Overview of Interstitial Lung Disease (Diffuse Parenchymal Lung Diseases) By Joyce Lee, MD, MAS, University of Colorado School of Medicine Reviewed / Revised Jun 2021 | Modified Sep 2022 View Patient Education Topic Resources Causes of Interstitial Lung... Interstitial lung diseases are a heterogeneous group of disorders characterized by alveolar septal thickening, fibroblast proliferation, collagen deposition, and, if the process remains unchecked, pulmonary fibrosis.