Natural history of thrombotic thrombocytopenic purpura and hemolytic uremic syndrome.

The differential diagnosis of thrombotic microangiopathy (TMA) has become clearer following the establishment of the relationships between (1) diarrhea-associated hemolytic uremic syndrome (HUS) and Shiga toxin-producing Escherichia coli-HUS (STEC-HUS), (2) a markedly reduced ADAMTS-13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) level and typical thrombotic thrombocytopenic purpura (TTP), and (3) abnormalities in the complement regulatory system and atypical HUS (aHUS). These TMAs include typical TTP, other forms of TMA, STEC-HUS, and aHUS. The pathological mechanisms of TMA still overlap among several forms of TMA. With respect to the management of TMA, the use of plasma exchange (PE) for typical TTP, additional steroid therapy for TMA and rituximab for typical TTP with a high titer of the inhibitor of ADAMTS-13, as well as eculizumab for aHUS, have also been established. Although several issues remain in the pathophysiology and management of TMA, new findings will hopefully resolve these problems in the near future.