• Omar S Usmani, Dave Singh, Monica Spinola, Andrea Bizzi, and Peter J Barnes.
• Airway Disease Section, National Heart and Lung Institute, Imperial College London, Royal Brompton Hospital, London, UK. Electronic address: o.usmani@imperial.ac.uk.
• Respir Med. 2016 Jul 1; 116: 19-27.

BackgroundSmall airways dysfunction and inflammation contribute significantly to the clinical impact of asthma, yet conventional methods of assessing airways function in the clinic cannot reliably evaluate its presence. However, most recently, promising methods of assessment are being utilised.MethodsWe conducted a systematic literature review, using PubMed, with the aim of determining the prevalence of small airways disease in adult patients with asthma. We ascertained how small airways disease prevalence compared between different studies when measured using distinct techniques of small airways assessment.ResultsFifteen publications were identified determining the prevalence of small airways disease in asthma. Methods of assessments included impulse oscillometry, spirometry, body plethysmography, multiple-breath nitrogen washout, and high-resolution computed tomography. These studies used differing inclusion characteristics and recruited patients with a broad range of asthma severity, yet collectively they reported an overall prevalence of small airways disease of 50-60%. Small airways disease was present across all asthma severities, with evidence of distal airway disease even in the absence of proximal airway obstruction.ConclusionsSmall airways disease is highly prevalent in asthma, even in patients with milder disease. Given the clinical impact of small airways disease, its presence should not be underestimated or overlooked as part of the daily management of patients with asthma.Copyright © 2016 The Authors. Published by Elsevier Ltd.. All rights reserved.

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