Obliterative bronchiolitis

Obliterative bronchiolitis (OB),also known as bronchiolitis obliterans or constrictive bronchiolitis, is a type of bronchiolitis and refers to bronchiolar inflammation with submucosal peribronchial fibrosis associated with luminal stenosis and occlusions. OB should not be confused with bronchiolitis obliterans organising pneumonia (BOOP). 

Pathology

The condition is characterised by concentric luminal narrowing of the membranous and respiratory bronchioles as a result of submucosal and peribronchiolar inflammation and fibrosis without any intraluminal granulation tissue or polyps/polyposis. There is an absence of diffuse parenchymal inflammation.

Aetiology

It can result from number of causes:

• idiopathic/cryptogenic
• post-infectious
  • post viral 
  • post atypical infection (e.g. Mycoplasma pneumonia)
• noxious fume inhalation
• neuroendocrine hyperplasia (pulmonary tumourlets) ⁴
• post-transplant patients
  • heart/lung transplants ³
  • haematopoietic stem cell transplants ⁷ 

Mnemonic: CRITTS

Associations

Recognised associations include:

• inflammatory bowel disease
• rheumatoid arthritis: considered the commonest connective tissue disease to be associated with obliterative bronchiolitis ^11,12
• medications, e.g. penicillamine
• as a complication following lung transplantation: post lung transplant bronchiolitis obliterans ²
• as a complication following bone marrow transplantation: can; can occur in up to 10% of patients, usually within 6-12 months following bone marrow transplantation ¹⁰
• Swyer-James syndrome ¹³

Radiographic features

Plain radiograph

Chest radiographic findings can be normal or, if abnormal, nonspecific. Some associated features include:

• hyperinflation
• attenuation of vascular markings
• occasionally reticular or reticulonodular markings

CT

On HRCT chest, there are often sharply defined, areas of decreased lung attenuation associated with vessels of decreased calibre. These changes represent a combination of air trapping and oligaemia. This combination can give a mosaic attenuation pattern. Other features include:

• bronchial dilatation
• bronchial wall thickening ⁶
• ground glass opacities ⁶

History and etymology

It was first described by A.C.Reynaud in 1835 ^8-9 .

Differential diagnosis

• asthma 
• panlobular emphysema: e.g. alpha-1-antitrypsin deficiency
  • usually has a lower lung zone predominance
• pulmonary hypertension
  • pulmonary trunk enlargement