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Difficulty: MediumPathology and Biopsy Interpretation

A 3232-year-old man presents to the emergency department with a 33-day history of coughing up blood-tinged sputum, fatigue, and decreased urine output. His temperature is 37.2∘37.2^\circ C (99∘99^\circ F), blood pressure is 155/95155/95 mm Hg, and pulse is 9292/min. Lung auscultation reveals bilateral crackles. Laboratory studies show a serum creatinine of 3.83.8 mg/dL and blood urea nitrogen of 4545 mg/dL. Urinalysis reveals 3+ blood, 1+ protein, and numerous dysmorphic red blood cells with red blood cell casts. A percutaneous renal biopsy is performed. Light microscopy shows cellular crescents in 60%60\% of the glomeruli. Immunofluorescence microscopy demonstrates smooth, continuous, ribbon-like linear deposition of IgG and C3 along the glomerular basement membranes. Which of the following is the most likely diagnosis?

  1. A
    Granulomatosis with polyangiitis
  2. B
    IgA nephropathy
  3. C
    Lupus nephritis
  4. Anti-glomerular basement membrane diseaseAnswer
  5. E
    Poststreptococcal glomerulonephritis

Answer

Anti-glomerular basement membrane disease
The correct answer is anti-glomerular basement membrane (anti-GBM) disease, also known as Goodpasture disease. The clinical presentation of hemoptysis and acute kidney injury with red blood cell casts suggests a pulmonary-renal syndrome. The renal biopsy is diagnostic. Light microscopy shows crescentic glomerulonephritis, which corresponds clinically to rapidly progressive glomerulonephritis (RPGN). Crucially, immunofluorescence microscopy demonstrates a smooth, linear deposition of IgG along the glomerular basement membrane. This specific immunofluorescence pattern is caused by autoantibodies targeting the noncollagenous domain of the alpha-3 chain of type IV collagen and is pathognomonic for anti-GBM disease.

Step-by-Step Solution

1
Analyze the clinical presentation.
The patient has a pulmonary-renal syndrome, evidenced by hemoptysis (alveolar hemorrhage) and acute nephritic syndrome (hypertension, elevated creatinine, hematuria with red blood cell casts).
Identifying the clinical syndrome narrows the differential diagnosis of glomerulonephritis to specific entities that affect both lungs and kidneys.
2
Interpret the light microscopy findings from the renal biopsy.
The presence of cellular crescents in 60%60\% of glomeruli indicates a rapidly progressive glomerulonephritis (RPGN).
RPGN requires urgent diagnosis and treatment, and is typically categorized into three types based on immunofluorescence patterns.
3
Interpret the immunofluorescence microscopy findings.
The biopsy shows continuous, linear deposition of IgG and C3 along the glomerular basement membranes.
Linear immunofluorescence is pathognomonic for Type 1 RPGN (anti-glomerular basement membrane disease), distinguishing it from immune complex-mediated (granular IF) and pauci-immune (negative IF) forms.

Key Concept

The definitive diagnosis of anti-glomerular basement membrane (anti-GBM) disease requires interpreting the classic renal biopsy finding of continuous, linear IgG deposition along the glomerular basement membrane on immunofluorescence.
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Topics

Pathology and Biopsy Interpretation

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