Objective:To investigate the relationship between intramuscular adipose tissue index (IATI) calculated from computed tomography images at transverse process of the first lumbar and all-cause mortality in maintenance dialysis patients, and to provide a reference for improving the prognosis in these patients.Methods:It was a multicenter retrospective cohort study. The clinical data of patients who received maintenance hemodialysis or peritoneal dialysis treatment from January 1, 2017 to December 31, 2019 in 4 grade Ⅲ hospitals including Zhongda Hospital Affiliated to Southeast University, Taizhou People's Hospital Affiliated to Nanjing Medical University, Affiliated Hospital of Yangzhou University, and the Third Affiliated Hospital of Soochow University were retrospectively collected. IATI was calculated by low attenuation muscle (LAM) density/skeletal muscle density. The receiver-operating characteristic curve was used to determine the optimal cut-off value of IATI, and the patients were divided into high IATI group and low IATI group according to the optimal cut-off value. The differences of baseline clinical data and measurement parameters of the first lumbar level between the two groups were compared. The follow-up ended on December 23, 2022. The endpoint event was defined as all-cause mortality within 3 years. Kaplan-Meier survival curve and log-rank test were used to analyze the survival rates and the differences between the two groups. Multivariate Cox regression analysis models were used to analyze the association between IATI and the risk of all-cause mortality in maintenance dialysis patients. Multivariate logistic regression analysis model was used to analyze the influencing factors of high IATI.Results:A total of 478 patients were eligibly recruited in this study, with age of (53.55±13.19) years old and 319 (66.7%) males, including 365 (76.4%) hemodialysis patients and 113 (23.6%) peritoneal dialysis patients. There were 376 (78.7%) patients in low IATI (<0.42) group and 102 (21.3%) patients in high IATI (≥0.42) group. The proportion of age ≥ 60 years old ( χ2=24.746, P<0.001), proportion of diabetes mellitus ( χ2=5.570, P=0.018), fasting blood glucose ( t=-2.145, P=0.032), LAM density ( t=-3.735, P<0.001), LAM index ( t=-7.072, P<0.001), and LAM area/skeletal muscle area ratio ( Z=-9.630, P<0.001) in high IATI group were all higher than those in low IATI group, while proportion of males ( χ2=11.116, P<0.001), serum albumin ( Z=2.708, P=0.007) and skeletal muscle density ( t=12.380, P<0.001) were lower than those in low IATI group. Kaplan-Meier survival analysis showed that the 3-years overall survival rate of low IATI group was significantly higher than that in high IATI group (Log-rank χ2=19.188, P<0.001). Multivariate Cox regression analysis showed that IATI<0.42 [<0.42/≥0.42, HR(95% CI): 0.50 (0.31-0.83), P=0.007] was an independent protective factor of all-cause mortality, and age ≥60 years old [ HR (95% CI): 2.61 (1.60-4.23), P<0.001], diabetes mellitus [ HR (95% CI): 1.71 (1.06-2.78), P=0.029] and high blood neutrophil/lymphocyte ratio [ HR (95% CI): 1.04 (1.00-1.07), P=0.049] were the independent risk factors of all-cause mortality in maintenance dialysis patients. Stepwise Cox regression analysis showed that IATI<0.42 was still an independent protective factor of all-cause mortality in maintenance dialysis patients [<0.42/≥0.42, HR (95% CI): 0.45 (0.27-0.76), P=0.003]. Multivariate logistic regression analysis showed that low skeletal muscle density [ OR (95% CI): 0.84 (0.81-0.88), P<0.001] and high serum triglyceride [ OR (95% CI): 1.39 (1.07-1.82), P=0.015] were the independent influencing factors of IATI≥0.42. Conclusion:IATI<0.42 of the first lumbar level is an independent protective factor of all-cause mortality in maintenance dialysis patients. Localized myosteatosis within high-quality skeletal muscle may reduce the risk of all-cause mortality in these patients.