## Distinguishing Features of Post-Streptococcal GN **Key Point:** PSGN is characterized by immune complex deposition (IgG and IgM, NOT IgA) and distinctive electron microscopic findings. ### Immunofluorescence Pattern in PSGN - **Granular deposits** of IgG and IgM along the glomerular basement membrane and mesangium - **NOT IgA-dominant** — IgA-dominant deposits are the hallmark of IgA nephropathy (Berger disease), a different entity - C3 deposits are prominent (C3-dominant pattern) ### Electron Microscopy: Pathognomonic Finding - **Subepithelial "humps"** — large electron-dense deposits between the GBM and podocytes - These humps are virtually diagnostic of PSGN and distinguish it from other nephritic GN ### Histology - Endocapillary proliferation (increased cellularity within capillary loops) - Extracapillary proliferation (crescent formation) — present in severe cases - Acute tubular necrosis may occur ### Clinical Course in Children - Hematuria and hypertension typically resolve within **1–2 weeks** - Urinary abnormalities may persist for months but eventually clear - Excellent prognosis in children; adults have higher risk of progression **High-Yield:** The combination of **subepithelial humps + IgG/IgM/C3 deposits + clinical history of streptococcal infection** is diagnostic of PSGN. IgA-dominant staining points away from PSGN and toward IgA nephropathy. **Clinical Pearl:** PSGN is the most common acute GN in children worldwide, especially in low-income countries with high streptococcal infection burden. | Feature | PSGN | IgA Nephropathy | | --- | --- | --- | | **IF pattern** | IgG/IgM/C3 (granular) | IgA-dominant | | **EM finding** | Subepithelial humps | Mesangial deposits | | **Trigger** | Post-streptococcal | Mucosal infection (IgA1 overproduction) | | **Prognosis (children)** | Excellent | Variable; some progress |
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