Define Acute Post-Streptococcal Glomerulonephritis. Describe its aetiology, clinical features, investigations and management.

Definition

• Acute post-streptococcal glomerulonephritis (APSGN) is an immune-complex-mediated glomerular inflammation occurring after infection with nephritogenic strains of Group A streptococcus.
• It is the commonest cause of acute nephritic syndrome in children.

Etiology & Pathogenesis

• Follows a streptococcal throat infection (after 1–2 weeks) or a skin infection/pyoderma (after 3–6 weeks).
• Immune complexes (streptococcal antigen + antibody) deposit in the glomeruli → complement activation and inflammation.
• This causes a proliferative glomerulonephritis with reduced glomerular filtration and salt/water retention.

Clinical Features (acute Nephritic Syndrome)

• Haematuria — 'smoky', cola- or tea-coloured urine (the hallmark).
• Oedema — typically periorbital and facial, worse in the morning.
• Hypertension — from salt and water retention (may be significant).
• Oliguria and mild–moderate proteinuria.
• A preceding sore throat or skin infection in the history.

Investigations

• Urinalysis — haematuria with dysmorphic RBCs and RBC casts (glomerular origin), and proteinuria.
• Evidence of streptococcal infection — raised ASO titre (throat) or anti-DNase B (skin); throat/skin swab.
• Low C3 complement — a key finding that returns to normal within 6–8 weeks.
• Raised blood urea and creatinine; electrolytes.

Management

• Mainly supportive — salt and fluid restriction, and diuretics (furosemide) for oedema/hypertension.
• Antihypertensives (calcium-channel blockers/others) for significant hypertension.
• Penicillin to eradicate any residual streptococcal infection.
• Manage complications and monitor renal function, BP and urine output; rest during the acute phase.

Complications

• Hypertensive encephalopathy (headache, vomiting, seizures) — a hypertensive emergency.
• Acute pulmonary oedema / heart failure from fluid overload.
• Acute kidney injury (usually transient); electrolyte disturbances.

Prognosis

• The prognosis in children is excellent — APSGN is usually self-limiting.
• Urine output improves within days, C3 normalises by 6–8 weeks, and microscopic haematuria may persist for up to a year.
• Progression to chronic kidney disease is rare in children (unlike adults).

Epidemiology

• Commonest in children aged 5–12 years; more common where streptococcal skin infection is prevalent.
• Follows only certain 'nephritogenic' streptococcal strains.

Differential Diagnosis of Acute Nephritis

• IgA nephropathy (haematuria with the infection, normal C3), Henoch-Schönlein purpura nephritis (with rash).
• Lupus nephritis and membranoproliferative GN (persistently low C3) — considered if C3 stays low beyond 8 weeks.

Management of Hypertensive Emergency

• For hypertensive encephalopathy — controlled BP reduction with agents such as labetalol or nifedipine, plus a diuretic.
• Avoid abrupt, excessive falls in blood pressure; treat seizures.

Management of Fluid Overload

Salt and fluid restriction with furosemide usually controls the circulatory congestion; occasionally, severe fluid overload with pulmonary oedema or refractory hyperkalaemia/uraemia needs short-term dialysis.

Pathology

The kidneys show a diffuse proliferative glomerulonephritis; immunofluorescence reveals granular deposits of IgG and C3 ('starry-sky' pattern), and electron microscopy shows subepithelial 'humps'.

Natural History

• Urine output and oedema improve within 1–2 weeks; blood pressure normalises early.
• Microscopic haematuria may persist for 6–12 months; C3 normalises by 6–8 weeks.

Prevention

Prompt treatment of streptococcal throat and skin infections and good skin hygiene reduce the incidence; there is no role for long-term penicillin prophylaxis after a single episode.

Indications for Renal Biopsy (atypical Cases)

• Persistently low C3 beyond 8 weeks; heavy (nephrotic-range) proteinuria.
• Progressive renal failure or rapidly deteriorating function; anuria.
• Recurrence or an atypical course suggesting another glomerulonephritis.