Interstitial Lung Disease (ILD)

In an apparent immunocompetent host, interstitial lung disease (ILD) is a clinical term for a heterogenous group of lower respiratory tract disorders with many potential causes. Common initial features include exertional dyspnea, a restrictive pattern of physiologic abnormality on pulmonary function testing , decreased diffusing capacity (DLCO), increased alveolar-arterial oxygen difference (Pao2 — Pao2) at rest or during exertion, and absence of pulmonary infection or neoplasm.

ILDs comprise several acute and chronic lung disorders with variable degrees of pulmonary fibrosis.The term interstitial in the commonly used acronym ILD is a misnomer because the pathophysiologic processes are not restricted to the interstitium, which is the microscopic space bounded by the basement membranes of epithelial and endothelial cells.

Rather, all of the several cellular and soluble constituents that make up the gas exchange units (alveolar wall, capillaries, alveolar space, and acini), bronchiolar lumen, terminal bronchioles, and pulmonary parenchyma beyond the gas exchange units (as well as the pleura, lymphatics, and sometimes the lymph nodes) are involved in the pathogenesis and manifestations of ILD.