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Difficulty: HardNephrology

Match each patient's clinical presentation and initial diagnostic findings with the most accurate underlying pathophysiologic mechanism or defining etiology.

  • A 35-year-old man with hemoptysis, rapidly worsening renal function, and linear IgG deposits along the glomerular basement membrane on immunofluorescence.Autoantibodies directed against the non-collagenous domain of the alpha-3 chain of type IV collagen.
  • A 22-year-old man with sensorineural hearing loss, microscopic hematuria, and a 'basket-weave' appearance of the glomerular basement membrane on electron microscopy.Genetic mutation in type IV collagen chains leading to defective structural assembly of the basement membrane.
  • A 45-year-old woman with chronic hepatitis C presenting with palpable purpura, arthralgias, and laboratory findings showing profoundly low C4 but normal C3 complement levels.Deposition of cold-precipitable immune complexes containing rheumatoid factor, leading to classical complement pathway activation.
  • A 12-year-old boy with periorbital edema, gross hematuria, and subepithelial electron-dense 'humps' on renal biopsy two weeks after recovering from impetigo.Immune complex deposition characterized by alternate complement pathway activation, producing decreased C3 with typically normal C4.
  • A 28-year-old patient of African descent with untreated HIV presenting with massive edema, heavy proteinuria, and glomerular tuft collapse on biopsy.Severe podocyte injury and depletion, frequently associated with viral pathogenesis and specific genetic risk alleles like APOL1.

Answer

The correct matches map Goodpasture syndrome to autoantibodies against the alpha-3 chain of type IV collagen; Alport syndrome to genetic mutations in type IV collagen assembly; Mixed cryoglobulinemia to cold-precipitable immune complexes with classical complement activation; Poststreptococcal glomerulonephritis to alternate complement pathway activation; and Collapsing FSGS to viral-associated podocyte injury linked to APOL1.
Each clinical vignette contains pathognomonic markers for a specific glomerular disease. Identifying the precise pattern of complement consumption, genetic history, or specific immunofluorescence findings allows for accurate matching to the underlying pathophysiology.

Step-by-Step Solution

1
Analyze the immunofluorescence, complement levels, and demographic clues in each vignette.
Identified five distinct glomerular syndromes: Anti-GBM disease, Alport syndrome, Cryoglobulinemia, PSGN, and Collapsing FSGS.
Accurate diagnosis of nephritic and nephrotic syndromes requires integrating clinical history with specific biopsy and serologic findings.
2
Differentiate between the two diseases involving type IV collagen.
Linked the patient with hemoptysis to autoimmune destruction (Goodpasture) and the patient with hearing loss to genetic structural defects (Alport).
Both conditions involve type IV collagen, but their mechanisms (autoimmune vs. congenital mutation) dictate vastly different clinical presentations.
3
Differentiate between the causes of hypocomplementemia.
Linked the Hepatitis C patient with low C4 to classical pathway activation (Cryoglobulinemia) and the post-impetigo patient to alternate pathway activation (PSGN).
Complement profiling (C3 vs. C4 levels) is a critical step in narrowing down the differential diagnosis for immune complex glomerulonephritis.

Key Concept

Pathophysiological mechanisms and histopathological correlates of primary and secondary glomerular diseases.
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Topics

Nephrology

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