A 3-month-old child has moderate fever and non productive cough and mild dyspnea. After a course of antibiotic, the condition of the child improved transiently but he again develops high fever, productive cough and increased respiratory distress. CXR shows hyperlucency and PFT shows obstructive pattern. Most probable diagnosis is:

d. Bronchiolitis obliterans(Ref: Nelson's 20/e p 2044-2047, Ghai 8/e p 381-382)Bronchiolitis obliterans (BO)What is it?A chronic obstructive lung disease of bronchioles and smaller airways, that results from an insult to the lower respiratory tract leading to fibrosis of small airwaysPathogenesis* After the initial insult, inflammation affecting terminal bronchioles, respiratory bronchioles and alveolar ducts can result in the obliteration of the airway lumen* Epithelial damage resulting in abnormal repair is characteristic of BO* Complete or partial obstruction of the airway lumen can result in air trapping or atelectasisClinical features* Cough, fever, cyanosis, dyspnea, chest pain and respiratory distress followed by initial improvement* It is easily confused with pneumonia, bronchitis, or bronchiolitis* Progression of disease with increasing dyspnea, chronic cough, sputum production and wheezing seenDiagnosis* Chest X-ray may be normal or can demonstrate hyperlucency and patchy infiltrates* Occasionally, a Swyer-James syndrome (unilateral hyperlucent lung) develops* PFT shows obstructive pattern