G.P.128: Upper limb muscle MRI fat–water quantification and clinical functional correlation in non-ambulant Duchenne muscular dystrophy

Abstract

Outcome measures in Duchenne muscular dystrophy (DMD) currently rely on invasive or functional but not very sensitive tests. Muscle MRI could offer a valuable alternative. A reliable evaluation of the upper limb could permit inclusion of non-ambulant DMD individuals not able to perform functional tests such as the 6-min walk test. 16 DMD boys and 10 age gender and age matched controls were included in this on-going study. Fat–water quantification was used to compare fat-infiltration in the forearm muscles of non-ambulant DMD patients and healthy controls. DMD individuals underwent 3T 3-point Dixon imaging of the dominant forearm to measure muscle fat-fraction (f.f.). Ten forearm muscles were segmented and mean f.f. and cross-sectional area recorded. Patients also underwent physiotherapy evaluation: Performance of Upper Limb (PUL) module; wrist extension myometry; and EK2 performance of tasks in daily life interview. Time to loss of ambulation (LOA) was recorded. To date, 8 non-ambulant DMD patients (mean age: 13.6 years; mean duration of non-ambulation 20 months) and 10 volunteers (mean age:14.6 years) have been imaged. Overall mean f.f (±SD) in DMD was significantly higher than healthy controls: (13.4 ± 11% vs 0.8 ± 0.1%, p = 0.002). Total mean area was reduced in DMD (1735 ± 331 mm2) compared to healthy controls (2398 ± 821 mm2, p = 0.04). Overall f.f. correlated with LOA (Spearman r = 0.8, p = 0.02) and wrist extension myometry (r = 0.8, p = 0.004) and less strongly with PUL (r = −0.6, p = 0.09) and with EK2 (r = 0.6, p = 0.09). Final analysis will include longitudinal change at one-year follow up. Initial results support MRI fat quantification as a potential objective biomarker to monitor disease progression in the upper limb in DMD, showing significant correlation between putative MRI pathological indices and clinically meaningful endpoints.