Introduction Definition inflammation and fibrosis of the small airways (bronchioles) manifestation of chronic rejection in lung transplant (and allogenic bone marrow transplant) involves small bronchioles obstructive pattern on PFTs (reduced FEV1/ FVC) major problem in lung transplant patients vasculature is relatively unaffected unlike other examples of chronic organ rejection e.g. kidney Other etiologies viral infections collagen vascular diseases toxic fumes rheumatoid arthritis Pathophysiology lymphocytic inflammation of bronchiolar wall damage replaced by fibrous tissue progressive reduction in diameter of small airway lumens