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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.