[Small airway disease: facts or fiction?]

The term "small airways" has come to mean airways of less than 2 mm internal diameter, i.e. small bronchi and especially bronchioles. Since disturbed function and inflammation of the small airways is present in most airway and lung diseases and is regarded as an early stage of chronic airflow obstruction, the term "small airways disease" was coined. The newly created clinical entity and the hypothesis were criticized from the beginning, and this scepticism is strongly supported by new concerning the accuracy or validity of tests of small airways function on the one hand, and functional, morphological and prospective epidemiological investigations on the other. The use of the term "small airways disease" is doubtful when accompanying a well-defined pulmonary disease, and is inferior to the precise term "bronchiolitis" when present as an isolated disease of the bronchioles. Ultimately, it is still unproven that inflammation of "small airways" at an early stage leads to chronic airflow obstruction, i.e. emphysema.