Bronchiolitis is characterized by inflammatory injury of the small airways with interstitial sparing. Injury is nonspecific and can be caused by infections, irritants, toxic fumes, drug exposures, pneumonitides, connective tissue disorders, vasculitides, or in some cases remains idiopathic. Acute bronchitis due to infection or toxic inhalation is rare in adults and more commonly occurs in children.

Bronchiolitis should be suspected in an adult of any age with insidious onset (weeks to months) of nonproductive cough and dyspnea. High-resolution CT scan (HRCT) is the radiographic study of choice for diagnosis, although lung biopsy may be required in some cases. Treatment options are usually aimed at controlling symptoms, and care is often coordinated with a pulmonologist.

Etiologies include bronchiolitis obliterans or bronchiolitis obliterans syndrome, constrictive bronchiolitis, proliferative bronchiolitis, and cellular bronchiolitis.