[Bronchiectasis in adults: Etiological diagnosis]

Bronchiectasis is defined by a permanent and irreversible increase in airway caliber. Computed tomography (CT) scan is required for diagnosis and allows differentiating localized (affecting only one lobe) from diffuse (affecting two or more lobes) bronchiectasis. Localized bronchiectasis is usually related to a local cause (e.g., tumor, compression by lymph nodes, foreign body) whereas there are multiple causes of diffuse bronchiectasis. Main causes of diffuse bronchiectasis can be grouped into 5 categories: (1) immune deficiencies; (2) genetic disorders responsible for abnormal mucociliairy clearance (e.g., cystic fibrosis and primary ciliary dyskinesia); (3) autoinflammatory and connective tissue diseases (e.g., rheumatoid arthritis, Sjogren syndrome); (4) chronic airway inflammatory disorders (e.g., allergic broncho-pulmonary aspergillosis) or chronic infections (e.g., by nontuberculous mycobacteria) and; (5) sequelae of pulmonary insults (e.g., infection, radiotherapy). In the absence of a specific cause, bronchiectasis are called idiopathic. Bronchoscopy is the cornerstone for etiological diagnosis in localized bronchiectasis. Investigation of diffuse bronchiectasis includes standardized biological tests, eventually completed by specialized explorations (e.g., analysis of epithelial ion transport and/or ciliary beating). After this systematic approach, an etiological diagnosis is obtained in approximately 60% of cases, often resulting in therapeutic consequences and in some cases in genetic counselling.