Haemolytic uraemic syndrome

Haemolytic uraemic syndrome (HUS) is a thrombotic microangiopathy characterised by thrombocytopaenia, microangiopathic haemolysis, and renal abnormalities. Levels of ADAMTS-13 is normal, unlike in TTP.

HUS predominantly affects children <5 and is caused by bacterial toxins. The condition might result in acute kidney injury and must be treated immediately. It’s more common than TTP.

Etiology

Over 90 % of cases occur due to infection by Shiga-like toxin produced by bacteria like EHEC. It is especially associated with the serotype O157:H7. Approximately 10 % of children with EHEC infection develop HUS.

The remaining cases are caused by gene mutations or pneumococcal infection.

Classification

Primary HUS – previously called atypical HUS (aHUS)
- Those cases caused by genetic mutations
Secondary HUS – previously called typical HUS (90% of cases)
- Those cases caused by infections
- Shiga toxin HUS
  - EHEC – O157:H7
  - Shigella dysenteriae
- Pneumococcal HU

Clinical features

Shiga toxin HUS is usually preceded by bloody diarrhoea in the past 5 – 10 days. HUS presents with the following three clinical features, all of which are also features of TTP:

Thrombocytopaenia
- Petechiae
- Purpura
Microangiopathic haemolytic anaemia
Impaired renal function
- Oliguria

Renal symptoms are more severe in HUS than in TTP.

Diagnosis

Laboratory
- Thrombocytopaenia
- Haemolytic anaemia
- Increased urea/BUN and creatinine
Negative Coombs test
Peripheral blood smear
- Schistocytes – fragmented RBCs

Stool culture for EHEC or Shigella in case of secondary HUS.

Treatment

Supportive treatment is usually enough, but 50% of the patients might require dialysis due to the development of AKI. Plasma exchange is given in refractory cases. Immediate treatment is needed to prevent permanent kidney injury.

In case of primary (atypical HUS) Eculizumab is very effective.

Avoid antibiotics and antimotility agents when treating Shigella or EHEC as they can increase the risk for the development of HUS.