Small airways (terminal or membranous bronchioles, respiratory bronchioles, and alveolar ducts) may be affected by exposure to both fibrous and nonfibrous mineral particles, including silica, silicates, coal dust, asbestos, iron, and mixed dusts. Small airways are often involved by macules and nodules of various dust exposures (see Chapter 85).

The term mineral dust-associated small-airway disease has been coined to describe fibrosis of small airways that evolves from nonfibrotic dust macules. There is deposition of mineral dusts and minimal fibrosis in the walls of the membranous bronchioles, respiratory bronchioles, and alveolar ducts. With time, the lesions may progress, with fibrotic distortion of the airways and focal emphysema of the adjacent parenchyma.

Dust-related small airway fibrosis involves the same anatomic locations as tobacco smoke: terminal (membranous) bronchioles and respiratory bronchioles. In the past, it was suggested that mineral dusts caused more respiratory bronchiolitis and that tobacco smoke caused more membranous bronchiolitis, but in recent years, respiratory bronchiolitis and respiratory bronchiolitis-associated interstitial lung disease have emerged as important tobacco-related lesions (see Chapters 64, 78, 79, and 80).