Correlation of Qualitative And Quantitative MRI Parameters for Assessment of Fatty Infiltration in Patients with Neuromuscular Diseases

Background & Purpose: The musculature of patients suffering from neuromuscular diseases (NMD) is mainly affected by atrophy/hypertrophy, fatty infiltration, and/or edematous changes [1]. Therefore, MRI is an important tool for diagnosis and monitoring. Concerning fatty infiltration, standard T1-weighted or T2-weighted DIXON TSE sequences enable a qualitative assessment of muscle involvement [2]. To achieve higher comparability semi-quantitative grading scales, such as the 4-point Mercuri scale [3], can be applied. However, the evaluation remains dependent on the reader's judgment. Therefore, effort is being invested to develop quantitative MRI techniques, such as proton density fat fraction (PDFF) mapping. The present work aims to assess the diagnostic value of PDFF mapping in correlation to Mercuri grading in patients with DM2, LGMD2A, and Pompe disease. Methods: T2-weighted DIXON TSE and PDFF mapping were performed in 13 patients (DM2: n = 5; LGMD2A: n = 5; Pompe disease: n = 3). Nine different thigh muscles were rated in all patients according to the Mercuri grading and segmented to extract PDFF values. Results: Mean PDFF values ranged from 7 to 37% in Pompe and DM2 patients and up to 79% in LGMD2A patients (Fig. 1). In all three groups a high correlation of the Mercuri grading and PDFF values was observed (Table 1). Conclusion: In the investigated patient groups PDFF mapping offers the same diagnostic value as the clinically established Mercuri grading. With its greater dynamic range (enabling the assessment of more subtle changes) and the increased objectivity, PDFF should be considered a potential biomarker and alternative to Mercuri grading in the assessment of fatty infiltration of muscle tissue.