• Ai-Bo Qin, Zi-Shan Lin, Su-Xia Wang, Hui Wang, Zhao Cui, Fu-de Zhou, and Ming-Hui Zhao.
• Renal Division, Department of Medicine, Peking University First Hospital, Renal Pathology Center, Institute of Nephrology, Peking University, Key Laboratory of Renal Disease, Ministry of Health of China, Key Laboratory of CKD Prevention and Treatment, Ministry of Education of China, Research Units of Diagnosis and Treatment of Immune-mediated Kidney Diseases, Chinese Academy of Medical Sciences, Beijing, China.
• Am. J. Med. Sci. 2021 Mar 1; 361 (3): 327-335.

BackgroundProlonged exposure to mercury can cause membranous nephropathy. Mercury-associated membranous nephropathy (M-MN) and idiopathic membranous nephropathy (I-MN) have similar clinical manifestations, making misdiagnoses likely. We compared the clinicopathological and ultrastructural features of M-MN and I-MN.MethodsWe retrospectively analyzed the clinicopathological data of 13 M-MN patients and 13 I-MN patients. Electron micrographs of glomerular capillaries were taken, and foot process width (FPW) and the number of foot processes per 10 μm glomerular basement membrane (GBM) were calculated. The presence and location of electron-dense deposits were recorded.ResultsCompared with I-MN patients, M-MN patients were younger (38.7 ± 8.5 versus 45.8 ± 5.7 years, P = 0.020), achieved complete remission more quickly (9.0 ± 6.1 versus 20.3 ± 9.8 months, P = 0.004), and had a lower relapse rate (0 versus 45.5%, P = 0.014). Patients with M-MN also had lower FPW (974.3 [interquartile range or IQR, 791.2-1504.4] nm versus 2370.6 [IQR, 2219.4-2559.1] nm, P = 0.001), more foot processes per 10 μm GBM (8.1 [IQR, 5.2-10.0] versus 3.3 [IQR, 3.1-3.5], P = 0.001), and a higher rate of mesangial electron-dense deposits (41.7% versus 0, P = 0.015). A cut-off FPW of <1654 nm differentiated M-MN from I-MN with high sensitivity (92.3%) and specificity (83.3%).ConclusionsFoot process effacement was less severe in M-MN than in I-MN. In patients with mercury toxic exposure, MN with less severe foot processes effacement suggested mercury could be the cause. Better prognosis in patients with M-MN may be associated with minor podocyte damage.Copyright © 2020 Southern Society for Clinical Investigation. Published by Elsevier Inc. All rights reserved.

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