Quantification of trunk and android lean mass using dual energy x-ray absorptiometry compared to magnetic resonance imaging after spinal cord injury

Abstract

Objective: To determine whether dual energy x-ray absorptiometry (DXA) compared to magnetic resonance imaging (MRI) may accurately quantify trunk lean mass (LM) after chronic spinal cord injury (SCI) and to investigate the relationships between trunk LM, visceral adiposity, trunk fat mass and basal metabolic rate (BMR).

Design: Cross-sectional design and correlational analysis.

Setting: Research setting in a medical center.

Participants: Twenty-two men with motor complete paraplegia (n = 14; T4-T11) and tetraplegia (n = 8; C5-C7) were recruited as part of a clinical trial.

Interventions: Not applicable.

Outcome measures: Trunk and android LM were measured using DXA. The volume of six trunk muscle groups were then measured using MRI to quantify trunk LM-MRI. Subcutaneous and visceral adipose tissue (VAT) cross-sectional areas were also measured using MRI. After overnight fast, BMR was evaluated using indirect calorimetry.

Results: Trunk LM-DXA (24 ± 3.3 kg) and android LM-DXA (3.6 ± 0.7 kg) overestimated (P < 0.0001) trunk LM-MRI (1.7 ± 0.5 kg). Trunk LM-MRI = 0.088* log (trunk LM-DXA)-0.415; r2=0.29, SEE= 0.44 kg, P = 0.007. Trunk LM-MRI = 1.53* android LM-DXA + 0.126; r2=0.26, SEE= 0.21 kg, P = 0.018. Percentage trunk LM-MRI was inversely related to VAT (r=-0.79, P < 0.0001) and trunk fat mass (r=-0.83, P < 0.001). Only trunk LM-DXA was related to BMR (r = 0.61, P = 0.002). Persons with tetraplegia have 13% smaller trunk muscle cross-sectional areas (P = 0.036) compared to those with paraplegia.

Conclusions: Trunk LM-DXA and android LM-DXA overestimated trunk LM-MRI. Percentage trunk LM-MRI, but not LM-DXA, was inversely related to trunk central adiposity. The findings highlight the importance of exercising trunk LM to attenuate cardio-metabolic disorders after SCI.

Keywords: Body composition; DXA; MRI; Spinal cord injury; Trunk lean mass.

Figures

Figure 1

Representative magnetic resonance images of an individual with SCI. The distribution of subcutaneous and visceral adipose tissue. Trunk muscles: back extensor (BE; 1, 2, and 3), erector spinae (ES; 2), multifidus (MF; 3), iliopsoas (IP; 4), external and internal obliques (EIO; 5), and rectus abdominis (RA; 6) were traced and quantified.

Figure 2

Bland-Altman plots between (A) trunk LM-DXA and LM-MRI as well as (B) android LM-DXA and LM-MRI. The dashed line represents the average of mean differences between the two measurements, with the solid lines representing the 95% confidence intervals (mean ± 2*standard deviations).

Figure 3

Relationship between %trunk LM-MRI and parameters of central adiposity. %trunk LM-MRI was strongly inversely related to (A) visceral adipose tissue (VAT; cm2), (B) subcutaneous adipose tissue (SAT; cm2), (C) % trunk fat mass (FM), and (D) trunk fat mass (g).