Pulmonary fibrosis: a disease of alveolar collapse and collagen deposition.

Introduction: Idiopathic pulmonary fibrosis (IPF) is a relentless form of fibrotic lung disease with a median survival of approximately 3 years after diagnosis and a mortality rate that surpasses that of many types of cancer. The pathophysiology of IPF is complex as there are likely different stages of disease occurring simultaneously in the lung. Areas covered: Some scientists consider IPF as primarily an epithelial driven disease in which dysfunctional surfactant-producing cells take an etiological precedent. Others focus on the augmented deposition of collagen within the interstitium as the primary inciting event causing fibrosis. An increase in collagen deposition augmenting the tensile strength of the pulmonary interstitium fits with the well-known restrictive nature of fibrotic lung diseases; however, it fails to explain the creation of cystic 'honeycombing' lesions and the preference of such lesions for the peripheral and basilar lung parenchyma. Expert opinion: In this paper, we will review both ideas and propose incorporating them into a single pathophysiological chain-of-events that could account for all the features that characterize IPF, allowing us to envision new therapeutic approaches to improve patient outcomes.