“Pulmonary dysfunction in children with Duchenne muscular dystrophy may appear earlier than we thought – analysis using novel methodology based on z-scores."

Abstract

IntroductionRespiratory status is one of the main factors affecting the length of survival in patients with Duchenne muscular dystrophy (DMD) – the most common, severe, progressive muscular dystrophy.The aim: (1) to assess pulmonary function in DMD patients using the z-score method and (2) to identify factors affecting it, irrespective of the disease progress.Material and methodsWe evaluated 55 boys (aged 5 – 18 years) with DMD. The spirometry was performed with: forced vital capacity (FVC), forced expiratory volume in 1 second (FEV1), peak expiratory flow (PEF) analysis as absolute values (in litres or litres/min), % predicted value (%pv) and z-scores [z]. The need of ventilation support, ambulatory status, steroid therapy were collected.Results25(45%) subjects were non-ambulatory, 38(69%) used steroid therapy. Mean FVC[z] -2.4±2.2, FEV1[z] -2.0±1.9, PEF[z] -1.5±1.3 value significantly decrease with age (r=-0.62/-0.65/-0.55; p<0.001 respectively), after reaching the peak values between 9-12 or 6-9 years of age depending on analysis method (absolute, %pv or z-score). The results fell below normal range (z-score<-1.64) at the age of 9.8/10.4/11.6 years and below 80%pv at 10.7/13.2/13.2 for FVC/FEV1/PEF, respectively. The pulmonary function test results were significantly lower in non-ambulant (p<0.001) and non-steroid patients (p<0.02).ConclusionsAnalysis of pulmonary function test based on z-score shows that deterioration of pulmonary function in DMD males may appear earlier than we thought measured by %pv and absolute values. Early loss of ambulation, lack of or delayed steroid therapy are risk factors for worse pulmonary outcomes. To confirm these findings cohort longitudinal studies are necessary.