SILICA NEPHROPATHY CAUSED BY LONG-TERM EXPOSURE TO DIATOMACEOUS EARTH IN A HOME BEDROOM: A 20-YEAR COURSE OF PROGRESSIVE KIDNEY DYSFUNCTION

Although silica nephropathy is rarely reported among farm, mine, and glass factory workers, there are no reports of it in non-workers exposed to diatomaceous earth at home. Here, we present a case of silica nephropathy that progressed to chronic kidney disease (CKD) stage 4 due to intermittent exposure to diatomaceous earth at home over approximately 20 years.

A 38-year-old woman with no family history of kidney disease and no history of abnormal findings on school urine tests. During a health checkup at age 20, mild renal impairment was noted with serum creatinine (sCr) 0.7 mg/dL and estimated glomerular filtration rate (eGFR) 70 mL/min/1.73m2. Kidney function progressively declined over time. At age 25, she presented with ground-glass opacities in both lower lung fields, sCr 1.3 mg/dL, eGFR 43 mL/min/1.73m², negative urine protein, and negative urine occult blood. A percutaneous renal biopsy performed by the previous physician revealed findings consistent with epithelioid cell granulomatous interstitial nephritis and silica nephropathy based on the result of electron microscopy-metal analysis. The previous physician initiated oral prednisolone (PSL) 30 mg/day along with a maximum of 100 mg/day of mizoribine and 75 mg/day of cyclosporine for suspected sarcoidosis, but kidney function progressively deteriorated over time. The patient presented to our department with sCr 1.8 mg/dL, eGFR 26.4 mL/min/1.73m². Gallium scintigraphy showed no significant uptake throughout the body, ruling out sarcoidosis. CT revealed idiopathic interstitial pneumonia immediately beneath the pleura in both lungs. A detailed medical history revealed that at age 17, the patient had hired contractors to renovate the walls and the ceiling of her bedroom at home with diatomaceous earth, and she continued to use that room as her bedroom during the construction period. As she had no occupational history potentially causing silicon exposure, silicon deposition in the kidney tissue was presumed to originate from silicon contained in the diatomaceous earth. Concurrently, silicosis was suspected as a possible cause of the interstitial pneumonia. Given the limited evidence regarding the efficacy of immunosuppressants for silicosis, PSL was tapered, and conservative management for CKD was continued.

Scanning electron microscopy confirmed that materials provided by the patient from her bedroom showed the characteristic structure typical of common diatomaceous earth. Fluorescence X-ray analysis revealed the material contained 39.6% silicon. While crystalline silicon tends to deposit in the lungs and amorphous silicon in the kidneys, powder X-ray diffraction analysis of the material in this case showed crystalline structure.

We present a case of silica nephropathy with kidney impairment over approximately 20 years, presumed to result from long-term exposure to diatomaceous earth at home. Structural and compositional analysis confirmed that the ceiling and wall materials in the patient's bedroom contained diatomaceous earth, which contains a certain amount of silicon. While diatomaceous earth is commonly used in households for its humidity control, deodorizing, and fire resistance, its safety should be reevaluated.