Diaphragm Involvement in Duchenne Muscular Dystrophy (DMD): An MRI Study

Background: Duchenne muscular dystrophy (DMD) is characterized by progressive weakness and wasting of skeletal, cardiac, and respiratory muscles, with consequent cardiopulmonary failure as the main cause of death. Reliable outcome measures able to demonstrate specific trends over disease progression are essential. Purpose: To investigate MRI as a noninvasive imaging modality to assess diaphragm impairment in DMD. In particular, we sought to correlate MRI measurement of diaphragm structure and function with pulmonary function tests and with the abdominal volumes (VAB) measured by optoelectronic plethysmography, being an index of the action of the diaphragm. Study Type: Cross-sectional study. Population: Twenty-six DMD patients (17.9 ± 6.2 years) and 12 age-matched controls (17.8 ± 5.9 years). Field Strength/Sequence: 3-Point gradient echo Dixon sequence at 3T. Assessment: Images were acquired in breath-hold at full-expiration (EXP) and full-inspiration (INSP). INSP and EXP lung volumes were segmented and the diaphragm surface was reconstructed as the bottom surface of the left and the right lung. The inspiratory and the expiratory diaphragm surfaces were aligned by a nonrigid iterative closest point algorithm. On MRI we measured: 1) craniocaudal diaphragmatic excursion; 2) diaphragm fatty infiltration. Statistical Tests: Three-parameter sigmoid regression, one-way analysis of variance (ANOVA), Spearman's correlation. Results: In patients, diaphragm excursion decreased with age (r2 = 0.68, P < 0.0001) and fat fraction increased (r2 = 0.51, P = 0.0002). In healthy subjects, diaphragm excursion and fat fraction had no relationship with age. Diaphragm excursion decreased with decreasing FEV1 %pred (r = 0.78, P < 0.0001) and FVC %pred (r = 0.76, P < 0.0001) and correlated with VAB (r = 0.60, P = 0.0002). Fatty infiltration increased with decreasing FEV1 %pred (r = –0.88, P < 0.0001) and FVC %pred (r = –0.88, P < 0.0001). Data Conclusion: The progressive structural and functional diaphragm impairment is highly related to pulmonary function tests and to VAB. The results suggest that MRI might represent a new and noninvasive tool for the functional and structural assessment of the diaphragm. Level of Evidence: 2. Technical Efficacy: Stage 5. J. Magn. Reson. Imaging 2020;51:461–471.