Making the invisible visible: imaging techniques for assessing muscle mass and muscle quality in chronic kidney disease

Abstract

Muscle wasting and low muscle mass are prominent features of protein energy wasting (PEW), sarcopenia and sarcopenic obesity in patients with chronic kidney disease (CKD). In addition, muscle wasting is associated with low muscle strength, impaired muscle function and adverse clinical outcomes such as low quality of life, hospitalizations and increased mortality. While assessment of muscle mass is well justified, the assessment of skeletal muscle should go beyond quantity. Imaging techniques provide the means for non-invasive, comprehensive, in-depth assessment of the quality of the muscle such as the infiltration of ectopic fat. These techniques include computed tomography (CT), magnetic resonance imaging (MRI) and ultrasound. Dual energy X-ray absorptiometry is also an imaging technique, but one that only provides quantitative and not qualitative data on muscle. The main advantage of imaging techniques compared with other methods such as bioelectrical impedance analysis and anthropometry is that they offer higher precision and accuracy. On the other hand, the higher cost for acquiring and maintaining the imaging equipment, especially CT and MRI, makes these less-used options and available mostly for research purposes. In the field of CKD and end-stage kidney disease (ESKD), imaging techniques are gaining attention for evaluating muscle quantity and more recently muscle fat infiltration. This review describes the potential of these techniques in CKD and ESKD settings for muscle assessment beyond that of muscle quantity.

Keywords: chronic kidney disease; computed tomography; magnetic resonance imaging; muscle wasting; ultrasound.

Figure 1:

Muscle assessment and possible nutrition and muscle abnormalities. Muscle mass can be assessed by anthropometry (ANT), biolectrical impedance analysis (BIA) and dual energy X-ray absorptiometry (DXA) , while muscle area is assessed by computed tomography (CT), magnetic resonance imaging (MRI) and ultrasound (US). These can diagnose normal muscle mass/area and muscle wasting. Individuals with normal muscle mass/area can still have muscle abnormalities if there is fat infiltrated in the muscle. The latter can be assessed by CT, MRI or US and leads to decreased muscle contractile area with consequent low muscle strength, low muscle function and low muscle quality. On the other hand, if muscle wasting is present, other nutrition and muscle abnormalities can co-exist, including PEW, sarcopenia and sarcopenic obesity. Muscle fat infiltration can also be present in these three later conditions with concomitant low muscle strength, low muscle function and low muscle quality.

Figure 2:

Body composition assessment by computed tomography (CT) at L3. (A) Skeletal muscle area at L3 using a range of −29–150 HU. (B) Different body compositions assessed by CT at L3.

Figure 3:

Body composition assessment by quadriceps muscle ultrasound (US). (A) Rectus femoris and vastus intermedius muscle thickness. (B) Rectus femoris cross-sectional area. (C) Fascicle length. (D) Pennation angle. (E) Echogenicity evaluation.