673P Magnetization transfer imaging in late-onset Pompe disease.

Magnetization transfer imaging (MTI) evaluates the exchange of magnetization between protons in free water molecules and protons bound to macromolecules, including lipids. Widely used in the study of central nervous system diseases, its application in the neuromuscular field has been previously explored only in a Spanish cohort of patients with late-onset Pompe disease (LOPD). To investigate the potential role of MTR as an early biomarker of muscle involvement, we here evaluate magnetization transfer ratio (MTR) and fat fraction (FF) in patients with LOPD in various stages of disease compared to healthy controls (HCs). Quantitative muscle MRI (qMRI) was performed on 31 LOPD patients (21 with mild and 10 with moderate/severe clinical involvement) and 31 matched HCs using 3T MRI. FF and MTR were measured in 11 thigh muscles. Correlations between FF and MTR were assessed. Additionally, FF and MTR were compared between groups of HCs vs. early vs. moderate/severe LOPD. We also explored whether MTR can detect muscle involvement in not yet fat-infiltrated muscles (FF ≤ 10%) in early LOPD. MTR of thigh muscles with FF ≤ 10% was significantly lower in LOPD compared to HCs. Changes in MTR could be detected even in mildly symptomatic patients, particularly in the medial and posterior compartments (Mann-Whitney U: p < 0.05). MTR and FF were inversely correlated in all subjects groups. We found significant differences in MTR and FF changes at the group level between mild and moderate/severe vs HCs. We conclude that MTI has potentially high sensitivity to detect mild muscle fiber damage, even before fat replacement has occurred, making it a useful biomarker to monitor early signs of disease, disease progression, and the efficacy of treatment approaches (Sanofi company provided support for this study, but had no role in study design, data collection and analysis, decision to publish, or preparation of the abstract). (The first and second authors contributed equally to this work) [ABSTRACT FROM AUTHOR]