haemolytic uraemic syndrome

Question 1

definition

Answer 1

Haemolytic uraemic syndrome (HUS) is characterised by microangiopathic haemolytic anaemia, thrombocytopenia, and acute kidney injury. Ninety percent of HUS cases occur in the paediatric population, due to Shiga toxin-producing Escherichia coli(STEC), and are diarrhoea-associated (D+ HUS).

Rarely other organisms, such as Shigella and Streptococcus pneumoniae, are implicated.

Acute kidney injury necessitating dialysis develops in approximately half of children with diarrhoea-associated HUS.

Adequate hydration is important to minimise renal damage in HUS associated with Shiga toxin-producing E coli infections. Avoidance of antibiotics, antimotility agents, and non-steroidal anti-inflammatory drugs is advised. Cautious use of opioids is advised; there are insufficient data on the effect of opioids on the course of HUS.

Anaemia can be treated with red cell transfusion. Platelet transfusions are generally avoided in the absence of active bleeding.

Atypical HUS occurs due to abnormalities in the alternative complement regulatory pathway, resulting in endothelial cell damage and causing microvascular thrombosis. Atypical HUS can occur in adults, and in some children.

Atypical HUS can occur due to genetic or acquired abnormalities in the alternative complement regulatory pathway. HUS can also occur as a secondary phenomenon due to medications, cancer, and other systemic diseases.

Question 2

symptoms

Answer 2

• GI: Severe abdominal colic, watery diarrhoea that becomes bloodstained.
• General: Malaise, fatigue, nausea, fever <38 degrees
• Renal: Oliguria or anuria, haematuria.

Question 3

signs

Answer 3

• General: Pallor (from anaemia), slight jaundice (from haemolysis), bruising (severe thrombocytopaenia), generalized oedema, hypertension and retinopathy.
• GI: Abdominal tenderness.

Question 4

risk factors

Answer 4

ingestion of contaminated food/water, known community outbreak of toxigenic E coli, egenetic predispostion (in atypical HUS)

Question 5

investigations

Answer 5

1st investigations:

• FBC
• peripheral blood smear
• renal function/creatinine
• serum electrolytes (because of diarrhoea/AKI)
• PT, PTT => normal (as opposed to increased in other causes of thrombocytopenia, such as disseminated intravascular coagulation)
• LDH => increased (released by RBC lysis)
• haptoglobin => decreased (binds to free haemoglobin from RBC lysis)
• stool culture -> PCR for shiga 1/2 + test for Ecoli bacteria
• complement H and I levels (abnormal in atypical and some familial HUS)

others:

• urinalysis (for renal function, although not very accurate when having diarrhoea)
• ADAMTS13 level (to check for TTP cause, lower in TTP than HUS)
• LFTs (check liver involvement)
• serum amylase, lipase, glucose (monitor kidney function, check pancreas involvement)