Facts and controversies in the classification of idiopathic interstitial pneumonias

Idiopathic interstitial pneumonias are defined from the pathological point of view as non granulomatous intralobular inflammatory and fibrotic process es involving the alveolar walls. More than thirty years ago Liebow and Carr ington pioneered the notion that morphological characteristics could be use d with benefit in separating the different entities found in this group, wh ich present with typical, but not pathognomonic clinical features. In the m id-1980s some entities, including giant cell interstitial pneumonia (GIP) a nd lymphocytic interstitial pneumonia (LIP), were removed from this group a nd considered as peculiar forms. In the early 90s the concept of cellular o r nonspecific interstitial pneumonia was reconsidered, leading to an in dep th revision of various types of interstitial pneumonia of unknown etiology. The histological pattern observed in patients with idiopathic pulmonary fi brosis is now referred to as usual interstitial pneumonia (UIP). Other enti ties that have been revised during the last ten years are desquamative inte rstitial pneumonia/alveolar macrophage pneumonia (DIP/AMP), respiratory bro nchiolitis-interstitial lung disease (RB-ILD), acute interstitial pneumonia (AIP), cryptogenic organizing pneumonia (COP) and nonspecific interstitial pneumonia (NSIP). This paper provides a detailed description of pulmonary disorders which have been included in the new classification systems of idi opathic interstitial pneumonias. In the second part of the paper we will di scuss several doubts and controversies that this new classification schemes leave unresolved.