single MRI section at L4-L5 level could provide clinically relevant information on both muscle and fat compartments in body composition studies.

Section snippets

Study Population and Study Procedures

Protein Intake, Cardiovascular disease and Nutrition In stage V CKD is a prospective observational study (publicly registered as NCT00566670 at clinicaltrials.gov) examining the impact of nutrient intake on vascular health, body composition, and physical functioning in adult (≥18 years) patients on maintenance hemodialysis (MHD) for at least 3 months at the University of Utah outpatient dialysis units. This study is HIPAA compliant and IRB approved, and all subjects have given written informed

Results

The study population consisted of 105 subjects on MHD. Participants underwent MRI of the thighs for measurement of midthigh muscle cross-section area, MRI of the abdomen at L4-L5 for measurement of psoas and paraspinous muscle areas, and DEXA scan to measure whole-body lean mass. Baseline characteristics by the psoas and MTMA groups are summarized in Table 1. In general, younger age, male gender, and African-American race were associated with higher muscle area.

As shown in Figure 2, there was a

Discussion

Muscle mass measurement is used to evaluate nutrition and assess the effect of exercise interventions. Muscle mass has been correlated with functional independence13 and decreased fall risk14 in the elderly and is strongly correlated with survival in MHD patients.15, 16, 17 Hence, measurement of LBM as a measure of muscle mass is useful in both research and clinical settings.

In previous studies, the use of MTMA or volume has been shown to be a reliable measure of muscle mass. In a study of 387

Practical Applications

In body composition studies in which abdominal MRI is performed for characterization of visceral fat, psoas muscle area measured on a single abdominal MR image may be a suitable substitute for time-consuming separate MRI of the legs as a measure of lean muscle mass.

References (24)

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    Support: This study is supported by the following: R01-DK077298 and R01-DK078112 awarded to S.B., K24 DK62849 to T.A.I., 5 K08 CA112449 to G.R.M., University of Utah Study Design and Biostatistics Center, with funding in part from the Public Health Services research grant numbers UL1-RR025764 and 1UL-1RR024975 and C06-RR11234 from the National Center for Research Resources.

    Financial Disclosure: The authors have no conflicts of interest to disclose.

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