A 28-year-old man presents with sudden-onset hematuria, hypertension, and mild renal dysfunction 10 days after a throat infection. Serum complement C3 levels are low. A renal biopsy shows subepithelial 'humps' on electron microscopy. Which feature best distinguishes post-streptococcal glomerulonephritis (PSGN) from IgA nephropathy in this clinical context?

Question

Accepted Answer

A. Subepithelial electron-dense deposits ('humps') on electron microscopy. ## Distinguishing PSGN from IgA Nephropathy

### Electron Microscopy Findings

**Key Point:** Subepithelial electron-dense deposits ('humps') are pathognomonic for post-streptococcal glomerulonephritis and are absent in IgA nephropathy.

### Comparison Table

| Feature | PSGN | IgA Nephropathy |
|---------|------|------------------|
| **EM deposits** | Subepithelial 'humps' (pathognomonic) | Mesangial, intramembranous, subendothelial |
| **IF pattern** | IgG, C3 (granular) | IgA dominant (mesangial) |
| **C3 levels** | Low (transient) | Normal |
| **Onset** | Post-infectious (2–3 weeks) | Insidious, often asymptomatic |
| **Prognosis** | Usually self-limited | Progressive in 20–30% |

### Why This Matters

**High-Yield:** The 'hump' appearance on electron microscopy is virtually diagnostic of PSGN and does not occur in IgA nephropathy. This finding, combined with low C3 and post-streptococcal history, clinches PSGN.

**Clinical Pearl:** PSGN typically resolves spontaneously within 6–8 weeks, whereas IgA nephropathy follows a chronic course with progressive renal decline in a subset of patients.

### Why Other Options Are Incorrect

- **Option 0 (IgA deposits):** IgA deposits are the hallmark of IgA nephropathy, NOT PSGN. PSGN shows IgG and C3 predominance.
- **Option 2 (Hematuria):** Both PSGN and IgA nephropathy present with hematuria; this is not discriminatory.
- **Option 3 (Demographics):** Both conditions can present in young males; age and sex are not distinguishing features.

Answer

B. Presence of IgA deposits on immunofluorescence

Answer

C. Male predominance and young age at presentation

Answer

D. Hematuria as the presenting symptom

Explanation

Distinguishing PSGN from IgA Nephropathy

Electron Microscopy Findings

Comparison Table

Why This Matters

Why Other Options Are Incorrect

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Feature	PSGN	IgA Nephropathy
EM deposits	Subepithelial 'humps' (pathognomonic)	Mesangial, intramembranous, subendothelial
IF pattern	IgG, C3 (granular)	IgA dominant (mesangial)
C3 levels	Low (transient)	Normal
Onset	Post-infectious (2–3 weeks)	Insidious, often asymptomatic
Prognosis	Usually self-limited	Progressive in 20–30%