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The Overlap Between Respiratory Bronchiolitis and Desquamative Interstitial Pneumonia

The Overlap Between Respiratory Bronchiolitis and Desquamative Interstitial PneumoniaPulmonary Langerhans cell histiocytosis (PLCH) is an uncommon interstitial lung disorder that occurs almost exclusively in smokers. Cigarette smoking has also been implicated in the development of respiratory bronchiolitis (RB)-associated interstitial lung disease (ILD) [RB-ILD] and desquamative interstitial pneumonia (DIP), two uncommon ILDs with significant clinical and histopathologic overlap. These three ILDs are now often referred to as smoking-related ILDs, a term suggesting that PLCH, DIP, and RB-ILD may form a spectrum of patterns of interstitial lung injury that may occur in certain individuals who smoke. RB is a histologic lesion reported to occur in virtually all smokers. Since DIP is also etiologically linked to smoking, it is not unexpected that RB/DIP-like reactions frequently coexist in histologic specimens of PLCH, as reported in prior studies. review
However, very few studies describe the extent and clinical significance of RB/DIP-like changes on the lung biopsy and high-resolution CT (HRCT) of patients with PLCH. This descriptive retrospective study was prompted by the observation that in two individuals with histopathologically proven PLCH, chest HRCT demonstrated prominent ground-glass attenuation, accompanied with a marked RB/DIP-like reaction on the sampled lung tissue. This study was designed to identify the frequency and extent of RB/DIP-like changes in lung biopsy specimens of patients with PLCH, and correlate these findings with the HRCT and physiologic measures of lung function. We observed that RB/DIP-like changes were present in all PLCH biopsy specimens, and correlated with cumulative pack-years of cigarettes smoked, but did not correlate with measures of lung function. Of considerable interest is that in two patients, the extent of RB/DIP-like changes was very extensive, and was accompanied by ground-glass attenuation on HRCT.