Thrombotic Thrombocytopenic Purpura

Thrombotic Thrombocytopenic Purpura (TTP) is a haematological emergency. There are broadly two forms - both rare. The congenital form of TTP is due to a deficiency in the enzyme ADAMTS13. It is extremely rare, generally has a family history, and patients can be managed with plasma infusion or recombinant protein administration. These patients will rarely cross the front door. The more acute and more likely are the acquired TTPs. These can be primary - i.e. there is an antibody directly to ADAMTS13 which reduces the level, or secondary - where there is another cause reducing the active level of the protein, or another condition which is causing the antibody resulting in the clearance.

TTP presents as a pentad of fever, neurological compromise, renal failure, thrombocytopenia and anaemia. The diagnosis should be highly suspected whenever there are red cell fragments easily visible on the blood film. An arbitrary cut off of 10 fragments per high powered field has been suggested, but in reality if the clinical syndrome fits TTP and the number is less than this you would check. You would also see thrombocytopenia, and signs of haemolysis such as reticulocytosis and spherocytosis. 

Treatment is with steroids, plasma exchange, B cell reduction and inhibition of complement mediated lysis.  Treatment needs to be intiated immediately - so historically one would always transfer a patient with TTP to the treating centre as ADAMTS13 asays and anti-ADAMTS13 antibody assays took several days. Now this turnaround time is a few hours or less in most laboratories, all cases should be discussed with your referring centre. They may want a sample, the film or the patient depending on the history.