Thrombotic thrombocytopenic purpura (congenital and acquired) and haemolytic-uraemic syndrome

Thrombocytopenia and haemolytic anaemia are the hallmarks of thrombotic microangiopathies, thrombotic thrombocytopenic purpura (TTP) and haemolytic uremic syndrome (HUS). TTP, inherited or immunomediated, is caused by the plasma deficiency of the von Willebrand factor cleaving protease ADAMTS13 owing to gene mutations or autoantibodies. Typical HUS is more often caused by infections with Shiga-toxin-producing Escherichia coli . The rarer atypical forms are mainly associated with the dysregulation of complement proteins. An accurate differential diagnosis is warranted because plasma exchange (the treatment of choice in TTP) is much less effective in atypical HUS, which shows dramatic therapeutic benefits from the use of eculizumab, a monoclonal antibody that inhibits complement activation. The measurement of ADAMTS13 is able to diagnose accurately TTP and very simple tests such as the platelet count and serum creatinine can predict protease deficiency with a good degree of accuracy. On the other hand, specific clinical or laboratory tests for diagnosing atypical HUS are still lacking.