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Comparison of Ultrastructural Features Between Patients with Mercury-associated Membranous Nephropathy and Idiopathic
Ai-Bo Qin1, Zi-Shan Lin1, Su-Xia Wang2
1Renal 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.
Background:
Prolonged 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.
Methods:
We 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.
Results:
Compared 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%).
Conclusions:
Foot 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.
Insights
Mercury-associated membranous nephropathy (M-MN) presents with less severe podocyte damage and better prognosis compared to idiopathic membranous nephropathy (I-MN). Distinguishing M-MN involves analyzing foot process width (FPW) and electron-dense deposits.
Area of Science:
- Nephrology
- Toxicology
- Pathology
Background:
- Prolonged mercury exposure is a known cause of membranous nephropathy (MN).
- Mercury-associated MN (M-MN) and idiopathic MN (I-MN) share similar clinical features, increasing the risk of misdiagnosis.
- Clinicopathological and ultrastructural differences between M-MN and I-MN require detailed investigation.
Purpose of the Study:
- To compare the clinicopathological and ultrastructural characteristics of M-MN and I-MN.
- To identify distinguishing features that aid in differentiating M-MN from I-MN.
- To evaluate the prognostic implications of these differences.
Main Methods:
- Retrospective analysis of 13 M-MN and 13 I-MN patients.
- Evaluation of electron micrographs of glomerular capillaries.
- Calculation of foot process width (FPW) and foot processes per 10 μm glomerular basement membrane (GBM).
- Assessment of electron-dense deposit presence and location.
Main Results:
- M-MN patients were younger and achieved remission faster with lower relapse rates than I-MN patients.
- M-MN showed significantly lower FPW and more foot processes per 10 μm GBM compared to I-MN.
- A higher incidence of mesangial electron-dense deposits was observed in M-MN.
- A foot process width cutoff of <1654 nm effectively differentiated M-MN from I-MN with high sensitivity and specificity.
Conclusions:
- Membranous nephropathy in mercury-exposed individuals exhibits less severe foot process effacement than I-MN.
- Less severe podocyte damage in M-MN suggests mercury as the causative agent.
- The better prognosis observed in M-MN may be attributed to less severe podocyte injury.
