168PCentiles for respiratory function in paediatric, GC-treated boys with Duchenne muscular dystrophy in London

Respiratory decline is a primary aspect of disease progression in boys with Duchenne muscular dystrophy (DMD), and along with cardiac dysfunction, is the primary cause of mortality. However, there is significant heterogeneity in the rate of progression, in particular after loss of ambulation, and this can present difficulties for clinical monitoring when discussing progression to mechanical ventilation. We present centiles for the Forced Vital Capacity (FVC), FVC percent predicted (FVCpp), and Peak Expiratory Flow (PEF) in boys between the ages of 5 and 16 years who initiated glucocorticoid steroids (GC) seen at Gt Ormond St Hospital. Plots for the 10th, 25th, 50th, 75th and 90th centiles for the FVC, FVCpp, and PEF will be presented. The cohort contained spirometry data for 241 patients, across 1414 assessments, seen at GOSH between 2007 and 2025, with a median age at first visit of 8 years (IQR: 6.2, 10.6). The FVC declined to below 1L by 14 years 10 months in patients on the 5th centile, but this threshold was not observed in those on the 10th centile or above before the age of 16 years. Patients on the 10th centile had an observed peak FVCpp below 80%, whilst patients on the 25th, 50th and 75th centiles displayed a decline to 80% FVCpp at 10 years 7 months, 12 years 6 months and 14 years 2 months respectively. Patients on the 10th and 25th centiles had an FVCpp that declined to below 50% at age 13 years 3 months and 14 years 6 months respectively, but this was not observed for patients on the 50th centile and above before 16 years. The PEF predominantly increased over time in this cohort. Centiles provide a method for contextualising respiratory trajectories, which can be otherwise difficult to understand for patients and their carers. In particular, the centiles presented provide insights into typical vs. atypical rates of respiratory decline, which is crucial for conversations around increased respiratory care such as ventilatory support.