Ch05: Nephrology — Nephrotic Syndrome, APSGN, UTI

Preparatory Mindset

Paediatric nephrology in this syllabus covers nephrotic syndrome (NS), acute post-streptococcal glomerulonephritis (APSGN), and urinary tract infection (UTI) — three very different diseases that all present with urine abnormalities. The mindset:

• Nephrotic syndrome: heavy proteinuria (>40 mg/m²/h or urine protein/creatinine >200 mg/mmol), hypoalbuminaemia (<25 g/L), oedema, hyperlipidaemia — minimal change disease is >85% in children → steroid-responsive (>90% respond to prednisolone) → relapses common but benign long-term. Complications: infection, thrombosis, steroid side effects.
• APSGN: haematuria (cola-coloured urine), hypertension, oedema, oliguria, ↓C3, ↑ASO, 1-3 weeks post-strep infection — management is supportive (BP control, fluid/salt restriction); prognosis excellent in children; C3 normalises in 6-8 weeks (persistent ↓C3 → think MPGN/Lupus).
• UTI: the "occult fever" of infants — fever without focus in a young child → urinalysis + culture; vesicoureteral reflux (VUR) is the main risk factor for renal scarring; treat promptly (oral/IV antibiotics), investigate after first febrile UTI in young children (USS ± DMSA ± MCUG).

The exam pearl: NS = protein-losing kidney (oedema, low albumin); APSGN = inflamed glomerulus (blood + hypertension); UTI = ascending infection (fever + pyuria).

Core Concepts

1. Nephrotic syndrome (NS)

Definition (the tetrad):

1. Proteinuria — >40 mg/m²/h or urine protein/creatinine >200 mg/mmol (or 3+ dipstick)
2. Hypoalbuminaemia — <25 g/L
3. Oedema (periorbital first → scrotal/labial → ascites/pleural) — from low oncotic pressure
4. Hyperlipidaemia (cholesterol ↑)

Aetiology by age:

Pathology: MCD — normal light microscopy, effacement of foot processes on EM, negative immunofluorescence → steroid-responsive.

Clinical: periorbital oedema (worse in morning), puffy face, weight gain, oliguria, frothy urine; BP usually normal (unlike nephritic); urine dipstick 3-4+ protein.

Complications (important):

Management:

1. Confirm diagnosis — urine protein, serum albumin, lipids; USS kidneys; (biopsy only if atypical — age <1 or >10, macroscopic haematuria, low C3, steroid-resistant).
2. Prednisolone (steroid) induction: 60 mg/m²/day × 4 weeks then 40 mg/m² alternate days × 4 weeks (or per protocol).
3. Response: ~90% remit within 4 weeks (steroid-sensitive NS — SSNS).
4. Relapses (common): repeat steroid course; frequent relapses/steroid-dependent → second-line: levamisole, cyclophosphamide, calcineurin inhibitors (tacrolimus/cyclosporin), rituximab; steroid-resistant → biopsy + specialist (FSGS, MPGN).
5. Supportive: salt/fluid restriction during oedema, albumin + furosemide for severe hypovolaemia/oedema, penicillin prophylaxis + pneumococcal vaccine (infection risk), daily urine dipstick at home, school attendance normal, avoid live vaccines on high-dose steroids.

Prognosis: SSNS — excellent, most outgrow by puberty; steroid-resistant — worse (FSGS → CKD risk).

2. Acute post-streptococcal glomerulonephritis (APSGN)

Pathogenesis: immune complex (IgG + C3) deposition after group A streptococcal infection (pharyngitis 1-2 weeks or skin 2-6 weeks earlier) → glomerular inflammation (increased cellularity, IgG+C3 deposits, subepithelial humps on EM).

Clinical (1-2 weeks after sore throat / 2-6 weeks after skin infection):

• Haematuria — macroscopic "cola-coloured/tea-coloured urine" (classic)
• Oedema (facial/periorbital, morning)
• Hypertension (salt/water retention) — headache, seizures if severe
• Oliguria (variable)
• Mild proteinuria

Investigations:

Differential: IgA nephropathy (haematuria during/resolved URTI, normal C3), MPGN (persistent low C3), lupus nephritis, HSP nephritis.

Management (SUPPORTIVE — no specific treatment):

1. BP control — nifedipine/amlodipine; fluid + salt restriction; diuretics (furosemide) if fluid overload/oedema.
2. Monitor — BP, urine output, renal function, electrolytes.
3. Antibiotics — treat underlying strep infection (penicillin if active infection present; does NOT change nephritis course).
4. Dialysis if severe oliguric AKI/hyperkalaemia/pulmonary oedema.

Prognosis: excellent in children — >95% full recovery; C3 normalises by 6-8 weeks; low risk of chronic kidney disease (persistent proteinuria/haematuria >6 months → refer; persistent ↓C3 >8 weeks → MPGN/lupus).

3. Urinary tract infection (UTI)

Definition: bacterial infection of the urinary tract — cystitis (lower) vs pyelonephritis (upper — fever, loin pain).

Why important in children: renal scarring from recurrent/pyelonephritic UTI → hypertension, CKD; VUR (vesicoureteral reflux) is the main risk factor; UTI in infants often presents without localising signs (fever only).

Risk factors: VUR, female sex, age <1, urinary obstruction (posterior urethral valves in boys), constipation, poor hygiene, catheterisation, voiding dysfunction.

Clinical:

Diagnosis:

• Urinalysis: pyuria (leukocyte esterase+), nitrite+ (gram-negative) — screening.
• Urine culture (midstream / catheter / suprapubic in infants) — the diagnostic test: >10⁵ CFU/mL (clean catch) or >10⁴ (catheter) significant.
• Sepsis screen in young/ill infants (blood culture, LP if febrile young infant).

Management:

1. Antibiotics — empiric then per culture: amoxicillin-clavulanate, third-generation cephalosporin (cefixime/ceftriaxone), TMP-SMX (older); pyelonephritis/young infant → IV antibiotics (ceftriaxone) + admit.
2. Rehydration, antipyretics.
3. Urgent USS — hydronephrosis/abscess/obstruction (within 24-48 h if pyelonephritis).
4. Further imaging after first febrile UTI (young children): USS + DMSA scan (scarring) ± MCUG (VUR — after 2nd infection or abnormal USS).
5. Prophylaxis: low-dose antibiotics (trimethoprim) for VUR/grade ≥3 reflux or recurrent UTI; circumcision may reduce UTI in boys with VUR; treat constipation/voiding dysfunction.

Posterior urethral valves (PUV — boys): antenatal hydronephrosis, poor stream, distended bladder — obstruction → urgent surgery (valve ablation); long-term CKD risk — think in any boy with UTI + poor stream.

High-Yield Points

Topic Summary

Nephrotic syndrome = proteinuria + hypoalbuminaemia + oedema + hyperlipidaemia; minimal change → steroid-responsive (>90%); watch for infection (pneumococcal), thrombosis, and steroid toxicity; relapses treated with repeated steroids or steroid-sparing agents. APSGN = post-strep immune complex disease — cola urine + hypertension + ↓C3 + ↑ASO, treated supportively with excellent prognosis (C3 back by 6-8 weeks). UTI — especially in infants (fever only) — needs urinalysis + culture, prompt antibiotics, and imaging (USS/DMSA/MCUG) because VUR + scarring → hypertension/CKD.