Question
A 7-year-old boy presents with puffiness of eyelids, decreased urine output of 6 days duration. Clinical examination reveals generalized edema and mild hypertension. Urine examination reveals numerous RBCs and mild proteinuria. He gives a history of a sore throat 3 weeks ago. A renal biopsy is performed. (
- (a) What is your provisional diagnosis ( 2 mark(s)
- (b) Describe the pathogenesis of this condition ( 5 mark(s)
- (c) What features do you expect to see in the renal biopsy ( 6 mark(s)
- (d) What is the outcome of this disease 2 mark(s)
Answer
(a) Provisional diagnosis: Acute Post-Streptococcal Glomerulonephritis (PSGN) — the clinical picture of periorbital puffiness, oliguria, generalized edema, mild hypertension, and haematuria with mild proteinuria, occurring 2–3 weeks after a streptococcal sore throat, is classic for acute PSGN.
(b) Pathogenesis: PSGN follows infection with nephritogenic strains of Group A beta-haemolytic Streptococcus (typically types 12, 4, and 1). It is an immune-complex mediated (Type III hypersensitivity) glomerulonephritis:
- Streptococcal antigens (e.g., streptococcal exotoxin B/SPE B, or a “nephritis strain-associated protein,” NSAP) are planted in the glomerular basement membrane (GBM), or circulating immune complexes formed with these antigens are deposited in the glomeruli.
- This occurs after a latent period (1–4 weeks) that allows the host to mount an antibody response — hence PSGN is a delayed, not direct infective, process.
- Deposited antigen-antibody complexes activate the complement cascade (causing transient hypocomplementemia, low C3), attracting neutrophils and monocytes.
- Inflammatory mediators and complement-derived chemotactic factors cause endothelial and mesangial cell proliferation and neutrophilic infiltration, producing a diffuse proliferative glomerulonephritis.
- This inflammation reduces the glomerular filtration surface and increases capillary permeability, producing oliguria, azotaemia, hypertension (from salt/water retention), and haematuria (RBCs leaking through damaged capillary walls).
(c) Renal biopsy findings:
- Light microscopy: Diffuse proliferative glomerulonephritis — enlarged, hypercellular glomeruli due to proliferation of endothelial and mesangial cells, with heavy infiltration by neutrophils and monocytes (“exudative” pattern).
- Immunofluorescence: Granular (“lumpy-bumpy”) deposits of IgG and C3 along the GBM and in the mesangium.
- Electron microscopy: Discrete, dome-shaped subepithelial deposits called “humps.”
(d) Outcome: The prognosis in children is excellent — over 95% recover completely with conservative/supportive management (rest, salt restriction, diuretics for oedema and hypertension). A small minority (especially adults) may show persistent proteinuria/haematuria, and rarely progress to rapidly progressive glomerulonephritis (RPGN) or, in a very small percentage, chronic glomerulonephritis with progression to chronic kidney disease.