Obliterative bronchiolitis

Obliterative bronchiolitis, 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. Obliterative bronchiolitis should not be confused with cryptogenic organising pneumonia (COP), previously termed bronchiolitis obliterans organising pneumonia (BOOP). 

Epidemiology

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

• certain chemical compounds, e.g. flavouring-related lung disease

• as a complication following lung transplantation: post lung transplant bronchiolitis obliterans ²; can occur in up to 10% of patients, usually within 6-12 months following bone marrow transplantation ¹⁰

• Swyer-James syndrome ¹³

Clinical presentation

Its cardinal features are progressive breathlessness and a dry cough ¹⁴.

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 a number of causes:

• idiopathic/cryptogenic

• post-infectious

  • post-viral (e.g. adenovirus)

  • post-atypical infection (e.g. Mycoplasma pneumonia)

• noxious fume inhalation

  • "popcorn lung":  workers of a microwave popcorn plant who had inhaled diacetyl, a chemical used for flavouring, developed obliterative bronchiolitis; the term has since become a colloquial synonym for obliterative bronchiolitis

• neuroendocrine hyperplasia (pulmonary tumourlets) ⁴

• post-transplant patients

  • heart/lung transplants ³

    • representing the obstructive form of chronic lung allograft dysfunction (CLAD)

  • haematopoietic stem cell transplants ⁷ 

A helpful mnemonic is CRITTS.

Radiographic features

Plain radiograph

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

• hyperinflation

• attenuation of vascular markings

• occasionally reticular/reticulonodular markings

CT

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

• bronchiectasis

• bronchial wall thickening ⁶

• ground glass opacities ⁶

History and etymology

It was first described by the French physician 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

  • long lines reflecting limited thickened interlobular septa were significantly more frequent in patients with panlobular emphysema¹⁶

• pulmonary hypertension

  • pulmonary trunk enlargement