HUS

Haemolytic Uraemic Syndrome (HUS)

Haemolytic Uraemic Syndrome (HUS) is a rare but life-threatening condition in children. It’s characterised by a triad of microangiopathic haemolytic anaemia, thrombocytopenia, and acute kidney injury. The most common form in the UK is linked to Shiga toxin-producing E. coli (STEC), making it a key differential in a child presenting with bloody diarrhoea.

 

Pathophysiology

HUS is caused by toxins that damage the endothelial lining of the small blood vessels. This damage leads to the formation of microthrombi (tiny blood clots), which cause three main problems:

  • Microangiopathic haemolytic anaemia: As red blood cells try to pass through the damaged and narrowed vessels, they are sheared and destroyed, leading to haemolytic anaemia.

  • Thrombocytopenia: Platelets are consumed in the formation of microthrombi, leading to a low platelet count.

  • Acute kidney injury: The microthrombi block the small blood vessels in the kidneys, leading to ischaemic damage and a sudden reduction in kidney function.

 

Aetiology

  • Typical (D+) HUS: This is the most common form, accounting for 90% of cases in the UK. It is caused by Shiga toxin-producing E. coli (STEC), particularly the O157 strain. The toxin is produced after an E. coli infection, usually from contaminated food or water.

  • Atypical (D-) HUS: This is a rarer form not associated with diarrhoea. It is often caused by a genetic mutation in the complement pathway, which leads to uncontrolled activation of the complement system.

 

Clinical Presentation

  • Prodrome: The illness typically starts with a prodrome of bloody diarrhoea and abdominal pain, which lasts for several days.

  • Classic Triad: After the prodromal phase, the classic triad of HUS develops:

    • Haemolytic Anaemia: Presents with pallor and jaundice.

    • Thrombocytopenia: Leads to petechiae and bruising.

    • Acute Kidney Injury: Presents with oliguria or anuria (reduced or no urine output).

  • Systemic Manifestations: In severe cases, HUS can affect other organs, leading to neurological complications (seizures, altered consciousness) or pancreatitis.

 

Investigations

  • Bloods:

    • Full Blood Count: Shows anaemia and thrombocytopenia.

    • U&Es: Elevated urea and creatinine, indicating acute kidney injury.

    • Lactate Dehydrogenase (LDH): Very high LDH is a key sign of haemolysis.

  • Microbiology: Stool culture is essential to identify the STEC strain.

  • Other: A urinalysis will show protein and blood in the urine.

 

Management

Management is primarily supportive and is best conducted in a paediatric intensive care unit (PICU).

  • Fluid and Electrolyte Management: Careful monitoring and management of fluid balance are essential to prevent fluid overload.

  • Renal Support: Many children require dialysis to manage acute kidney injury.

  • Blood Transfusions: Red blood cell transfusions may be needed to manage severe anaemia.

  • Atypical HUS: Atypical HUS is treated with a specific monoclonal antibody, eculizumab, that blocks the complement system.

 

Prognosis

The prognosis for typical HUS is generally good, with most children making a full recovery. However, some may be left with residual kidney damage, and long-term follow-up with a paediatric nephrologist is essential.