Synopsis
Recognise small-airway physiology and constrictive bronchiolitis, identify causal contexts including transplantation and inhalation injury, and coordinate evidence-limited specialist treatment without confusing organising pneumonia.
- Small airways are bronchioles below the resolution of routine imaging; substantial disease can exist before conventional spirometry becomes clearly abnormal.
- Bronchiolitis obliterans, or constrictive bronchiolitis, is fibrotic narrowing and obliteration of small airways that usually produces progressive, relatively fixed airflow obstruction.
- Important contexts include lung transplantation, allogeneic haematopoietic stem-cell transplantation, connective-tissue disease, severe inhalational injury, selected infections and drug or immune-mediated injury.
Key red flags
A sustained fall from the best post-transplant expiratory function with new obstruction may represent BOS, but transplant specialists must exclude infection, acute rejection, airway stenosis and restrictive allograft dysfunction.
Investigation priorities
Confirm obstruction, trajectory and degree of reversibility.
Management branches
Progressive breathlessness or cough accompanies unexplained fixed obstruction or expiratory air trapping.
- Construct a timeline of transplantation, infection, inhalational exposure, autoimmune disease and medicines, noting onset relative to each potential insult.
- Repeat quality-assured spirometry with bronchodilator and obtain volumes, gas transfer and paired inspiratory-expiratory CT where clinically justified.
Key medicines
Azithromycin for selected post-lung-transplant BOSA BTS-supported specialist regimen is 250 mg orally three times weekly for prevention, or 250 mg on alternate days for a defined treatment trial.
Inhaled long-acting bronchodilator trialUse one locally selected licensed inhaler at its device-specific adult maintenance dose after observing technique and documenting a baseline endpoint.