ABSTRACT
The term "interstitial lung diseases" (ILDs) includes a set of diseases characterized by a diffuse infiltration of the interstitium. There are more than 200 causes of ILDs that are classified into four main categories: (a) interstitial pneumonitis of known cause, including those associated with a connective tissue disease, secondary to drug-related injury or from environmental exposure; (b) idiopathic ILDs; (c) granulomatous diseases—sarcoidosis; and (d) rare ILDs, including lymphangioleiomyomatosis (LAM), Langerhans cell histiocytosis (LCH), eosinophilic lung diseases, and pulmonary alveolar lipoproteinosis (PALP). The pulmonary interstitium is a collection of loose connective tissue surrounding the bronchovascular structures and extending into the inter/intralobular septas and the subpleural space. On pulmonary function tests, there is classically a reduction in vital capacity, lung volumes, and diffusing capacity of the lung for carbon monoxide (DLCO). Radiotherapy used for the treatment of some neoplasms, such as cancer of the lung, breast, esophagus, and for lymphoma, can cause an ILD.
