This study describes longitudinal changes in pulmonary function measures in Duchenne muscular dystrophy (DMD) patients treated with glucocorticoids (GCs) > 1 year compared to GC naïve patients in the Cooperative International Research Group Duchenne Natural History Study, a multicenter prospective cohort study. Over a period up to 10 years 397 participants underwent 2799 pulmonary function assessments: 53 GC naïve participants (< 1 month exposure) were compared to 322 subjects with > 1 year cumulative GC treatment. Forced vital capacity (FVC), peak expiratory flow rate (PEFr), maximal inspiratory and expiratory pressures were performed and calculated as a percent predicted (%p). GC treatment slowed the rate of pulmonary decline as measured by FVC%p, in patients aged 7-9.9 years. GC treatment slowed 12 and 24-month progression of percent predicted spirometry to a greater degree in those with baseline FVC%p from < 80-34%. GC treatment resulted in higher peak absolute FVC and PEFr values with later onset of decline. Progression to an absolute FVC < 1 liter was delayed by GC treatment. Patients who reached a FVC below 1 L were 4.1 times more likely to die (p = 0.017).
