Persistent radiological changes following miliary tuberculosis in miners exposed to silica dust.

SETTING: Silicosis leads to increased susceptibility to tuberculosis, but it has also been suggested that tuberculosis may interact with intra-pulmonary silica to exacerbate fibrotic lung disease. OBJECTIVES: To investigate the possibility that silicosis developed due to or was exacerbated by tuberculosis. METHODS: In a case series of 15 miners presenting with culture-positive miliary tuberculosis, serial radiographs taken premorbidly, at presentation, and after 2 and 6 months of standard anti-tuberculosis treatment were graded for nodularity using the International Labour Organization system. RESULTS: Increased nodule profusion (compared to premorbid film) remained in 13 (87%) and eight (53%) patients after 2 and 6 months of treatment, respectively, despite clinical improvement in all and documented bacteriological cure in eight (53%). These phenomena, observed irrespective of human immunodeficiency virus (HIV) status, were most pronounced in men with minor premorbid changes. Abnormal pulmonary collagenisation related to silica particles was apparent at post-mortem in two men who died of HIV-associated cryptococcosis after completing TB treatment. CONCLUSIONS: Previous silica exposure appears to result in delayed and potentially incomplete radiological resolution of miliary TB. We postulate that the immune response in tubercles may evoke a 'bystander' fibrotic response, as cytokines play a central role in the pathogenesis of both TB and silicosis.