A child presents to the emergency depament with fever and mild respiratory distress. He was staed on oral antibiotics and showed initial improvement, but later deteriorated again with fever, wheeze and exaggerated breathlessness. Radiographs of chest showed hyperluscency and Pulmonary Function Tests showed an obstructive pattern. The most probable diagnosis is:

The patient in question is presenting with features of bronchiolitis obliterans. Bronchiolitis obliterans is a small airway disease that is histologically charecterised by proliferation of fibrous tissue in the bronchiolar walls. It produce irreversible airway obstruction. Clinical features: wax and wane in between. Most common symptoms are fever, cough with sputum, dyspnea with wheeze. Investigation: Xray shows hyperlucent lung, Pulmonary function testing shows obstructive pattern. Ref: Severe asthma: pathogenesis and clinical management By S. J. Szefler, Donald Y. M. Leung page 288; Imaging in Pediatric Pulmonology By Robe Cleveland page 237. 3. Pediatric Chest Imaging: Chest Imaging in Infants and Children By Javier Lucaya page 108; Imaging of the newborn, infant, and young child By Leonard E. Swischuk page 122.