Post-Viral Bronchiolitis Obliterans

Post-viral bronchiolitis obliterans (also called post-infectious BO or BOOP-like illness, depending on histopathology) is a serious chronic lung disease that develops as a complication of severe viral lower respiratory tract infection. The pathophysiology involves severe acute viral injury to bronchiolar epithelium, followed by an aberrant healing response characterized by submucosal fibrosis, granulation tissue, and concentric narrowing of small airways (constrictive bronchiolitis), distinct from cryptogenic organizing pneumonia (BOOP) which has different histopathology and prognosis.

The condition is most commonly seen in children, particularly following adenovirus pneumonia (especially serotypes 3, 7, 14, 21), respiratory syncytial virus (RSV), measles, influenza, parainfluenza, and mycoplasma. Adenovirus serotype 7 is particularly notorious for causing severe necrotizing pneumonia followed by BO in children. Risk factors include young age (under 2 years), severe initial illness requiring mechanical ventilation, indigenous or genetically predisposed populations (notable cluster in Indigenous populations of South America), and prolonged hypoxemia.

Clinical presentation includes persistent or progressive cough, wheezing, exercise intolerance, recurrent respiratory infections, and chronic hypoxemia after initial viral pneumonia. Pulmonary function shows severe fixed obstruction (FEV1 often 30-50% predicted) with little or no bronchodilator response. HRCT findings include mosaic attenuation pattern (heterogeneous lung density due to air trapping), bronchiolar wall thickening, central bronchiectasis, and atelectasis. Treatment is largely supportive: bronchodilators (limited efficacy due to fixed obstruction), inhaled and systemic corticosteroids (variable response), low-dose long-term azithromycin (immunomodulatory), supplemental oxygen, pulmonary rehabilitation, prevention and treatment of recurrent infections, and lung transplantation for end-stage disease. Some children stabilize over time, while others progress.