Clinical Scenario
A previously healthy 6-year-old boy is evaluated for persistent cough, exertional dyspnea, and wheezing for 4 months following hospitalization for severe adenoviral pneumonia requiring mechanical ventilation. Despite appropriate inhaled corticosteroid and bronchodilator therapy, his symptoms have shown minimal improvement. Examination reveals tachypnea, bilateral fine crackles, and prolonged expiration. Spirometry demonstrates an obstructive ventilatory defect with minimal bronchodilator reversibility.
High-resolution computed tomography (HRCT) of the chest demonstrates patchy areas of decreased lung attenuation with corresponding reduction in pulmonary vessel calibre. Expiratory images reveal persistent lobular areas of low attenuation consistent with air trapping, accompanied by mild cylindrical bronchiectasis.
Which of the following is the most likely diagnosis?
A. Asthma with persistent airflow limitation
B. Bronchiolitis obliterans
C. Cystic fibrosis
D. Primary ciliary dyskinesia
E. Protracted bacterial bronchitis
Correct Answer and Explanation
Correct answer: B.
Explanation: bronchiolitis obliterans
Post-infectious bronchiolitis obliterans (PIBO) is a chronic obstructive small-airway disease that develops after severe lower respiratory tract infection. Adenovirus, particularly types 3, 7, and 21, is an important infectious trigger in children.
The diagnosis is supported by the combination of:
Characteristic clinical history: Persistent cough, wheezing, and exertional dyspnea following severe adenoviral pneumonia.
Fixed airflow obstruction: Spirometry demonstrates obstruction with little or no reversibility after bronchodilator administration.
Characteristic HRCT findings: Mosaic attenuation, expiratory air trapping, and associated bronchiectasis.
The underlying pathological process involves injury to the bronchiolar epithelium followed by inflammation and fibrotic narrowing or obliteration of the small-airway lumen.
HRCT findings: High-yield examination points
Important distinction: Mosaic attenuation is not specific to bronchiolitis obliterans; it may also occur in asthma, vascular disorders, and other small-airway diseases. The clinical history and expiratory HRCT findings are essential to interpretation.
Why are the other options incorrect?
A. Asthma with persistent airflow limitation: Asthma typically has variable symptoms and may demonstrate bronchodilator responsiveness. Persistent fixed obstruction can occur in severe asthma, but the history of severe adenoviral pneumonia followed by continuous symptoms and characteristic HRCT abnormalities strongly favours PIBO.
C. Cystic fibrosis: Cystic fibrosis can cause bronchiectasis and chronic obstructive lung disease. However, the vignette lacks supporting features such as recurrent sinopulmonary infections, chronic productive cough, pancreatic insufficiency, or other evidence of cystic fibrosis.
D. Primary ciliary dyskinesia: This disorder commonly presents with chronic wet cough, persistent rhinosinusitis, recurrent otitis media, and sometimes situs abnormalities. The characteristic history of persistent obstruction immediately following severe viral pneumonia is more suggestive of PIBO.
E. Protracted bacterial bronchitis: This condition typically causes a chronic wet cough that improves with an appropriate course of antibiotics. It does not usually produce the combination of fixed airflow obstruction and extensive expiratory air trapping described here.
Clinical Pearl
In a previously healthy child with persistent wheezing and fixed airflow obstruction after severe lower respiratory tract infection, particularly adenoviral pneumonia, mosaic attenuation with expiratory air trapping on HRCT should raise strong suspicion for post-infectious bronchiolitis obliterans.
HRCT is the principal non-invasive imaging investigation. Lung biopsy may establish histopathological confirmation in selected cases, but it is not required in every child with a characteristic clinical and radiological presentation.
Practice more postgraduate-level pediatric respiratory MCQs for MRCPCH, FCPS, MD Pediatrics, and Board Examination preparation on PediatricExamGuide.com.
HRCT Findings in Bronchiolitis Obliterance
| HRCT finding | Interpretation |
|---|---|
| 01FindingMosaic attenuation | InterpretationPatchwork of relatively hypoattenuated and normally or more densely attenuated lung regions |
| 02FindingExpiratory air trapping | InterpretationAffected lung regions fail to increase in attenuation and decrease in volume normally during expiration |
| 03FindingReduced calibre of vessels in hypoattenuated regions | InterpretationReflects reduced regional perfusion associated with small-airway obstruction |
| 04FindingBronchial wall thickening | InterpretationAssociated airway inflammation and remodelling |
| 05FindingBronchiectasis | InterpretationMay develop as a consequence of chronic airway injury |
References
Postinfectious Bronchiolitis Obliterans in Children: Diagnostic Workup and Therapeutic Options — Workshop Report. Annals of the American Thoracic Society. 2020.
Postinfectious Bronchiolitis Obliterans in Children. Review of clinical features, HRCT findings, and diagnostic criteria.
Nelson Textbook of Pediatrics, 22nd edition — Bronchiolitis Obliterans. Chapter 443.1.
