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Thin basement membrane nephropathy cannot be diagnosed reliably in deparaffinized, formalin-fixed tissue
Samih H Nasr1, Glen S Markowitz, Anthony M Valeri
1Department of Pathology, Columbia University, College of Physicians and Surgeons, 630 West 168th Street, VC14-224, New York, NY 10032, USA. sn386@columbia.edu
Abstract:
In diagnostic renal pathology, electron microscopy is ideally performed on glutaraldehyde-fixed, plastic resin-embedded tissue (EM-G). When no glomeruli are present in the portion of the biopsy fixed in glutaraldehyde, formalin-fixed, paraffin-embedded tissue can be reprocessed for electron microscopy (EM-F). The usefulness of this salvage technique for the diagnosis of thin basement membrane nephropathy (TBMN) has not been studied systematically. Here we compare the glomerular basement membrane (GBM) thickness by EM-G vs EM-F in 21 renal biopsies, including TBMN (eight patients), normals (two patients), minimal change disease (MCD) (six patients) and diabetic nephropathy (DN) (five patients). There was significant reduction of the GBM thickness by EM-F compared with EM-G across all diagnostic categories in all 21 cases. The mean percentage reduction in GBM thickness was 23% for the TBMN cases, 40% for the normal/MCD cases and 34% for the DN cases. Four patients with MCD had a mean GBM thickness by EM-F that fell below the defining threshold for diagnosis of TBMN. For the TBMN cases, the 99th percentile for GBM thickness by EM-F was 194 nm, suggesting that the diagnosis of TBMN by EM-F can be excluded with confidence if the GBM thickness is above 200 nm. No clear criteria could be established to diagnose TBMN by EM-F. Renal pathologists should be aware that reprocessing of paraffin tissue for EM causes artifactual GBM thinning that precludes accurate diagnosis of TBMN.
Insights
Reprocessing formalin-fixed tissue for electron microscopy (EM-F) causes artifactual thinning of the glomerular basement membrane (GBM). This technique is unreliable for diagnosing thin basement membrane nephropathy (TBMN).
Area of Science:
- Renal Pathology
- Diagnostic Techniques
- Electron Microscopy
Background:
- Electron microscopy (EM) is crucial for diagnosing renal pathologies, typically using glutaraldehyde-fixed tissue (EM-G).
- When glomeruli are absent in EM-G samples, formalin-fixed, paraffin-embedded tissue (EM-F) can be reprocessed as a salvage technique.
- The diagnostic utility of EM-F for thin basement membrane nephropathy (TBMN) remains uninvestigated.
Purpose of the Study:
- To systematically evaluate the usefulness of reprocessing formalin-fixed, paraffin-embedded tissue (EM-F) for diagnosing thin basement membrane nephropathy (TBMN).
- To compare glomerular basement membrane (GBM) thickness measurements obtained by EM-F versus standard glutaraldehyde-fixed electron microscopy (EM-G).
Main Methods:
- Compared GBM thickness in 21 renal biopsies using both EM-G and EM-F.
- Biopsies included cases of TBMN, normal controls, minimal change disease (MCD), and diabetic nephropathy (DN).
- Analyzed GBM thickness reduction and diagnostic thresholds between the two EM preparation methods.
Main Results:
- EM-F demonstrated a significant reduction in GBM thickness across all diagnostic categories compared to EM-G.
- Mean GBM thickness reduction was 23% for TBMN, 40% for normal/MCD, and 34% for DN cases.
- Four MCD cases showed mean GBM thickness below the TBMN diagnostic threshold using EM-F; TBMN diagnosis by EM-F was unreliable, with a 99th percentile of 194 nm.
Conclusions:
- Reprocessing formalin-fixed tissue for electron microscopy (EM-F) introduces artifactual GBM thinning.
- This artifactual thinning precludes accurate diagnosis of thin basement membrane nephropathy (TBMN).
- Renal pathologists must be aware that EM-F is unsuitable for TBMN diagnosis due to unreliable GBM thickness measurements.
