Define Haemolytic Uraemic Syndrome. Describe its aetiology, pathogenesis, clinical features and investigations.

Definition

• Haemolytic uraemic syndrome (HUS) is a thrombotic microangiopathy defined by a triad of: microangiopathic haemolytic anaemia, thrombocytopenia, and acute kidney injury.
• It is a leading cause of AKI in young children.

Types & Etiology

• Typical (D+, diarrhoea-associated) HUS — the commonest; follows Shiga-toxin-producing infection (E. Coli O157:H7, Shigella dysenteriae type 1).
• Atypical HUS — complement dysregulation (no diarrhoeal prodrome; often familial/recurrent).

Pathogenesis

Shiga toxin damages vascular endothelium → platelet-fibrin microthrombi in small vessels → mechanical destruction of red cells (schistocytes), consumption of platelets, and renal ischaemia.

Clinical Features

• Typically 5–10 days after an episode of bloody diarrhoea.
• Pallor, lethargy, reduced urine output (oliguria/anuria), oedema and hypertension.
• Bleeding/petechiae (thrombocytopenia); may have CNS involvement (seizures).

Investigations & Management

• Blood — anaemia with schistocytes on film, thrombocytopenia, raised urea/creatinine, raised LDH.
• Mainly supportive — fluid & electrolyte management, control of hypertension, blood transfusion, and dialysis for AKI.
• Avoid antibiotics and anti-motility drugs in Shiga-toxin (typical) HUS; eculizumab for atypical HUS.

Complications

• Severe AKI needing dialysis; hypertension; fluid and electrolyte disturbances.
• CNS involvement (seizures, altered sensorium); rarely colitis complications.

Prognosis

• Typical (diarrhoea-associated) HUS usually recovers with supportive care and has a good prognosis, though some children are left with residual hypertension, proteinuria or reduced kidney function and need follow-up.
• Atypical HUS is more likely to relapse and progress.