A 35-year-old man presents with haematuria, RBC casts in urine, hypertension, and declining GFR. Serum complement C3 is low, C4 is normal. ANCA is negative, ANA negative, anti-dsDNA negative. ASO titre is elevated. Renal biopsy shows diffuse endocapillary hypercellularity with 'humps' on electron microscopy. What is the diagnosis?
- A IgA nephropathy — mesangial IgA deposits
- B Membranoproliferative glomerulonephritis type I — mesangial and subendothelial deposits with tram-track GBM
- C Post-streptococcal glomerulonephritis (PSGN) — subepithelial humps (immune deposits) on EM ✓
- D Rapidly progressive GN due to anti-GBM disease
Correct answer: C. Post-streptococcal glomerulonephritis (PSGN) — subepithelial humps (immune deposits) on EM
Explanation
Post-streptococcal GN (PSGN) classically presents 1-3 weeks after streptococcal pharyngitis or 3-6 weeks after skin infection. Key features: low C3 (normal C4 — alternate pathway activation), positive ASO titre, and 'humps' (subepithelial electron-dense immune deposits) on EM — these are pathognomonic for PSGN. The complement pattern (C3 low, C4 normal) indicates alternative pathway activation, unlike lupus nephritis (both C3 and C4 low — classical pathway). IgA nephropathy has normal complement. MPGN type I causes a tram-track GBM appearance.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.