Thrombotic Thrombocytopenic Purpura
By Dr Rob Hackett
TTP consists of the pentad of:
- Microangiopathic haemolytic anaemia
- Thrombocytopenic purpura
- Neurologic abnormalities
- Fever
- 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
Laboratory Investigations:
- Measuring ADAMTS13 activity level may aid in diagnosis.
- FBC – ? Hb + Platelets
- Bilirubin + LDH
- Blood film
- Coagulation screen
- U+E
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.