Summer SS, Wong BL, Rutter MM, et al. - In the present study, the researchers sought to investigate age-related changes in appendicular lean mass (ALM) and ALM index in males with glucocorticoid-treated Duchenne muscular dystrophy (DMD) compared with controls. This chart review involved longitudinal data on 499 males with DMD receiving glucocorticoids and 693 controls, ages 5 to 22.9 y. Males with DMD had lower ALM from an early age compared with controls. Males with DMD have a gradual decrease in lean mass with age and a deterioration of functional mobility. Dual energy x‐ray absorptiometry measurement of ALM can be useful for lean mass status monitoring in DMD patients, providing important information for individual treatment plans and research efforts.