Myosteatosis and not low muscle mass is associated with lower survival in kidney transplant recipients

Abstract

Background

Myosteatosis, that is muscle fat infiltration, is an important marker of muscle quality, affecting quality of life and survival in patients with chronic kidney disease (CKD). However, the connection between myosteatosis, skeletal muscle index (SMI) and survival in kidney transplant (KTx) recipients remains unclear.

Methods

This retrospective observational study included a cohort of consecutive adult kidney recipients transplanted between 2010 and 2017 in Stockholm. Preoperative abdominal computed tomography (CT) images obtained after diagnosis of CKD 5 and within 36 months of transplantation were collected. Using established criteria, we measured muscle area at the third lumbar vertebra (L3 level) and identified low attenuation muscle, indicating myosteatosis. Each area was divided by height squared providing the SMI, and fatty muscle index (FMI). Given that there is no commonly accepted definition of sarcopenia, two cut-offs for SMI were used to define low muscle mass, Cut-off 1 (≤32.8 for women and ≤44.7 for men) and Cut-off 2 (≤38.5 for women and ≤52.4 for men). Average radiodensity of skeletal muscle and Charlson comorbidity index were calculated for each patient. The influence on survival from SMI, FMI, SMI/FMI ratio, and radiodensity was analysed.

Results

Out of 582 KTx recipients, 266 (46%) had a pre-transplant abdominal CT available. Applying SMI Cut-off 1, 30 recipients (11%) had sarcopenia compared with 106 (40%) with Cut-off 2. Neither SMI nor FMI was associated with survival. Yet there was an association between SMI/FMI ratio and survival, patients with the lowest quintile SMI/FMI ratio having a significantly lower survival when compared with the highest quintile, both in the crude model and when adjusted for age, gender, and comorbidity. Additionally, FMI, radiodensity, and SMI/FMI, but not SMI, were significantly associated with Charlson comorbidity index (P < 0.01).

Conclusions

The SMI/FMI ratio may be associated with both pre-transplant comorbidity and post-transplant survival even though the significance of SMI is unclear. This suggests that SMI/FMI ratio is a better indicator of muscular impairment than skeletal muscle quantity alone. The finding may reflect the complex interplay between muscle mass, muscular fat infiltration and metabolic health, all important determinants of wellness and longevity. In summary, our study underscores the potential of the SMI/FMI ratio as a predictor of outcome after KTx, a finding possibly transferable to other patient populations.