Selection Approach to Identify the Optimal Biomarker Using Quantitative Muscle MRI and Functional Assessments in Becker Muscular Dystrophy
Objective:To identify the best quantitative fat-water MRI biomarker for disease progression of leg muscles in Becker muscular dystrophy (BMD) by applying a stepwise approach based on standardized response mean (SRM) over 24 months, correlations with baseline ambulatory tests and reproducibility.Methods:Dixon fat-water imaging was performed at baseline (n=24) and 24 months (n=20). Fat fractions (FF) were calculated for three center slices and the whole muscles for 19 muscles and six muscle groups. Contractile cross sectional area (cCSA) was obtained from the center slice. Functional assessments included knee extension and flexion force, and three ambulatory tests (North Star Ambulatory Assessment (NSAA), 10-meter run, six-minute walking test). MR parameters were selected using SRM (≥0.8) and correlation with all ambulatory tests (rho≤-0.8). Parameters were evaluated based on intraclass correlation coefficient (ICC) and standard deviation (SD) of the difference. Sample sizes (SS) were calculated assuming 50% reduction in disease progression over 24 months in a clinical trial with 1:1 randomization.Results:Median whole muscle FF increased between 0.2-2.6% without consistent cCSA changes. High SRMs and strong functional correlations were found for eight FF but no cCSA parameters. All parameters showed excellent ICC (≥0.999) and similar SD of the inter-rater difference. Whole thigh three center slices FF was the best biomarker (SRM=1.04, correlations rho≤-0.81, ICC=1.00, SD=0.23%, SS=59) based on low SD and acquisition and analysis time.Conclusion:In BMD, median FF of all muscles increased over 24 months. Whole thigh three center slices FF reduced the SS by approximately 40% compared to NSAA.