Over the last 10 to 15 years, the emerging role of distal or small-airway inflammation in the pathogenesis of asthma has been increasingly recognized. This review attempts to focus on the importance of small-airway dysfunction in asthma. Pathologic changes seen in the distal airways were highlighted using data obtained from biopsy studies, as well as changes seen in fatal asthma. Advances in the diagnostic evaluation of the distal airways were reviewed, specifically pulmonary function tests (including exhaled nitric oxide and impulse oscillometry), and newer imaging techniques. Finally, studies that have led to advances in therapeutic treatment of the small airways in childhood asthma were highlighted. The terms distal airways and small airways are used interchangeably throughout the article.
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