[Small airway changes in acute interstitial pneumonia and acute exacerbation of chronic interstitial pneumonia]

To study pathologic changes in small airways in acute interstitial pneumonia (AI), changes in the terminal or respiratory bronchioles in one patient with AI and in three patients with acute exacerbations of chronic interstitial pneumonia (grouped together as the AI group) were compared to those in five patients with chronic idiopathic interstitial pneumonia (IIP) without acute exacerbation. Specimens obtained during autopsy were examined by light microscopy. In the AI group, mononuclear cells had infiltrated the lumen in 47 (23.7%) of the 198 bronchioles examined, and granulation tissue was found in 101 (51.0%). In the IIP group, no changes were found in 37 (97.4%) of the 38 bronchioles examined. Therefore, mononuclear cell infiltration and granulation tissue are common in the bronchioles of patients with acute interstitial pneumonia, but not in those of patients with chronic interstitial pneumonia without acute exacerbation.