P.92 - Magnetic resonance biomarkers in the proximal and distal upper extremity in a large cohort of boys with Duchenne muscular dystrophy

Quantitative magnetic resonance (qMR) biomarkers are increasingly being used as outcomes in clinical trials in Duchenne muscular dystrophy (DMD). However, these measures are predominantly used in the legs, partly due to a lack of natural history data using qMR biomarkers in the upper extremity. The ImagingDMD research group has been working to develop qMR biomarkers that for both nonambulatory and ambulatory boys. Here, we present results from the first year of collection of upper extremity data. Boys with DMD (n = 85, 12.0 ± 3.0 yrs, 24 nonambulatory) and unaffected control subjects (n = 24, 12.7 ± 3.1 yrs) participated in this multicenter study. Chemical shift based imaging was used to determine muscle fat fraction and multiple TE spin echo imaging was used to determine MRI-T2 in the deltoid, biceps brachii, triceps brachii, and forearm extensor and flexor muscles. Single voxel 1H-MRS was used to measure fat fraction as well as 1H2O-T2 in the biceps brachii and deltoid muscles. Boys also completed the Performance of Upper Limb (PUL) test (v. 2.0). All qMR biomarkers were significantly elevated in boys with DMD compared with unaffected boys, and all except 1H2O-T2 were significantly higher in nonambulatory compared with ambulatory boys. All qMR biomarkers were significantly correlated with total PUL score, with the strongest correlations (r > 0.70) seen in the proximal upper extremity. Total PUL score was more closely related to qMR biomarkers than age, however qMR biomarkers except 1H2O-T2 progressively increased with age. Both deltoid and biceps muscles were significantly more progressed (higher MRI-T2 and FF) than forearm extensors, and deltoid was significantly more progressed than triceps brachii. In summary, these data provide important natural history data in the upper extremity of both ambulatory and nonambulatory boys with DMD and provide an important foundation to plan clinical trials including upper extremity qMR biomarkers.