Targeting the distal lung in asthma: do inhaled corticosteroids treat all areas of inflammation?

Inflammation of the distal lung, which consists of the small airways (internal diameter <2 mm) and alveolar tissue, is an important feature of the asthma clinical syndrome comprising airway inflammation, airway hyperresponsiveness and bronchodilator-responsive expiratory airflow limitation. Support for this assertion is derived from histologic studies which have demonstrated evidence of inflammation in this anatomic compartment, along with additional studies, which have elucidated the radiologic and physiologic correlates of distal lung inflammation. Delivering inhaled drugs to this area is challenging and is dependent on a number of drug- and delivery device-related factors, as well as on a patient's inhaler technique and bronchial anatomy. Newer chlorofluorocarbon-free formulations of inhaled corticosteroids such as hydrofluoroalkane propelled metered-dose inhalers and dry powder inhalers appear to have certain advantages with regard to drug delivery that facilitate improved drug delivery to the distal lung. Mounting evidence indicates that recognition and treatment of distal lung inflammation may be key components of appropriate asthma pharmacotherapy.