Harvey's Garden

Bronchiolitis obliterans

2 min read

  • Submucosal fibrosis leads to concentric narrowing of the bronchiolar lumen.

  • Progressive scarring eventually results in complete closure (obliteration) of the small airways.

  • Epidemiology & Risk Factors

    • Lung Transplant: The hallmark of chronic allograft rejection (occurs months to years post-transplant; leading cause of long-term mortality). c
    • Hematopoietic Stem Cell Transplant (HSCT): Manifestation of chronic Graft-Versus-Host Disease (GVHD).
    • Toxic Inhalation: Diacetyl (“popcorn lung” in microwave popcorn factory workers), nitrogen dioxide (silo filler’s disease), sulfur mustard, chlorine gas.
    • Post-Infectious: Severe viral infections in childhood (RSV, Adenovirus) or atypical pneumonia (Mycoplasma).
    • Autoimmune: Rheumatoid Arthritis (RA).

  • Clinical Features

    • Insidious onset of progressive dyspnea on exertion (DOE).
    • Dry, nonproductive cough.
    • Wheezing and end-inspiratory squeaks/crackles on auscultation.
    • Key Feature: Symptoms are not reversible with bronchodilators.

  • Diagnosis

    • Initial/Screening: Pulmonary Function Tests (PFTs).
      • Shows a fixed obstructive pattern: ↓ FEV1, ↓ FEV1/FVC (< 70%). c
      • Negative bronchodilator response.
      • Normal DLCO (helps differentiate from emphysema).
    • Imaging:
      • CXR: Often normal or shows hyperinflation.
      • High-Resolution CT (HRCT): Test of choice. Shows mosaic attenuation (patchy areas of relative lucency), expiratory air trapping, and bronchial wall thickening.
    • Confirmatory/Gold Standard: Lung biopsy.
      • Definitive diagnosis but often unnecessary if clinical context (e.g., post-transplant) and HRCT are classic.
      • Histology: Submucosal fibroproliferation leading to concentric narrowing/obliteration of membranous and respiratory bronchioles.

  • Differential Diagnostics

    • Asthma: Diff by (+) bronchodilator reversibility on PFTs and episodic nature.
    • COPD/Emphysema: Diff by smoking hx and ↓ DLCO.
    • Bronchiectasis: Diff by chronic productive (purulent) cough, hemoptysis, and marked airway dilation/signet ring sign on HRCT.
    • Cryptogenic Organizing Pneumonia (COP/BOOP): Diff by restrictive PFT pattern, alveolar infiltrates on imaging, and rapid response to systemic corticosteroids.

  • Management

    1. Primary/Supportive: Discontinue offending exposures. Supplemental O2, symptom management (inhaled bronchodilators, cough suppressants), and pulmonary rehab.
    2. Post-Transplant/GVHD: Augment systemic immunosuppression (e.g., tacrolimus, cyclosporine, systemic steroids).
    3. Adjunctive: Macrolides (e.g., Azithromycin) often used for immunomodulatory and anti-inflammatory properties (↓ IL-8).
    4. Refractory/Definitive: Re-transplantation for severe, progressive disease.

  • Complications

    • Progressive, irreversible respiratory failure.
    • Cor pulmonale (right heart failure 2/2 pulmonary HTN).
    • Increased susceptibility to secondary respiratory infections.

Graph View