Lung

• Common histologic marker of current or former smoker status
• Usually an incidental pathologic finding but can occasionally be associated with clinically significant interstitial lung disease (respiratory bronchiolitis interstitial lung disease [RB-ILD])

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Contributed by Kristine Konopka, M.D.

• Desquamative interstitial pneumonia (DIP):
  • Substantial histologic overlap with respiratory bronchiolitis interstitial lung disease
  • Diffuse accumulation of pigmented macrophages beyond the peribronchiolar airspaces into the distal airspaces
  • Degree of interstitial fibrosis and inflammation usually greater than in respiratory bronchiolitis interstitial lung disease
• Hemosiderosis:
  • Potential etiologies: diffuse alveolar hemorrhage or chronic passive vascular congestion
  • Hemosiderin pigment darker and coarser than smoker's pigment
  • Iron stain can help in highlighting iron encrustation of vascular elastica (endogenous pneumoconiosis), a finding seen in chronic hemorrhage or chronic passive congestion

The findings in this lung wedge biopsy are associated with

1. Aspiration
2. Cigarette smoking
3. Exposure to inhaled bird antigens
4. Median survival of 2.5 years from diagnosis
5. Type I hypersensitivity reaction

B. Cigarette smoking. The image shows respiratory bronchiolitis, characterized by the accumulation of pigmented (smoker's) macrophages within distal airspaces. Aspiration usually results in amorphous or birefringent particulates within distal airspaces. Answer C is associated with hypersensitivity pneumonia, while type I hypersensitivity reactions are associated with atopic asthma. Respiratory bronchiolitis is a marker of current or former smoker status and is usually of no clinical consequence with no deaths attributable to it.

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Reference: Respiratory bronchiolitis

A 64 year old man with extensive smoking history undergoes lung wedge biopsy for evaluation of progressive exertional dyspnea and a restrictive defect on pulmonary function tests. Sections of the wedge biopsy show accumulation of lightly pigmented macrophages within distal airspaces. This is accompanied by patchy interstitial fibrosis that is associated with areas of architectural distortion and lung remodeling in the forms of scarring and honeycomb change. Based on these findings, which of the following is the best diagnosis?

1. Desquamative interstitial pneumonia (DIP)
2. Diffuse alveolar hemorrhage
3. Respiratory bronchiolitis interstitial lung disease (RB-ILD)
4. Smoking related interstitial fibrosis (SRIF)
5. Usual interstitial pneumonia (UIP)

E. Usual interstitial pneumonia (UIP). Although the features of respiratory bronchiolitis are present in the wedge biopsy sections and the patient has clinically significant interstitial lung disease, the diagnosis of respiratory bronchiolitis interstitial lung disease requires that other forms of diffuse lung disease have been ruled out. In this case, the findings of patchy interstitial fibrosis and honeycombing are consistent with usual interstitial pneumonia, which is the best explanation for this patient's symptoms and pulmonary function testing results.

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Reference: Respiratory bronchiolitis