A 63-year-old man has had progressively worsening dyspnea over the past 10 years. He has noticed a 5-kg weight loss in the past 2 years. He has a chronic cough with minimal sputum production and no chest pain. On physical examination, he is afebrile and normotensive. A chest radiograph shows extensive interstitial disease. Pulmonary function tests show diminished DLCO, low FVC, and normal FEV1/FVC ratio. Increased exposure to which of the following pollutants is most likely to produce these findings?
Correct Answer: Silica
Description: Silica crystals incite a fibrogenic response after inhalation and ingestion by pulmonary macrophages. The greater the exposure to silica dust and the longer the time of exposure, the greater is the lung injury. Silica is a major component of the earth's crust, including sand, which contains the mineral quartz. Mining, manufacturing, farming, and construction/renovation activities generate small silica crystals that can be inhaled, and their buoyancy allows them to be carried to alveoli. There, they are ingested by macrophages, which secrete cytokines that recruit other inflammatory cells and promote fibrogenesis. Carbon monoxide readily crosses the alveolar walls and binds avidly to hemoglobin, but does not injure the lung directly. Ozone, a component of smog, has no obvious pathologic effects. Tobacco smoke leads mainly to loss of lung tissue and emphysema, not to fibrosis. Particulate matter such as wood dust is mainly screened out by the mucociliary apparatus of the upper airways, but may invoke bronchoconstriction.
Category:
Pathology
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