Definition, Etiology & Clinical Presentation

Question	Answer
1. What is Acute Nephritic Syndrome?	Acute nephritic syndrome is a clinical constellation of abrupt onset characterized by: 1) Macroscopic or microscopic glomerular hematuria (dysmorphic RBCs and RBC casts). 2) Oliguria (decreased urine output). 3) Systemic Hypertension (fluid overload and renin-angiotensin activation). 4) Edema (predominantly periorbital and facial, non-dependent). 5) Decreased GFR with elevated BUN and serum creatinine.
2. What are the nephritogenic strains of Group A Beta-Hemolytic Streptococcus (GABHS)?	- Throat / Pharyngitis strains: GABHS M types 1, 4, 12, 25 (latent period 1 to 2 weeks). - Skin / Pyoderma strains: GABHS M types 2, 49, 55, 57, 60 (latent period 3 to 6 weeks). Pathogenic Antigens: Nephritis-Associated Plasmin Receptor (NAPlr) and Streptococcal Pyrogenic Exotoxin B (SPEB), which deposit in the glomerular subepithelial space and activate the alternative complement pathway.
3. Why does urine appear cola-colored or smoky in PSGN?	Under acidic and concentrated urinary conditions within the renal tubules, filtered erythrocytes undergo lysis and oxidation. Hemoglobin is oxidized to acid hematin (methemoglobin), imparting the characteristic brownish-black, cola, smoky, or tea color. The absence of clots confirms that bleeding originates from glomerular capillaries rather than lower urinary tracts.
4. Contrast the edema of Nephritic Syndrome from Nephrotic Syndrome.
5. VIVA TRAP: Can early antibiotic treatment of streptococcal pharyngitis or impetigo prevent PSGN?	- Pharyngitis: Early penicillin treatment of streptococcal pharyngitis PREVENTS Acute Rheumatic Fever (ARF), but has NO proven protective effect in preventing PSGN once the nephritogenic strain has infected the host. - Pyoderma: Early antibiotic therapy clears cutaneous colonization and prevents transmission to contacts, but does not reliably prevent PSGN. Examiner Counter-Question: Then why give penicillin in acute PSGN? To eradicate nephritogenic streptococcal carriage and prevent spread to family members and school contacts!

Diagnostics & Laboratory Findings

Question	Answer
6. What is the diagnostic hallmark on urine routine microscopy in PSGN?	Red Blood Cell (RBC) Casts and Dysmorphic Erythrocytes ($>80\%$). - RBC casts are cylindrical moulds formed in the distal convoluted tubules and collecting ducts when erythrocytes become trapped within precipitating Tamm-Horsfall mucoprotein. Their presence is pathognomonic of acute glomerular injury and capillary basement membrane disruption.
7. Describe the complement profile in PSGN. Which pathway is activated?	In PSGN, the Alternative Complement Pathway is activated by streptococcal antigens (NAPlr, SPEB): - Serum Complement C3: Markedly depressed ($<30\text{ mg/dL}$) in $>90\%$ of cases during the first 2 weeks. - Serum Complement C4: Normal (normal C4 differentiates PSGN from Classic Pathway-mediated conditions like SLE and Cryoglobulinemia where both C3 and C4 are depressed).
8. VIVA TRAP: The "C3 Rule": When MUST serum C3 normalize in PSGN?	Serum C3 levels MUST return to normal within 8 to 12 weeks from disease onset. MANDATORY VIVA TRAP: If serum C3 remains depressed beyond 12 weeks, a Renal Biopsy is mandatory to rule out Membranoproliferative Glomerulonephritis (MPGN), C3 Glomerulopathy, or Lupus Nephritis.
9. Compare ASO Titer with Anti-DNase B in post-pharyngitic vs post-pyodermal PSGN.	- ASO (Antistreptolysin O) Titer: Highly elevated ($>80\%$) following pharyngitis, but elevated in only $50\%$ of post-pyodermal cases (lipids in sebum inactivate streptolysin O antigenicity). - Anti-DNase B (Deoxyribonuclease B): Elevated in $>90-95\%$ of cases following streptococcal skin infections / pyoderma. - Streptozyme Test: Screens for 5 streptococcal antibodies (ASO, Anti-DNase B, Antihyaluronidase, Antistreptokinase, Anti-NADase); $>95\%$ sensitive.
10. What are the typical Light, Immunofluorescence, and Electron Microscopic findings in PSGN?	- Light Microscopy: Diffuse endocapillary proliferative glomerulonephritis with neutrophilic infiltration ("exudative GN") causing occlusion of capillary lumina; enlarged, hypercellular glomeruli. - Immunofluorescence (IF): Coarse, granular capillary loop and mesangial deposits of IgG and C3 ("starry sky" or "garland" pattern). - Electron Microscopy (EM): Classical pathognomonic large, dome-shaped subepithelial electron-dense "humps".

