The silent zone of paediatric asthma: integrating small airway dysfunction assessment into clinical practice.

Small airway dysfunction (SAD) is increasingly recognised as a clinically relevant component of paediatric asthma because peripheral airway abnormalities may precede spirometric impairment and contribute to poor disease control despite preserved FEV1. This narrative review summarises current evidence on the assessment and clinical implications of SAD in children, based on studies identified through PubMed/MEDLINE and the Cochrane Library. Spirometry remains the cornerstone of asthma evaluation but has limited sensitivity for early peripheral airway disease. Impulse oscillometry provides the most practical effort-independent assessment of distal airway mechanics, particularly in preschool children, while body plethysmography, multiple-breath nitrogen washout, high-resolution computed tomography, and inflammatory biomarkers including FeNO, alveolar nitric oxide, and volatile organic compounds offer complementary information in selected settings. Current evidence supports a multimodal and clinically integrated approach when symptoms and spirometry are discordant. However, standardised paediatric reference values, cost-effectiveness analyses, and randomised trials demonstrating improved outcomes with SAD-guided management are required before routine implementation in clinical guidelines.