Transbronchial biopsy as a tool to evaluate small-airways disease in asthma. Cons.

Recently, there has been renewed interest in the importance of the small airways (internal perimeter v6 mm) in asthma [1]. This was initiated largely by the observation that the use of the inhaled corticosteroid beclomethasone as a small-particle formulation, with greater penetration to the peripheral lung, results in similar improvements in symptoms and lung function at half the delivered dose of standard formulations of beclomethasone [2]. The structure of the small airways is altered in asthma, even in mild cases [3], and structural changes in the small airways will theoretically lead to greater alterations in airway mechanics than similar changes in the central airways [4]. Therefore, it seems desirable to find a way to safely assess the pathology of small airways in asthma. Transbronchial biopsy (TBB) is not the way to do it, at least not yet. In this issue of the Journal, BALZAR et al. [5] have shown that small airways are present in 45% of TBB specimens from patients with severe asthma. In the same cases, the density (cells?mm) of inflammatory cells in the small airways (membranous bronchioles and smaller) seen in TBB was greater than the density in endoscopic bronchoscopic biopsies (EBB) from medium and large airways (cartilaginous bronchi) of patients with severe asthma. The authors conclude that TBB may be used to assess pathological changes in small airways in asthma. They have shown considerable endeavour in highlighting the potential of these tissue specimens for study. However, TBB should not yet be regarded as a useful tool for assessing asthma, for two reasons: 1) the significance of greater numbers of inflammatory cells?mm in the distal airway compared with central airways as a marker of a pathological process needs to be validated; and 2) the usefulness of the results does not outweigh the risks involved in obtaining them.