Management of Hypertensive Emergency & Complications

Question	Answer
11. Define Hypertensive Emergency in pediatric PSGN and detail its immediate management.	- Definition: Blood pressure $\ge 95^{\text{th}}\text{ centile} + 12\text{ mmHg}$ (or Stage 2 HTN) accompanied by acute end-organ damage: headache, projectile vomiting, blurred vision, encephalopathy, seizures, or acute pulmonary edema. - Target Reduction: Lower Mean Arterial Pressure (MAP) by $20-25\%$ over the first 6 to 8 hours, then gradually normalize over 24 to 48 hours to avoid watershed cerebral ischemia. - Intravenous Pharmacotherapy: 1) IV Labetalol: $0.2-0.5\text{ mg/kg}$ IV push over 5 minutes; if needed, infusion at $0.25-1.0\text{ mg/kg/hour}$. 2) IV Nicardipine / Sodium Nitroprusside: Alternative continuous infusions. 3) Loop Diuretic: IV Furosemide at $2.0-4.0\text{ mg/kg}$ IV push. Since hypertension is volume-mediated, furosemide diuresis is the most physiological and rapid intervention.
12. VIVA TRAP: Why are ACE Inhibitors (Enalapril / Captopril) contraindicated during the acute oliguric phase of PSGN?	In acute oliguric PSGN, GFR is acutely compromised, and hyperkalemia is a life-threatening risk. ACE inhibitors dilate the efferent glomerular arteriole, precipitously dropping intraglomerular hydrostatic filtration pressure, worsening acute kidney injury, and impairing aldosterone-mediated potassium excretion, triggering fatal hyperkalemia!
13. What is the fluid calculation in an oliguric child with PSGN?	Strict fluid restriction using the formula: $$\text{Total 24-hr Fluid Allowance} = \text{Insensible Water Loss } (400\text{ mL/m}^2/\text{day}) + \text{Previous 24-hr Urine Output} + \text{Extra losses (vomitus)}$$ Administer as $5\%$ or $10\%$ Dextrose in water or $0.45\%$ normal saline without potassium.
14. What are the urgent indications for Dialysis (Renal Replacement Therapy) in PSGN?	1) Refractory Hyperkalemia: Serum $K^+ > 6.5\text{ mEq/L}$ with ECG changes unresponsive to medical stabilization. 2) Severe Fluid Overload / Pulmonary Edema: Refractory to high-dose IV furosemide. 3) Uremic Encephalopathy or Pericarditis. 4) Severe Intractable Metabolic Acidosis: $pH < 7.15, HCO_3^- < 10\text{ mEq/L}$.
15. Counter-Question Chain: "What is the expected resolution timeline of various features in PSGN?"	1) Diuresis: Begins within 5 to 10 days. 2) Hypertension & Edema: Normalizes in 2 to 4 weeks. 3) Gross Hematuria: Resolves within 1 to 3 weeks. 4) Serum C3 Complement: Normalizes within 8 to 12 weeks. 5) Proteinuria: Non-nephrotic proteinuria resolves in 6 months. 6) Microscopic Hematuria: Can persist normally for up to 1 to 2 years (reassure parents!).