ABSTRACT
Diffuse interstitial lung disease (ILD) is a generic term encompassing a broad range of largely unrelated conditions that share the propensity to cause breathlessness and/or cough associated with bilateral abnormal opacities of various types on conventional chest radiographs or computed tomographic (CT) scans. The idiopathic interstitial pneumonias are a subset of diffuse interstitial lung diseases characterized by expansion of the interstitial compartment (i.e., that portion of the lung parenchyma sandwiched between the epithelial and endothelial basement membranes) by an infiltrate of inflammatory cells. The inflammatory infiltrate is sometimes accompanied by fibrosis either in the form of abnormal collagen deposition or proliferation of fibroblasts capable of collagen synthesis. Recent international consensus has defined these entities more specifically, with idiopathic pulmonary fibrosis (IPF) being based upon the histological appearances of a usual interstitial pneumonia (UIP) pattern, thus distinguishing it from other interstitial fibrosing pneumonias of known causes and those with different histological patterns of unknown cause (1).
