TABLE 1

Aetiologies of bronchiectasis

Category	Cause/notes	Clinical phenotype	Specific treatment
Post-infection	Viral, bacterial, fungal, mycobacteria (usually classified separately)	Past history of severe infection; classically unilobar bronchiectasis	No specific treatment
NTM	M. avium and M. abscessus most frequent	Middle-aged or elderly; females with low BMI; middle lobe and lingual nodular bronchiectasis; cavitation; tree-in-bud	Antibiotic treatment
Post-TB	M. tuberculosis	Upper lobe most frequently	No specific therapy
ABPA	Hypersensitivity to A. fumigatus	History of asthma (not universal); thick sputum; S. aureus in sputum; central bronchiectasis; fleeting infiltrates	Steroids±antifungals
COPD	Smoking, biomass exposure	Fixed airflow obstruction; smoking history; bilateral lower lobe; tubular bronchiectasis	No specific therapy
Asthma	Not universally accepted as a cause of bronchiectasis	Long history of asthma; frequent exacerbations; neutrophilic airway inflammation	Inhaled corticosteroids, biologics e.g. anti-IgE and anti-IL5
Aspiration/inhalation	Foreign body aspiration, gastric contents aspiration, inhalation of corrosive substances	Lower lobe bronchiectasis	Speech and language therapy, fundoplication, removal of exacerbating drugs
Obstruction	Benign tumours, enlarged lymph nodes	Single lobe bronchiectasis	Removal of obstruction via bronchoscopy or thoracic surgery
Congenital defects of large airways	Marfan syndrome, Mounier-Kuhn syndrome (tracheobronchomegaly), Williams–Campbell syndrome (bronchial cartilage deficiency)	Specific features depending on the congenital defect	Dependant on the underlying disorder
AATD	Unopposed protease activity	Combined emphysema and bronchiectasis	Augmentation therapy is available in some countries
Yellow nail syndrome	Lymphatic obstruction	Dystrophic nails, pleural effusions, rhinosinusitis	Local treatment for nails e.g. vitamin-E, management of lymphoedema
Immunological defects	Primary: common variable immune deficiency, agammaglobulinemia, hyper-IgE syndrome; secondary: chemotherapy, immunosuppressant therapy, malignancy, HIV/AIDS	Varied clinical pattern depending on the underlying cause; patient may give a history of non-respiratory infections	Ig replacement, prophylactic antibiotics, treatment of underlying disorder, removal of iatrogenic immunosuppression
Young's syndrome	Cause not known	Bronchiectasis, rhinosinusitis and reduced fertility	See ciliary disorders below
PCD	Genetic	Middle lobe and lower lobe bronchiectasis; rhinosinusitis; middle ear infections; situs inversus in some cases	Recognition and treatment of associated problems (including rhinosinusitis, middle ear disease, infertility, ectopic pregnancy), genetic counselling, intensive airway clearance
Systemic inflammatory disease	Rheumatoid arthritis, sarcoidosis, systemic lupus erythematosus, Sjögren syndrome	Varied clinical pattern, often rapidly progressive	No specific treatment
Inflammatory bowel disease	Ulcerative colitis, Crohn's syndrome, coeliac disease	Varied clinical pattern often high sputum volumes and steroid responsive	Inhaled and systematic corticosteroids, treatment of the underlying condition
Adult CF	CFTR mutations	Upper lobe bronchiectasis; P. aeruginosa or S. aureus in sputum; non-respiratory manifestations	Specialist multidisciplinary care in adult CF centres, recognition and treatment of non-respiratory manifestations, CFTR modulator/corrector therapy
Diffuse panbronchiolitis	Idiopathic inflammatory disease	Mostly patients of Far Eastern ethnic origin	Macrolide antibiotics

NTM: nontuberculous mycobacteria; TB: tuberculosis; ABPA: allergic bronchopulmonary aspergillosis; COPD: chronic obstructive pulmonary disease; AATD: α₁-antitrypsin deficiency; PCD: primary ciliary dyskinesia; CF: cystic fibrosis; M. avium: Mycobacterium avium; M. abscessus: Mycobacterium abscessus; M. tuberculosis: Mycobacterium tuberculosis; A. fumigatus: Aspergillus fumigatus; S. aureus: Staphylococcus aureus; BMI: body mass index; Ig: immunoglobulin; IL: interleukin; CFTR: cystic fibrosis transmembrane conductance regulator; P. aeruginosa: Pseudomonas aeruginosa.