Development and Validation of a Nomogram for Identifying Low Appendicular Muscle Mass in Patients With Nonalcoholic Fatty Liver Disease: A Cross-Sectional Study

Background: Low appendicular muscle mass is a component of sarcopenia that can be measured using dualenergy X-ray absorptiometry.This study developed and internally validated a nomogram for identifying prevalent low appendicular muscle mass in adults with nonalcoholic fatty liver disease (NAFLD).Methods: We analyzed 1,571 participants aged 18-59 years from the National Health and Nutrition Examination Survey (NHANES) 2011-2018, randomly divided into training (n = 1,099) and testing (n = 472) sets.Low appendicular muscle mass was defined using sex-specific thresholds for appendicular skeletal muscle mass divided by body mass index (BMI).Least absolute shrinkage and selection operator (LASSO) and logistic regression were used for model development.Discrimination, calibration, decision curves, 1,000 bootstrap resamples, and comparisons with simpler models were evaluated.Prediction modeling and performance assessment were unweighted.Results: The model included age, race/ethnicity, BMI, height, triglycerides, phosphorus, and chloride.The area under the receiver operating characteristic curve (AUC) was 0.838 (95% CI: 0.808-0.868) in training and 0.812 (95% CI: 0.757-0.868) in testing.The optimism-corrected training AUC was 0.826.At a trainingderived probability cut-off of 0.1838, testing sensitivity and specificity were 65.28% and 78.25%.The testing calibration intercept and slope were 0.0010 and 0.9725.Adding laboratory variables to age, race/ethnicity, BMI, and height did not improve testing discrimination (AUC: 0.812 versus 0.813; DeLong p = 0.947).Decision-curve differences varied by threshold probability.Conclusions: The nomogram showed internal discrimination for prevalent low appendicular muscle mass in selected adults with NAFLD.Interpretation is limited by the structural relationship between anthropometric predictors and the BMI-adjusted outcome.Incremental benefit from the laboratory variables was not established in the testing set.External and prospective clinical validation are required before implementation.