Inhalation of inorganic particles as a risk factor for idiopathic pulmonary fibrosis--elemental microanalysis of pulmonary lymph nodes obtained at autopsy cases

Exposure to inorganic particles may induce fibrosis in the lung. However, the association between exposure to inorganic particles and the pathogenesis of idiopathic pulmonary fibrosis (IPF)/usual interstitial pneumonia (UIP) is obscure. We examined inorganic particles in the pulmonary hilar lymph nodes affected by IPF/UIP to investigate whether inhaled elements are involved in the etiology, and whether there is an increasing risk of developing IPF/UIP. Twenty-three IPF/UIP cases and 23 controls without IPF/UIP were investigated. Pulmonary hilar lymph nodes constituted the study material. The elemental analysis was performed using scanning electron microscopy with an energy dispersive X-ray spectroscope, and we analyzed particles quantitatively and qualitatively. The results showed that the cases contained silicon and aluminum as compared with the control in lymph nodes, and these deposits were statistically significantly associated with an increased risk of IPF/UIP (adjusted odds were 2.99, 95% CI: 1.29-6.85 and 57.84, 95% CI: 1.45-2306.19, respectively). In addition, higher nickel levels in lymph nodes were associated with lung cancer. This study shows that inorganic particles, such as Si and Al, have higher concentrations in the hilar lymph nodes in IPF/UIP, and may play a role in one of the risk factors in the pathogenesis of IPF/UIP.