Two Sides of the Same Smoke: Decoding Respiratory Bronchiolitis-Associated Interstitial Lung Disease (RB-ILD) and Alveolar Macrophage Pneumonia (AMP)

Respiratory bronchiolitis-associated interstitial lung disease (RB-ILD) and desquamative interstitial pneumonia (DIP) are two rare but closely related conditions within the spectrum of smoking-related interstitial pneumonias. Both are classified as idiopathic interstitial pneumonias and share characteristic histopathologic features, including the accumulation of pigmented alveolar macrophages alongside varying degrees of interstitial inflammation and fibrosis. RB-ILD is typically a localized, bronchiolocentric process often found in smokers, whereas DIP represents a more diffuse and clinically significant disease that may arise not only from tobacco smoke but also from other causes such as occupational exposures, autoimmune diseases, and drug reactions. This review highlights the clinical presentation, imaging findings, histopathology, and treatment of both entities, emphasizing their overlapping features as well as key distinctions. We further discuss the pathogenic mechanisms driven by cigarette smoke-including oxidative stress, immune activation, and fibrosis-that underlie these diseases. A clear understanding of the similarities and differences between RB-ILD and DIP is essential for accurate diagnosis, effective management, and prognostication, particularly in patients with a history of smoking and diffuse parenchymal lung involvement.