Chronic interstitial pneumonia in silicosis and mix-dust pneumoconiosis: its prevalence and comparison of CT findings with idiopathic pulmonary fibrosis.

BACKGROUND: Increased prevalence of chronic interstitial pneumonia (CIP) is reported in dust-exposed subjects. We investigated the prevalence of CIP in silicosis and mixed-dust pneumoconiosis and sought morphologic differences of CIP between the pneumoconiosis and idiopathic pulmonary fibrosis (IPF).
METHODS: We reviewed CT scans of 243 silicosis and mixed-dust pneumoconiosis patients to identify any cases of parenchymal lung lesions showing a CIP pattern, and compared the CT findings with those of 62 patients with IPF. Two observers independently scored CT images and classified the CT pattern as typical or not typical for IPF. Differences were sought between the groups using a nonparametric test, Fisher exact test, and a logistic regression analysis. A radiopathologic correlation was performed in 11 pneumoconiosis patients.
RESULTS: Twenty-eight patients (11.5%) showed CIP on CT. Seven patients (25%) showed a pattern not typical of IPF, while the remaining patients showed a pattern typical of IPF, 11 of which were confirmed pathologically. The extent of fibrosis did not differ between the groups; however, patients with pneumoconiosis showed less traction bronchiectasis (odds ratio [OR], 0.19; 95% confidence interval [CI], 0.08 to 0.48; p < 0.001), more subpleural homogeneous attenuation (OR, 2.56; 95% CI, 1.55 to 4.23; p < 0.001), and fibrosis was more randomly distributed (OR, 315.38; 95% CI, 4.68 to 21244.63; p = 0.007). Pathologically, subpleural homogeneous attenuation corresponded to dense fibrosis often with abundant silicotic nodules.
CONCLUSIONS: Prevalence of CIP in pneumoconiosis was approximately 12% on CT. One fourth of patients showed an atypical IPF pattern, and the others showed a typical IPF pattern.