Type II cell hyperplasia is minimal. Try to trace the alveolar walls to verify the intact architecture. Stains for iron are negative or faintly positive, indicating that the brown pigment is not hemosiderin. It probably represents an accumulation of lysosomes with undigested debris. Both occur mainly in cigarette smokers.
Most heavy smokers have some chronic bronchiolitis and respiratory bronchiolitis.
In a few, however, the changes can be quite pronounced, and the patient complains of dyspnea, cough, and sputum production. The chest radiograph may show a reticular pattern. Histologically, the changes are similar to those described above for DIP, but they are confined to the peribronchiolar region, rather than being diffuse. Katzenstein A-L, Myers J. Idiopathic pulmonary fibrosis. Clinical relevance of pathologic classification.