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The Overlap Between Respiratory Bronchiolitis and Desquamative Interstitial Pneumonia: PLCH biopsy specimens

Whereas RB is an extremely common lesion that refers to the universal inflammatory reaction found in the respiratory bronchioles of cigarette smokers, RB-ILD is an uncommon ILD that occurs in a small proportion of smokers. In analogy to DIP, the diagnosis of RB-ILD can only be made following careful exclusion of other histologic entities that may explain the presence of ILD.
What then is the clinical significance of determining RB/DIP-like changes on PLCH biopsy specimens? website
Although in the majority of patients with PLCH, the presence of associated RB/DIP-like changes is of little significance other than reflecting prior exposure to cigarette smoke, the current study suggests that occasionally, the extent of RB/DIP-like changes may be sufficiently severe to cause substantial interstitial thickening and partial alveolar filling to cause the appearance of ground-glass attenuation on the CT. Although uncommon, this observation has important diagnostic implications. As stated previously, in spite of the presence of RB- and DIP-like changes on lung biopsy specimens, one does not establish a diagnosis of DIP or RB-ILD in the presence of other distinct histopathologic lesions such as PLCH. Thus, traditionally, one would not consider these patients to have two diseases, ie, DIP or RB-ILD, and PLCH, but rather call this PLCH with prominent features of respiratory bronchiolitis or DIP-like changes. This is analogous to the demonstration that although a proportion of patients with usual interstitial pneumonia have areas of nonspecific interstitial pneumonia in different lobes, the lesion of usual interstitial pneumonia takes precedence as the principal diagnosis because it is this lesion that determines the outcome and prognosis. The relative role of RB/DIP-like changes and PLCH lesions to the physiologic and functional impairment seen in these patients is not clear.