The diagnostic accuracy of lymph node silicosis for pulmonary silicosis in South African gold miners.

Background: Lymph node silicosis (LNS) may be found when investigating lung and mediastinal diseases. Co-occurrence of LNS and pulmonary silicosis (PS) has been described but no studies have investigated the diagnostic accuracy of LNS for PS, the aim of this study.

Methods: This cross-sectional study included South African miners with exclusive gold-mining employment who had autopsy examinations from 1975 to 2018. Routinely recorded pathologist-diagnosed LNS and PS and occupational histories were retrieved from the PATHAUT database. Pulmonary silicosis was the reference standard. Sensitivity, specificity, positive and negative predictive values (PPV and NPV) and summary diagnostic accuracy were calculated overall and by PS severity and employment duration.

Results: Of the 69 802 miners, the prevalences of LNS and PS were 39.2% (n=27 373) and 17.7% (n=12 345), respectively. There were 24.1% false-positive LNS tests. Sensitivity was 85.2% (95% CI 84.6-85.6), but specificity was lower (70.7%, 95% CI 70.3-71.0). The PPV and NPV were 38.4% (95% CI 37.9-39.0) and 95.7% (95% CI 95.5-95.9), respectively. Sensitivity increased and specificity decreased with increasing employment duration.

Conclusions: Our findings are consistent with LNS occurring at concentrations of respirable crystalline silica too low to cause PS and possibly being a portent of PS. LNS had deficits as a diagnostic test for PS. The low PPV raises uncertainty about the presence of PS in patients with LNS. LNS may perform better in populations with higher prevalence of silicosis, for example in patients with clinically suspected PS.