Respiratory bronchiolitis-associated interstitial lung disease with fibrosis is a lesion distinct from fibrotic nonspecific interstitial pneumonia: a proposal.

Nine cases of clinical and radiographic chronic interstitial lung disease are presented that have features of respiratory bronchiolitis-associated interstitial lung disease, but were associated with a respiratory bronchiolitis having extensive paucicellular lamellar eosinophilic collagenous thickening of alveolar septa in a patchy, particularly subpleural distribution. Patients were middle-aged with shortness of breath, mixed obstructive and restrictive lung disease with markedly reduced diffusing capacity and radiographs demonstrating centrilobular micronodules, occasional ground glass opacities and emphysema. All were alive at follow-up. The morphology of this process raises the differential diagnosis with the fibrotic form of nonspecific interstitial pneumonia and highlights the role of cigarette smoking as a potential cause of fibrotic lung disease.