Targeting small airways in asthma: the new challenge of inhaled corticosteroid treatment

Abstract

The small airways have long been considered to be important in asthma. The presence of inflammation in small airways has been well established in studies of post mortem tissue 1. Inflammation even extends to peribronchial tissues seen in transbronchial biopsy studies 2. In this issue of the European Respiratory Journal , the study by Cohen et al. 3 underscores the increasing interest in targeting treatment to the small airways with currently available fine-particle aerosols with median diameters of ∼1 μm. The study also highlights the as yet unproven potential of aerosol treatment in targeting the small airways and the complexities of such research. Cohen et al. 3 found that 5 weeks of ciclesonide treatment, a small-particle inhaled corticosteroid, improved alveolar exhaled nitric oxide, airway hyperresponsiveness and spirometry but not closing volume. They also found that the expiratory lung volume measured using high-resolution computed tomography (HRCT), after methacholine challenge, was smaller in the ciclesonide-treated group compared with the placebo group. However, the question as to whether ciclesonide is better than larger-particle aerosols for treating small airways in asthma remains unanswered. Establishing the clinical significance of small airways disease is a priority if advances in asthma management are to occur; however, this has been difficult because of the challenges in measurement. Assessment of small airways continues to be a complex undertaking and includes techniques such as transbronchial biopsy, gas washout tests 4, 5, frequency dependence of compliance, intrabronchial pressure measurements 6, forced oscillation technique (FOT) …