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Difficulty: EasyPathology and Biopsy Interpretation

A 45-year-old man presents to the clinic for the evaluation of progressive lower extremity swelling over the past three weeks. He has no significant past medical history and takes no medications. Vital signs are within normal limits. Physical examination demonstrates marked bilateral pitting edema extending to the knees. Laboratory evaluation reveals a serum albumin level of 2.2 g/dL and a serum creatinine of 0.8 mg/dL. Urinalysis demonstrates 4+ proteinuria with no hematuria or cellular casts. A 24-hour urine collection confirms 6.8 g of protein. A percutaneous renal biopsy is performed to establish the diagnosis. Light microscopy shows uniform, diffuse thickening of the glomerular capillary walls without an increase in cellularity. Jones methenamine silver staining highlights projections of basement membrane material, creating a "spike and dome" appearance. Immunofluorescence demonstrates a diffuse granular pattern of IgG and C3 deposition along the capillary loops. Which of the following is the most likely diagnosis?

  1. Membranous nephropathyAnswer
  2. B
    Minimal change disease
  3. C
    Focal segmental glomerulosclerosis
  4. D
    IgA nephropathy
  5. E
    Diabetic nephropathy

Answer

Membranous nephropathy
The correct answer accurately synthesizes the classic clinical presentation of nephrotic syndrome in an adult with the pathognomonic histologic features of membranous nephropathy. The "spike and dome" appearance on Jones methenamine silver stain is a highly specific finding caused by the glomerular basement membrane growing upward between subepithelial immune complex deposits. This is confirmed by the granular pattern of IgG and C3 on immunofluorescence.

Step-by-Step Solution

1
Identify the primary clinical syndrome.
The patient has heavy proteinuria (>3.5 g/day), hypoalbuminemia, and severe edema, which defines nephrotic syndrome.
Establishing the clinical syndrome narrows the differential diagnosis to etiologies of nephrotic syndrome rather than nephritic syndrome.
2
Analyze the light microscopy findings.
Thickened glomerular capillary walls without hypercellularity are observed.
This points toward a non-proliferative etiology of glomerular injury.
3
Interpret the specialized stain and immunofluorescence results.
Silver stain shows a "spike and dome" appearance; immunofluorescence shows granular IgG and C3.
The "spike and dome" pattern represents basement membrane growing around subepithelial immune complexes, which are confirmed to be IgG and C3 by immunofluorescence.
4
Synthesize findings to formulate a definitive diagnosis.
The combination of adult-onset nephrotic syndrome and these exact histopathologic features confirms membranous nephropathy.
These findings are unique and pathognomonic for this specific glomerular disease.

Key Concept

The characteristic histopathologic findings of membranous nephropathy include diffuse glomerular basement membrane thickening, a "spike and dome" appearance on silver stain, and granular subepithelial deposits of IgG and C3 on immunofluorescence.
Estimated Time:50s
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Topics

Pathology and Biopsy Interpretation

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