A 43-year-old man with a long history of dyspnea which had progressively worsened over the preceding month is presented.

He had worked in an antimony mine for 3 years. Radiologically, there were diffuse reticulonodular shadowing opacities in both lung parenchymas. Histopathologic examination of the open-lung biopsy specimen revealed alveolar spaces filled with dust-laden macrophages and amorphous proteinaceous semifluid, the latter being immunoreactive for Human Surfactant Apoprotein A, associated with marked interstitial accumulation of the similar-looking macrophages along the bronchovascular bundles and mild interstitial fibrosis. Silicotic nodules or mixed dust fibrosis were not seen. The patient was diagnosed as silicoproteinosis with unusual histopathological features because he had worked in an antimony mine for only 3 years and had 86% silica in a mineralogical analysis.

Pneumoconiosis is a rare lung disease which may be confused with other interstitial lung diseases. Clinical, radiological and unusual histopathologic features of this rare case are presented and discussed with the differential diagnosis, especially of mixed dust pneumoconiosis.