Exploring the role of silica exposure in the aetiology of interstitial lung disorders

The paper by Iversen and colleagues 1 in this issue of Occupational and Environmental Medicine provides interesting insights into the potential contribution of inhaled respirable crystalline silica (RCS) in the development of idiopathic interstitial lung disorders and sarcoidosis.It also interestingly showed an association between low levels of cumulative RCS exposure and the presence of diagnosed silicosis.Importantly, it also reminds us about the uncertainties underlying current diagnostic practices, disease classification and knowledge about the lung's response to inhaled agents.What is certain is that occupational contributions to lung disease are frequently underestimated, and that better information is needed.The Iversen et al study followed more than 5.5 million workers (ie, practically the entire Danish working population) for more than 30 years, tracking their clinical presentation to the Danish healthcare system.Occupational exposure to RCS was estimated using a previously validated job exposure matrix 2 3 (JEM), and cases of idiopathic interstitial pneumonias (IIPs), pulmonary sarcoidosis and silicosis were identified from the Danish National Patient Register (DNPR).The IIPs likely included idiopathic pulmonary fibrosis (IPF), non-specific interstitial pneumonia (NSIP), the newly emerging genetic disorders and unclassifiable cases.For all studied lung disease outcomes except IPF, elevated incidence rate ratios (IRRs) were found associated with all RCS exposure categories.This is the first time, to our knowledge, that the IIPs were prospectively studied using a validated JEM to estimate RCS exposure; the JEM was based on a large number of RCS samples collected across many geographies and time periods.Although significantly increased risks from RCS exposure were observed for IIP and sarcoidosis, none were observed when IPF alone was assessed.This lack of a significant association with IPF is