Obliterative bronchiolitis

Obliterative bronchiolitis (OB),also known as bronchiolitis obliterans or constrictive bronchiolitis,Bronchiolitis Obliterans is a typedisorder that causes the airways of bronchiolitisthe lung to become inflamed, swollen and refersscarred, leading to bronchiolar inflammation with submucosal peribronchial fibrosis associated with luminal stenosis and occlusions. Obliterativepartial or complete blockage.

Terminology:

The disease is sometimes referred to as obliterative bronchiolitis or BO.

It should not be confused with bronchiolitis obliterans organising pneumoniaBronchiolitis 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

• 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 conditionexact pathophysiology of Bronchiolitis Obliterans is not fully understood, but it is believed to be a result of a complex interplay between immune and inflammatory responses, and exposure to inhaled irritants. In response to inhaled irritants, the bronchioles become inflamed and scarred, leading to partial or complete airway obstruction.

Gross anatomical pathology: On gross pathological examination, the lungs of patients with Bronchiolitis Obliterans can appear hyperinflated with decreased lung markings and increased lung markings, indicative of air trapping and airway obstruction.

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

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 isCRITTS.

Radiographic features

Plain radiograph

Chest radiographic findingsX-rays in patients with Bronchiolitis Obliterans can show hyperinflation, flattened diaphragms, flattened lung markings and decreased lung markings, indicative of air trapping and airway obstruction.

Ultrasound Exam:

• Not typically used in the diagnosis of BO.

CT

CT and HRCT scans can be normal or, if abnormal, non-specific. Some associated features include:

• hyperinflation

• attenuationused to confirm the diagnosis of vascular markingsBronchiolitis Obliterans, and can show characteristic findings of air trapping and airway obstruction, such as peripheral bullae, small airways dilatation, and parenchymal thickening.

• 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

Consider:

• asthma 

• panlobular emphysema: e.g. alpha-1-antitrypsin deficiency

  • usually has a lower lung zone predominance

• pulmonary hypertension

  • pulmonary trunk enlargement