The Overlap between Respiratory Bronchiolitis and Desquamative Interstitial Pneumonia in Pulmonary Langerhans Cell Histiocytosis: High-Resolution CT, Histologic, and Functional Correlations

Objectives: To characterize the histologic, high-resolution CT (HRCT), and functional correlates of respiratory bronchiolitis (RB)/desquamative interstitial pneumonia (DIP)-like changes in biopsy specimens of adults with pulmonary Langerhans cell histiocytosis (PLCH). Methods: We retrospectively identified 14 adult patients with histologically proven PLCH (all smokers) in whom both biopsy specimens and HRCT were available for review. The presence and extent of RB/DIP-like changes on lung biopsy specimens of patients with PLCH were correlated with total pack-years of smoking, lung function variables, and the presence of ground-glass attenuation on HRCT. Results: Varying degrees of RB/DIP-like changes were identified in all biopsy specimens. The extent of involvement with RB/DIP-like changes correlated with the cumulative exposure to cigarettes smoked at the time of biopsy (r = 0.61, p = 0.03). Ground-glass attenuation was detected in three HRCTs, two of which had extensive RB/DIP-like changes (≥ 70% involvement) on histology, suggesting that substantial smoking-induced RB/DIP-like changes may be the cause of ground-glass attenuation on the HRCT of patients with PLCH. No correlation was found between the extent of RB/DIP-like changes and total lung capacity, FEV₁, or diffusion capacity of the lung for carbon monoxide. Conclusions: RB/DIP-like changes are exceedingly common in PLCH, may be sufficiently severe to cause the appearance of ground-glass attenuation on HRCT, and correlate with the cumulative exposure to cigarettes smoked. This study provides additional evidence that PLCH, RB, and DIP form a spectrum of interstitial patterns of lung injury to cigarette smoke.