Granulomatous interstitial nephritis associated with silica

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A 25‐year‐old woman was referred to our hospital due to slightly elevated serum creatinine (114.9 μmol/L) without proteinuria and haematuria. She felt general fatigue, but physical examination was unremarkable. Urinary β2microglobulin excretion was high (117.0 nmol/L). We performed renal biopsy. The macroscopic appearance of the kidney specimen was dark brown. There were 12 glomeruli, eight of which showed global sclerosis. Interstitium shows mild lymphocytic infiltration and one epithelioid cell granuloma with focal tubulitis. Light microscopy showed brown granules in the epithelium of entire proximal tubules with focal dilatation (Fig. 1). Electron microscopy showed the number of lysosomes was increased in the epithelium of proximal tubules (Suppl. Fig. S1). Immunohistochemical stainings of myoglobin, HMB‐45, and iron for the granules were negative. So we performed metal analysis. The electron microscopy‐metal analysis indicated that the lysosomes include peaks of silica as well as other metals, which were used for staining (Suppl. Fig. S2 ①, ②, ③, and ④). The granules were found to be made of silica. We diagnosed granulomatous interstitial nephritis associated with silica, because there was no obvious background such as sarcoidosis or tuberculosis. Although the mechanism of silica nephropathy was not fully understood, granules formation was supposed to involve autoimmune disorder.1 After oral steroid therapy (max prednisolone 30 mg/day) for one year, we performed re‐biopsy. The macroscopic appearance of the kidney specimen was still dark brown. There were also brown granules in the epithelium of proximal tubules light microscopically. Inflammatory cells in the intestine were increased, but intestinal fibrosis was not progressed. The level of creatinine has been 114.9–132.6 μmol/L and urinary β2 microglobulin excretion was decreased (9.0 nmol/L). The reason for silica deposition in the kidney is still unknown.
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