In a series of 150 Indian patients with biopsy-proven acute nephritic syndrome, which is the most common histological pattern observed on light microscopy?

Explanation

## Diffuse Proliferative Glomerulonephritis: The Most Common Histological Pattern ### Definition & Epidemiology **Key Point:** Diffuse proliferative glomerulonephritis (DPGN) is the most common histological pattern in acute nephritic syndrome, accounting for >70% of cases in Indian cohorts. It is the hallmark lesion of post-streptococcal glomerulonephritis. **High-Yield:** "Diffuse" means involvement of >50% of glomeruli; "proliferative" refers to increased cellularity (endocapillary proliferation). ### Light Microscopy Findings | Feature | Appearance | | --- | --- | | **Glomerular cellularity** | Increased (endothelial and mesangial cells) | | **Capillary lumens** | Narrowed, "bloodless" glomeruli | | **Basement membrane** | Intact (no breaks or crescents) | | **Interstitium** | Mild oedema, sparse inflammation | | **Tubules** | Epithelial flattening, RBC casts | ### Immunofluorescence Microscopy (IFM) **Key Point:** IFM is essential for diagnosis and shows: - **Granular deposits** of IgG, IgM, C3, and C1q along the glomerular basement membrane (GBM) - **Starry-sky pattern** — diffuse, fine granular staining - C3 dominance is characteristic of PSGN ### Electron Microscopy (EM) **Clinical Pearl:** EM reveals **subepithelial "humps"** — electron-dense deposits on the outer aspect of the GBM. These are pathognomonic for PSGN and distinguish it from other causes of DPGN (e.g., lupus, which has subendothelial and intramembranous deposits). ### Comparison with Other Patterns | Pattern | Prevalence in Acute Nephritic | Typical Cause | Prognosis | | --- | --- | --- | --- | | **Diffuse proliferative** | >70% | PSGN, lupus | Excellent (PSGN) | | **Focal proliferative** | ~15% | IgA nephropathy, PSGN variant | Variable | | **Membranous** | <5% | Chronic infections, autoimmune | Chronic proteinuria | | **Crescentic** | ~5% | ANCA-associated, anti-GBM | Poor without treatment | ### Clinical Correlation **High-Yield:** Patients with DPGN and acute nephritic syndrome typically: - Present with sudden haematuria, RBC casts, and hypertension - Have depressed serum complement (C3) at presentation - Recover renal function in >90% of cases (if PSGN) - Do NOT require immunosuppression in uncomplicated PSGN