Pulmonary dysfunction in children with Duchenne muscular dystrophy may occur earlier than we thought – analysis using novel methodology based on z-scores
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Department of Pulmonology and Allergology, Medical University of Gdańsk, Poland
Department of Clinical Nutrition, Medical University of Gdańsk, Poland
Department of Paediatric Cardiology and Congenital Heart Defects, Medical University of Gdańsk, Poland
Department of General Nursery, Medical University of Gdańsk, Poland
Eliza Wasilewska   

Department of Pulmonology and Allergology, Medical University of Gdańsk, Poland
Submission date: 2020-02-08
Final revision date: 2020-03-24
Acceptance date: 2020-03-26
Online publication date: 2021-03-21
Respiratory 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. Aim of the study was (1) to assess pulmonary function in DMD patients using the z-score method and (2) to identify factors affecting it, irrespective of disease progression.

Material and methods:
We 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). Information on the need of ventilation support, ambulatory status and steroid therapy was collected.

25 (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 values significantly decreased with age (r = –0.62/–0.65/–0.55; p < 0.001 respectively), after reaching the peak values in the range 9–12 or 6–9 years of age depending on the analysis method (absolute, %pv or z-score). The results fell below the normal range (z-score < –1.64) at the age of 9.8/10.4/11.6 years and below 80%pv at 10.7/12.2/13.2 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).

Analysis of the pulmonary function test based on z-scores shows that deterioration of pulmonary function in DMD males may occur earlier than we thought when measured by %pv and absolute values. Early loss of ambulation, lack of steroids and delayed steroid therapy are risk factors for worse pulmonary outcomes. To confirm these findings, cohort longitudinal studies are necessary.