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Difficulty: HardPathology and Biopsy Interpretation

An attending nephrologist is reviewing renal biopsy synoptic reports for five different patients presenting with various nephritic and nephrotic syndromes. Match each set of light microscopy (LM), immunofluorescence (IF), and electron microscopy (EM) findings with its corresponding definitive pathologic diagnosis.

  • LM: Segmental sclerosis and hyalinosis in some glomeruli. IF: Negative for specific immune complexes. EM: Diffuse podocyte foot process effacement without immune deposits.Focal segmental glomerulosclerosis (FSGS)
  • LM: Diffuse capillary and basement membrane thickening without prominent hypercellularity. IF: Granular IgG and C3 deposition. EM: Subepithelial immune complex deposits with 'spike and dome' appearance.Membranous nephropathy
  • LM: Hypercellular glomeruli with lobular accentuation and 'tram-track' appearance of the basement membrane. IF: Granular IgG and C3 deposition. EM: Large subendothelial immune complex deposits.Membranoproliferative glomerulonephritis (MPGN) Type I
  • LM: Enlarged, hypercellular glomeruli with prominent neutrophilic infiltration. IF: Granular IgG and C3 deposition in a 'starry sky' pattern. EM: Large, dome-shaped subepithelial electron-dense deposits ('humps').Postinfectious glomerulonephritis (PSGN)
  • LM: Mesangial hypercellularity and matrix expansion. IF: Prominent mesangial deposition of IgA and C3. EM: Electron-dense deposits located primarily within the mesangium.IgA nephropathy (Berger disease)

Answer

The correct matches pair the specific triad of biopsy findings to their respective diseases: 1 maps to FSGS, 2 to Membranous nephropathy, 3 to MPGN Type I, 4 to Postinfectious glomerulonephritis, and 5 to IgA nephropathy.
Renal biopsy interpretation fundamentally relies on a triad of diagnostic modalities. Electron microscopy pinpoints the exact ultrastructural location of the injury or deposits. Immunofluorescence determines the immunological mechanism by identifying specific antibodies. Light microscopy identifies the resultant structural damage. By synthesizing these three modalities, each set of biopsy findings pathognomonically matches one specific glomerulopathy.

Step-by-Step Solution

1
Analyze the exact ultrastructural location of the immune deposits on Electron Microscopy (EM) for each biopsy.
Deposits are identified as absent (Item 1), subepithelial with spikes (Item 2), subendothelial (Item 3), subepithelial humps (Item 4), or mesangial (Item 5).
The precise location of electron-dense deposits on EM is the most specific feature for differentiating primary glomerulopathies.
2
Correlate the EM findings with Immunofluorescence (IF) patterns.
Item 5 is uniquely characterized by IgA, confirming IgA nephropathy. Item 1 is negative, confirming a non-immune process (FSGS). The remaining items show varying granular IgG/C3 patterns.
IF identifies the specific immunoglobulins involved, which is diagnostic for diseases like IgA nephropathy or anti-GBM disease (not listed here), and helps rule out immune-mediated injury when negative.
3
Evaluate the Light Microscopy (LM) architectural changes.
Thickening ('spike and dome') confirms Membranous nephropathy (Item 2); 'tram-tracking' confirms MPGN Type I (Item 3); and neutrophilic hypercellularity confirms Postinfectious GN (Item 4).
Light microscopy findings reflect the distinct cellular reactions and basement membrane remodeling triggered by the specific immune deposits.

Key Concept

Definitive interpretation of medical renal biopsies requires the integration of Light Microscopy (architectural changes), Immunofluorescence (type of immune deposits), and Electron Microscopy (ultrastructural location of deposits).
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Pathology and Biopsy Interpretation

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