Desquamative interstitial pneumonia and respiratory bronchiolitis-associated interstitial lung disease

Our understanding of the various types and patterns of diffuse lung disease that might result in fibrosis has evolved considerably over the last 50 years. Many entities now regarded as distinct had been previously "lumped" together as a single disease, "lung fibrosis," and more recently misdiagnosed as idiopathic pulmonary fibrosis (IPF, synonymous with cryptogenic fibrosing alveolitis). In 1965 desquamative interstitial pneumonia (DIP) was first described, and later it was clearly demonstrated that the clinical and pathological features of DIP and IPF were different, particularly in terms of survival and response to therapy. They are not part of the same disease spectrum nor does DIP evolve into usual interstitial pneumonia (UIP). Later, in the mid-1980s, RBILD was described as a distinct clinicopathologic syndrome with features consistent with an interstitial lung disease among current or former smokers. In the recent histopathological classification of idiopathic interstitial pneumonia (IIP), DIP and RBILD have been included as separate entities, although there is some evidence that suggests they may lie at the two ends of a single spectrum. The debate bears similarities with the debate about DIP and UIP and is as yet unresolved. This article will give a broad and current overview of these two rarer forms of IIP, including issues that relate to diagnosis, imaging, histopathology, treatment, and prognosis.