Bronchiolitis Obliterans in Children
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Direct answer
When a child remains tachypnoeic, hypoxaemic and crackly for months after a severe lower respiratory infection — most often adenovirus, the dominant cause of post-infectious bronchiolitis obliterans in India — the diagnosis to hold is bronchiolitis obliterans: fibrotic obliteration of the small airways producing irreversible airflow obstruction that bronchodilators cannot reverse. The clinical signature is persistent tachypnoea, exercise limitation, crackles and hypoxaemia for more than 60 days after the inciting illness, in a child who does not wheeze his way out of trouble the way an asthmatic does. High-resolution computed tomography clinches it with a mosaic attenuation pattern — dark, air-trapped lobules beside dense perfused ones — along with bronchiectasis and airway wall thickening on expiration. No therapy reverses the fibrosis; care is supportive (supplemental oxygen, nutrition, immunisation, airway clearance, treatment of intercurrent infection), with macrolides and systemic or inhaled corticosteroids tried without strong evidence, and lung transplantation as the endgame.
What you must remember
- Definition threshold: persistent respiratory symptoms and signs for at least 60 days after a lower respiratory infection — the duration clause separates post-infectious bronchiolitis obliterans from ordinary bronchiolitis, which resolves in one to two weeks.
- Cause ladder: adenovirus (types 3, 7 and 21 especially) is the leading cause in Indian series, followed by measles, influenza, mycoplasma and Bordetella pertussis; a severe adenoviral pneumonia in a toddler is the classic setup.
- Physiology: concentric fibrosis of the terminal and respiratory bronchioles causes one-way obstruction — air enters but cannot leave — producing air trapping, hyperinflation and depressed diaphragms on radiograph.
- HRCT signature: mosaic perfusion (geographic areas of differing density), air trapping on expiratory sequences, bronchiectasis and bronchial wall thickening; the lucent, small unilateral lung with air trapping and small pulmonary artery constitutes Swyer-James-McLeod syndrome, the unilateral variant following childhood infection.
- Differentiators from asthma: absent or poor bronchodilator response, persistent crackles, hypoxaemia disproportionate to symptoms, and no atopic diurnal variability; pulmonary function shows fixed obstruction without significant reversibility (in cooperative children).
- Management honesty: no proven disease-modifying therapy — corticosteroids, azithromycin and montelukast are empirical; the evidence-backed pillars are oxygen, nutrition, vaccines, airway clearance and prompt treatment of exacerbations.
- Course: most survivors improve slowly over years, though many retain exercise limitation and bronchiectasis; a minority progress to respiratory failure and become transplant candidates.
- Look-alikes to exclude: cystic fibrosis (always consider in an Indian child with recurrent chest disease), aspiration, congenital malformations, immunodeficiency and tuberculosis.
Working through the six-month follow-up
Consider a two-year-old discharged after three weeks of ventilated adenoviral pneumonia, now six months on: respiratory rate 55 at rest, saturation dipping to 86 per cent on playing, hyperinflated chest with early clubbing and bilateral coarse crackles that never cleared. First, widen the differential before committing: sweat chloride or genetic testing for cystic fibrosis, immunoglobulins, tuberculin testing where plausible, and a feed review for aspiration. Second, image: the radiograph shows hyperinflation with asymmetric lucency; high-resolution CT with expiratory views delivers the verdict — mosaic attenuation, bronchial wall thickening and early cylindrical bronchiectasis. Third, document severity: baseline saturation, growth charting (these children burn calories breathing), spirometry where possible. Fourth, build the care plan: home oxygen for frequent desaturation, calorie supplementation, full immunisation plus annual influenza, airway clearance physiotherapy taught to the mother, and a low antibiotic threshold for intercurrent infections. Fifth, therapeutic trials: monitored inhaled bronchodilator and corticosteroid (for any reversible component), and many units add thrice-weekly azithromycin for its anti-inflammatory effect, accepting the evidence is thin. Finally, set expectations — improvement over years, not weeks — with transplant counselling reserved for the progressive minority.
Where students slip
Bronchiolitis obliterans is confused with acute bronchiolitis by name; the exam stem always hides the 60-day persistence clause, so a toddler with unresolving crackles months after adenoviral pneumonia is post-infectious obliterans. Second, expecting a bronchodilator response — the obstruction is fibrotic and fixed, distinguishing it from asthma. Third, the mosaic pattern is attributed wrongly to pulmonary embolism (the adult connotation); in a post-infectious child it means air trapping from obliterated small airways.
Frequently asked questions
Which infection most often precedes post-infectious bronchiolitis obliterans in Indian children?
Adenovirus pneumonia (serotypes 3, 7 and 21), with measles, influenza, mycoplasma and pertussis also implicated.
What defines the diagnosis clinically?
Persistent tachypnoea, crackles, hypoxaemia and hyperinflation continuing beyond 60 days after a severe lower respiratory infection, in a child with poor bronchodilator response.
What is the characteristic HRCT finding?
Mosaic attenuation with air trapping on expiratory images, accompanied by bronchial wall thickening and bronchiectasis; a unilateral lucent lung with a small pulmonary artery defines Swyer-James-McLeod syndrome.
Is there any curative medical therapy?
None proven — corticosteroids and azithromycin are empirical; care rests on oxygen, nutrition, vaccination, physiotherapy and exacerbation treatment, with lung transplantation for end-stage disease.
How is bronchiolitis obliterans distinguished from asthma?
Fixed airflow obstruction without significant bronchodilator reversibility, persistent crackles and hypoxaemia, no atopic history, and mosaic air trapping on imaging rather than reversible hyperinflation.