Low adipose tissue infiltration in skeletal muscle is a protective phenotype of all-cause death in patients undergoing dialysis.

Background & Aims: A newly developed low-attenuation muscle index (LAMI) reflects the relationship of the degree of adipose tissue infiltration in low-attenuation muscle and the skeletal muscle quality on computed tomography (CT) images. We investigated the relationship between CT-derived LAMI and ratio of low-attenuation muscle area to skeletal muscle area (LAMA/SMA) at transverse process of the first lumbar vertebra (L1) and all-cause death in dialysis patients.

Methods: This retrospective cohort study of initial-dialysis patients enrolled from January 1, 2014, to June 30, 2020. The endpoint of all-cause death was recorded up to December 31, 2022. Patients were divided into low- (n = 408) and high- (n = 425) LAMI groups according to the sex-based LAMI cutoff value. Baseline clinical data, CT-derived parameters, survival rates and survival times were compared between the two groups. Restricted cubic spline was used to explore the relationships between LAMI and all-cause death separately for men and women. Multivariate Cox regression analysis and stepwise Cox regression analysis were used to analyze the association between LAMI and all-cause death.

Results: A total of 833 patients were eligible to analysis, and 536 (64.35 %) patients were male. The median follow-up time was 3.86 years (range, 0-9.11), and 225 (27.01 %) patients died during follow-up period. The low-LAMI group exhibited significantly lower low-attenuation muscle radiodensity [6.35(4.33,7.67)HU vs. 7.58(6.06,8.92)HU] and LAMA/SMA ratio [0.35(0.27,0.44) vs. 0.43(0.34, 0.51)], yet significantly greater skeletal muscle radiodensity (41.50 [7.09]HU vs. 29.60 [7.46]HU) compared to the high-LAMI group (all P < 0.001). Additionally, this group had a significantly lower incidence of all-cause death (20.3 % vs. 33.4 %) and significantly longer survival time (50.97[24.98]months vs. 44.90[23.92]months) (both P < 0.001). According to the sex-based restricted cubic spline models, linear relationships between LAMI and all-cause death were found for men and women (both nonlinear P > 0.05). Multivariate Cox regression analysis and stepwise Cox regression analysis revealed that a low LAMI and a low LAMA/SMA ratio were both independent protective factors of all-cause death in dialysis patients (all P < 0.01).

Conclusions: Adipose tissue infiltration in skeletal muscle is not always a harmful phenotype for dialysis patients, when its area is relatively localized.