Progression of Idiopathic Pulmonary Fibrosis Is Associated with Silica/Silicate Inhalation

Recently, environmental dust exposure has emerged as a possible risk factor for interstitial pneumonia. Inhaled silica/silicates and titanium are associated with the progression of rapidly progressive pneumoconiosis. However, the relationship between inhaled elements and idiopathic pulmonary fibrosis (IPF) remains unclear. In this study, we focused on IPF presenting with histological usual interstitial pneumonia and investigated the relationship between inhaled elements and IPF progression. We examined the elements in the lungs using in-air micro-particle-induced X-ray emission analysis (PIXE). Lung tissue samples with IPF were analyzed and compared with control lung samples. There was a significant difference between IPF and the control lungs in terms of silicon, assumed to form silica/silicates. Inhaled silicon in the lungs significantly correlated with the annual decline in forced vital capacity in patients with IPF. Furthermore, IPF patients with higher accumulation of silicon showed a significantly poorer prognosis than those with lower accumulation of silicon in the lungs. These significant differences were also seen in multivariate analyses, including smoking history, IPF severity, and/or antifibrotic treatment. In-air micro-PIXE can be beneficial for detecting inhaled elements in the lung. These results indicate that inhaled silica/silicates in the lung may be partly involved in the progression of IPF.