Challenges in pulmonary fibrosis x 5: the NSIP/UIP debate.

Among the idiopathic interstitial pneumonias, the two entities-idiopathic pulmonary fibrosis (IPF) characterised by the presence of the usual interstitial pneumonia pattern of histopathology (IPF/UIP) and non-specific interstitial pneumonia (NSIP; same nomenclature for the histopathological pattern and idiopathic disease) - have provoked considerable debate. IPF/UIP and NSIP closely mimic each other clinically but NSIP has a far better outcome. However, it remains unclear if NSIP is a truly separate and distinct entity. The histopathological pattern of NSIP can be found in a wide variety of clinical and radiological contexts. This review addresses these and other uncertainties regarding NSIP and UIP.