Comparative elemental analysis of collagen vascular-associated lung diseases by in-air micro- PIXE, a pilot study

Background: Collagen vascular disease (CVD) is a systemic disease in which connective tissue abnormalities of systemic organs such as the skin, kidneys, lungs, and lymph nodes are caused by abnormal functions of the immune system. The cause of CVD has not been clarified yet, but it has been suggested that exposure to heavy metals and silica may be the cause of vasculitis and systemic sclerosis. Purpose: In this study, we focused on the elemental analysis of lung tissues complicated with collagen vascular disease-associated interstitial lung disease (CVD-ILD) and investigated the relationship between inhaled elements and CVD-ILD. Methods: We examined the inhaled elements in the lungs using in-air micro-particle-induced X-ray emission analysis (in-air micro-PIXE). Elemental analysis of lung tissue specimens was performed by using 5 cases of systemic sclerosis and 3 cases of aminoacyl-tRNA synthetase (ARS) antibody-positive dermatomyositis surgically resected by thoracoscopic lung biopsy. Control lung samples were obtained from early-stage lung cancer patients. The relative amounts of each elements divided with sulfur in the lung was statistically analyzed. Results: There was a significant difference between CVD-ILD and the control lung in terms of inhaled silica/silicates. Furthermore, relative silica deposition was higher in scleroderma lungs compared to control lungs, but not in lungs from ARS-positive cases. Conclusion: These results indicated that silica deposition in lung tissue may be involved in the pathogenesis of CVD-ILD, especially systemic sclerosis.