Pathophysiology and Pathogenesis

In the developed world, cystic fibrosis (Chapter 395) is the most common cause of clinically significant bronchiectasis. Other conditions associated with bronchiectasis include primary ciliary dyskinesia, foreign body aspiration, aspiration of gastric contents, immune deficiency syndromes (especially humoral immunity), and infection, especially pertussis, measles, and tuberculosis. Bronchiectasis can also be congenital, as in Williams-Campbell syndrome, in which there is an absence of annular bronchial cartilage, and Marnier-Kuhn syndrome (congenital tracheobronchomegaly), in which there is a connective tissue disorder. Other disease entities associated with bronchiectasis are right middle lobe syndrome (chronic extrinsic compression of right middle lobe bronchus by hilar lymph nodes) and yellow nail syndrome (pleural effusion, lymphedema, discolored nails).

Three basic mechanisms are involved in the pathogenesis of bronchiectasis. Obstruction can occur because of tumor, foreign body, impacted mucus due to poor mucociliary clearance, external compression, bronchial webs, and atresia. Infections due to Bordetella pertussis, measles, rubella, togavirus, respiratory syncytial virus, adenovirus, and Mycobacterium tuberculosis induce chronic inflammation, progressive bronchial wall damage, and dilatation. Chronic inflammation similarly contributes to the mechanism by which obstruction leads to bronchiectasis. Inflammatory mediators such as neutrophil elastase, interleukin-6, interleukin-8, and tumor necrosis factor-α (TNF-α) have been found to be elevated in the airways of patients with bronchiectasis. The mechanism by which bronchiectasis occurs in congenital forms is likely related to abnormal cartilage formation. The common thread in the pathogenesis of bronchiectasis consists of difficulty clearing secretions and recurrent infections with a “vicious circle” of infection and inflammation resulting in airway injury and remodeling.