Respiratory bronchiolitis interstitial lung disease

Respiratory bronchiolitis interstitial lung disease (RB-ILD) is a smoking related interstitial lung disease closely related to respiratory bronchiolitis, but demonstrating more severe histological, imaging and clinical findings.

Epidemiology

In all cases RB-ILD is typically associated with heavy smoking (usually of 30 pack-years or more) and is usually seen in young middle aged patients (30-40 years of age). 

Clinical presentation

Presentation tends to be with progressive shortness of breath and chronic cough ⁴. Inspiratory crackes are heard in up to half of patients. Clubbing is rare ¹.

Pathology

On lung biopsy pigment laden macrophages are found within alveoli and peribronchial inflammation noted. Unlike simple respiratory bronchiolitis, fibrosis extends beyond the tissues immediately adjacent to respiratory bronchioles and extends into alveolar septae.

Histologically RB-ILD is very similar to desquamative interstitial pneumonia (DIP) and many authors feel that the two conditions are closely related, or even variants of the same condition ³. It has even been suggested that DIP should be abolished altogether, and simply thought of as end-stage / severe RB-ILD ⁵.

Radiographic features

HRCT

Features include

• ground glass opacities
• poorly defined centrilobular nodules
• no particular distribution with both upper and lower zones potentially affected
• if advanced, fibrosis may be evident typically affecting the sub pleural regions and more so in the lower lung zones
• other changes related to smoking
  • bronchial wall thickening
  • centrilobular emphysema

Treatment and prognosis

Usually no treatment is required other than giving up smoking.

Differential diagnosis

On HRCT appearances consider

• non-specific interstitial pneumonitis (NSIP)
• desquamative interstitial pneumonia (DIP)
• acute or sub-acute hypersensitivity pneumonitis (HP)