A 3 month old child has moderate fever and non productive cough and mild dyspnea. After course of mild antibiotic the condition of the child improved transiently but he again developed high fever, productive cough and increased respiratory distress. Chest X ray shows hyperlucency and PFT shows obstructive pattern. 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 commonly with adenovirus. Children with bronchiolitis obliterans usually experience dyspnea, coughing, and exercise intolerance. Chest radiograph abnormalities include evidence of heterogeneous air trapping and airway wall thickening. 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.