Interstitial lung disease, also known as diffuse parenchymal lung disease, is a group of lung diseases affecting the interstitium. It concerns alveolar epithelium, pulmonary capillary endothelium, basement membrane, perivascular and perilymphatic tissues.
The term ILD is used to distinguish these diseases from obstructive airways diseases. Interstitial lung disease may be broadly categorized into known and unknown causes. Common known causes include autoimmune or rheumatologic diseases, occupational and organic exposures, medications, and radiation. Interstitial lung disease of unknown cause is predominated by idiopathic pulmonary fibrosis, a specific and progressive fibrotic lung disease, followed by the idiopathic interstitial pneumonias, such as nonspecific interstitial pneumonia and sarcoidosis.