Thrombotic thrombocytopenic purpura. Haemolytic uraemic syndrome
1. Big picture
Thrombotic thrombocytopenic purpura (TTP) and haemolytic uraemic syndrome (HUS) belong to the group of thrombotic microangiopathies (TMA).
The shared core is:
Platelet-rich microthrombi in small vessels
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Red cells are mechanically fragmented
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Microangiopathic haemolytic anaemia + thrombocytopenia + organ injury
The examiner wants you to recognize this pattern:
Low platelets + Coombs-negative haemolysis + schistocytes + normal PT/aPTT = TTP/HUS until proven otherwise.
TTP and HUS are both thrombotic emergencies, but they differ in mechanism and dominant organ involvement. TTP is mainly due to severe ADAMTS13 deficiency, while HUS is mainly renal and is either Shiga toxin-associated or complement-mediated atypical HUS.
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