Histologically, it is very similar to sarcoidosis. The pulmonary granulomas become progressively fibrotic and may lead to cor pulmonale and respiratory failure. The pathologic changes of patients who have adult respiratory distress syndrome are termed diffuse alveolar damage. In the initial or acute stage the alveolar walls are lined by hyaline membranes consisting of fibrin, edema, and fragments of necrotic epithelial cells. After two to three days, there is progressive interstitial and intra-alveolar fibroblast proliferation.
Hyaline membranes become less prominent.
This stage is termed the organizing stage . The histologic hallmarks of chronic bronchitis are subtle. There is an increase in the mucus glands lining the trachea and bronchi. There is an increase in the number of goblet cells lining bronchi and bronchioles. Sometimes there is a chronic inflammatory infiltrate in the submucosa and submucosal glands.