Increased Micronodule Counts Are More Common in Occupationally Silica Dust–Exposed Smokers Than in Control Smokers

To determine the prevalence of increased micronodule counts in silica dust–exposed smokers. We evaluated 54 male smokers with severe silica dust exposure and 54 male control smokers. Both groups underwent low-dose chest computed tomography and lung function testing. Computed tomographic scans were visually evaluated for solid micronodules (<3 mm). The 95th percentile of micronodule count was calculated for the control smokers. Prevalence of an increased micronodule count was assessed for the dust-exposed subjects. Solid micronodules were present in most participants of both groups. The 95th percentile of micronodule count in the control group was 13. Increased micronodule counts were significantly more common in the exposed group than in the control group (P = 0.01). A substantial number of silica-exposed heavy smokers evaluated for silicosis have increased micronodule counts on chest computed tomographic scan. This finding might represent an early stage of silicosis.