Increased Airway Smooth Muscle Mass in Children with Asthma, Cystic Fibrosis, and Non-Cystic Fibrosis Bronchiectasis

Rationale: Structural alterations to airway smooth muscle (ASM) are a feature of asthma and cystic fibrosis (CF) in adults.Objectives: We investigated whether increase in ASM mass is already present in children with chronic inflammatory lung disease.Methods: Fiberoptic bronchoscopy was performed in 78 children (median age [IQR], 11.3 [8.5–13.8] yr): 24 with asthma, 27 with CF, 16 with non-CF bronchiectasis (BX), and 11 control children without lower respiratory tract disease. Endobronchial biopsy ASM content and myocyte number and size were quantified using stereology.Measurements and Main Results: The median (IQR) volume fraction of subepithelial tissue occupied by ASM was increased in the children with asthma (0.27 [0.12–0.49]; P < 0.0001), CF (0.12 [0.06–0.21]; P < 0.01), and BX (0.16 [0.04–0.21]; P < 0.01) compared with control subjects (0.04 [0.02–0.05]). ASM content was related to bronchodilator responsiveness in the asthmatic group (r = 0.66, P < 0.01). Median (IQR) myocyte number (cells per mm2 of...