C61-19 Progressive Tracheobronchial Dilation in Post-Infectious Bronchiolitis Obliterans: Overlap With Mounier-Kuhn Syndrome

Introduction Post-infectious bronchiolitis obliterans (PIBO) is a severe obstructive lung disease that develops after lower respiratory tract infections. Large airway involvement is rarely described. Mounier-Kuhn syndrome (MKS) is a distinct disorder characterized by marked dilation and diverticula of the trachea and main bronchi, often associated with recurrent infections and impaired mucociliary clearance. To our knowledge, the coexistence of PIBO and MKS has not been reported previously. We present a patient who was initially diagnosed with PIBO who later developed type 3 MKS. Case Description A 16-year-old male developed PIBO after adenovirus infection in infancy, confirmed by high-resolution chest CT at age 8 months. Imaging also indicated tracheal dilation (figure1). Despite treatment with corticosteroids and methotrexate, his respiratory failure progressed to tracheostomy and ventilator dependence by 1 year of age. His course was complicated by recurrent spontaneous pneumothorax requiring bilateral pleurodesis. Between ages 7 and 14 years, he demonstrated clinical stability with adequate gas exchange and growth, sprinting to 2 L/Min oxygen flow during the day, yet at age 15 years he developed new hypoventilation and chest CT revealed subpleural bullae, tracheobronchial enlargement, and worsened tracheal dilation and bronchiectasis with disproportionate bronchial dilation, severe hyperinflation, presence of several deep tracheobronchial diverticula(figure 1). Decreasing ventilator pressures and increasing inspiratory time improved hyperinflation and hypoventilation. Flexible bronchoscopy confirmed multiple posterior tracheal diverticula extending into the right main bronchus and distal right-sided airways, mucosal striations, and severe tracheobronchomalacia (figure 1). He was initiated on IVIG for immune modulation, with aggressive airway clearance with the plan for pulmonary rehabilitation going forward. Discussion This case illustrates an unusual presentation of tracheal enlargement and airway diverticulosis in a patient with long-standing PIBO. Several studies have noted associated central airway dilatation proportional to disease severity. Prolonged positive-pressure ventilation, high peak inspiratory pressures, and impaired secretion clearance can further stretch and thin airway walls, predisposing to acquired diverticula. MKS is a rare congenital tracheobronchomegaly characterized by loss of elastic tissue and multiple diverticula. We have not uncovered other reports describing the coexistence of PIBO and MKS Whether the diverticula represent sequelae of chronic inflammation or iatrogenic injury is uncertain, but aggressive airway clearance, immune modulation, and optimization of ventilator pressures may mitigate further airway remodeling. Recognition of large-airway complications in chronic PIBO broadens our understanding of post-infectious airway pathology and underscores the need for individualized ventilatory and clearance strategies.