Thrombotic Thrombocytopenic Purpura
By Dr Rob Hackett
TTP consists of the pentad of:
- Microangiopathic haemolytic anaemia
- Thrombocytopenic purpura
- Neurologic abnormalities
- Renal disease
Untreated mortality = 90%
Treatment with plasma exchange = 10-20%
Lack of plasma protease – A Disintegrinlike And Metalloprotease with ThromboSpondin type 1 motif 13 (ADAMTS13) – responsible for the breakdown of ultralarge vWF multimers.
Platelet-vWF complexes form small blood clots which circulate in the blood vessels and cause shearing of red blood cells, resulting in their rupture – Haemolytic anaemia and Schistocyte formation.
Similar to HUS but differentiated by coagulation screen results.
In TTP, the organ most obviously affected is the brain; in HUS, the kidney.
Relapses are not uncommon, occurring in 13-36% of patients.
Severe bleeding from thrombocytopenia is unusual, although petechiae are common
- Measuring ADAMTS13 activity level may aid in diagnosis.
- FBC – ? Hb + Platelets
- Bilirubin + LDH
- Blood film
- Coagulation screen
Tx of choice for TTP is plasma exchange with fresh frozen plasma
Transfusion is contraindicated in thrombotic TTP, as it fuels the coagulopathy.
Corticosteroids may be used in refractory patients
Rituximab, a monoclonal antibody aimed at the CD20 molecule on B lymphocytes – destruction of B cells reduces the production of the protease inhibitor.