A 9 year old girl is presenting with non productive cough and mild stridor for 2.5 months duration. Patient is improving but suddenly developed wheeze, productive cough, mild fever and on X-ray hyperlucency is seen and PFT shows obstructive curve. The MOST probable diagnosis is?

Bronchiolitis obliterans is a rare chronic obstructive lung disease characterized by complete obliteration of the small airways following a severe insult. The most common form in children is postinfectious, following a lower airway tract infection with adenovirus, although influenza, rubeola, Bordetella, and Mycoplasma are also implicated. Persons with bronchiolitis obliterans usually experience dyspnea, coughing, and exercise intolerance. This diagnosis should be considered in children with persistent cough, wheezing, crackles, or hypoxemia persisting longer than 60 days following a lower respiratory tract infection. Chest X-ray shows hyperlucency and patchy infiltrates. PFT shows airway obstruction. Ventilation-perfusion scans show a pattern of ventilation and perfusion mismatch. Classic findings on chest high-resolution CT include a mosaic perfusion pattern, vascular attenuation, and central bronchiectasis. This finding along with pulmonary function testing showing airway obstruction unresponsive to bronchodilators may be diagnostic in some patients with the appropriate clinical history. Diagnosis is by open lung biopsy or transbronchial biopsy. No specific treatment is required. Administaion of coicosteroids may be benifical. Ref: Federico M.J., Stillwell P., Deterding R.R., Baker C.D., Balasubramaniam V., Zemanick E.T., Sagel S.D., Halbower A., Burg C.J., Kerby G.S. (2012). Chapter 19. Respiratory Tract & Mediastinum. In W.W. Hay, Jr., M.J. Levin, R.R. Deterding, J.J. Ross, J.M. Sondheimer (Eds), CURRENT Diagnosis & Treatment: Pediatrics, 21e.