A 58-year-old man with hepatitis C infection develops nephrotic syndrome, hematuria, and hypocomplementemia (low C3 and C4). Renal biopsy shows mesangial and subendothelial immune deposits with a 'tram-track' appearance on silver stain due to mesangial interposition. Immunofluorescence reveals IgM and C3 deposits. The most likely diagnosis is:
- A Type I membranoproliferative glomerulonephritis (MPGN) ✓
- B IgA nephropathy
- C Anti-GBM disease
- D Focal segmental glomerulosclerosis
Correct answer: A. Type I membranoproliferative glomerulonephritis (MPGN)
Explanation
Type I MPGN (now reclassified as immune complex-mediated MPGN) is strongly associated with HCV-induced cryoglobulinemia. The mesangial and subendothelial deposits activate complement classically (low C3 and C4), and mesangial cell interposition creates the double-contour 'tram-track' appearance on silver/PAS stain. IgM deposits reflect cryoglobulins. Type II MPGN (dense deposit disease) shows C3 nephritic factor (C3NeF) activating the alternative pathway (low C3, normal C4) and electron-dense deposits within the GBM. Anti-GBM disease shows linear IgG on IF.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.