Abstract
Recent studies elicited evolving concepts and controversies in interstitial lung diseases and proposed substantial changes in diagnostic and therapeutic approaches to interstitial lung diseases. Dr. Averill A. Liebow first coined the term usual interstitial pneumonia (UIP) in 1960’s as distinct pathologic pattern of fibrosis in idiopathic pulmonary fibrosis (IPF), the prototype of progressive fibrosing interstitial lung disease with poor prognosis. Advances in omics led to a better understanding of molecular pathogenesis of UIP and shed light on various types of familial pulmonary fibrosis as well as familial IPF. The concept of progressive pulmonary fibrosis was introduced to acknowledge additional types of progressive fibrosing interstitial lung diseases with the clinical and pathologic phenotypes very similar to those of UIP/IPF. As such, some authors have proposed a paradigm shift by considering UIP as a stand-alone diagnostic entity to encompass other fibrosing interstitial lung diseases that undergo the same relentless progression as IPF. Cicatricial organizing pneumonia is a variant of organizing pneumonia that can be reminiscent of UIP on histopathology but usually follows a stable clinical course unlike UIP. There has been significant disconnection in fundamental understanding as well as diagnostic criteria of lymphocytic interstitial pneumonia among pathologists, pulmonologists and radiologists, which needs to be resolved. The concept and histopathologic criteria of granulomatous and lymphocytic interstitial lung disease are also elusive and require clarification as well. In this review, these topics will be covered based on current literature.