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Difficulty: HardPathology and Biopsy Interpretation

A 4848-year-old African American man presents with a 33-week history of progressive lower extremity edema, facial swelling, and frothy urine. He has a history of well-controlled hypertension. Vital signs show a blood pressure of 142/88142/88 mmHg. Laboratory studies reveal a serum creatinine of 1.41.4 mg/dL, serum albumin of 2.12.1 g/dL, and a 2424-hour urine protein excretion of 7.27.2 g. Serologic workup for HIV, hepatitis B, and hepatitis C is negative. A percutaneous renal biopsy is performed, yielding a core of tissue containing 1212 glomeruli. Light microscopy reveals normal glomerular architecture with thin capillary walls and no evidence of segmental sclerosis, crescent formation, or hypercellularity. Immunofluorescence is negative for all immunoglobulins and complement components. Electron microscopy demonstrates extensive, diffuse effacement of podocyte foot processes with no electron-dense deposits. The synoptic pathology report explicitly notes that the biopsy specimen consists entirely of superficial cortical tissue and completely lacks juxtamedullary glomeruli. Based on these specific biopsy limitations, which of the following pathologic diagnoses is at the highest risk of being erroneously excluded due to a sampling artifact?

  1. A
    Minimal change disease
  2. B
    Membranous nephropathy
  3. Focal segmental glomerulosclerosisAnswer
  4. D
    IgA nephropathy
  5. E
    AL amyloidosis

Answer

Focal segmental glomerulosclerosis
The correct diagnosis at highest risk of being falsely excluded is Focal segmental glomerulosclerosis (FSGS). FSGS is a major cause of nephrotic syndrome in adults, and the risk is disproportionately high in patients of African descent (often linked to APOL1 risk alleles). The defining pathologic hallmark of FSGS is segmental sclerosis and hyalinosis of some, but not all, glomeruli (a 'focal' distribution). Crucially, in the early stages of the disease, these sclerotic lesions are topographically restricted to the juxtamedullary glomeruli (those situated deepest in the cortex, adjacent to the medulla). The superficial cortical glomeruli typically remain structurally normal on light microscopy and show only diffuse podocyte foot process effacement on electron microscopy. Because this patient's biopsy specimen contains only superficial cortical tissue, it is anatomically inadequate for ruling out FSGS. If the clinician accepts these superficial findings without acknowledging the critical sampling artifact described in the pathology report, FSGS will be erroneously excluded, and the patient will be misdiagnosed with minimal change disease.

Step-by-Step Solution

1
Analyze the patient's clinical presentation.
The patient has new-onset nephrotic syndrome (massive proteinuria >3.5>3.5 g/day, hypoalbuminemia, and edema) and is an African American male.
Identifying the clinical syndrome and demographics places him at high risk for certain primary podocytopathies.
2
Interpret the stated biopsy findings.
Light microscopy and immunofluorescence are completely normal; electron microscopy shows only diffuse foot process effacement.
These specific findings perfectly match minimal change disease, but they also describe the 'normal-appearing' (non-sclerotic) glomeruli seen in other conditions.
3
Evaluate the adequacy and limitations of the biopsy specimen as reported.
The pathologist noted the sample contains only superficial cortical tissue, missing the juxtamedullary region.
Pathology interpretation requires correlating structural findings with anatomic adequacy.
4
Synthesize the findings to determine which disease is masked by this limitation.
Because early focal segmental glomerulosclerosis selectively involves the deep juxtamedullary glomeruli, a superficial biopsy can easily miss the defining sclerotic lesions.
This confirms that focal segmental glomerulosclerosis is the diagnosis at highest risk of being erroneously excluded (falsely assumed to be minimal change disease).

Key Concept

Focal segmental glomerulosclerosis (FSGS) initially affects juxtamedullary glomeruli; therefore, a renal biopsy lacking deep cortical tissue is subject to a sampling artifact that can lead to a false-negative result and an erroneous diagnosis of minimal change disease.
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Topics

Pathology and Biopsy Interpretation

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