Thrombotic microangiopathies and the kidney

Thrombotic microangiopathies are rare and carry a high morbidity and mortality. Recent research has helped to clarify their aetiology. A high index of suspicion is required in patients presenting with renal impairment and features of microangiopathy such as a low platelet count and Coomb's test-negative haemolytic anaemia. In Shiga toxin-mediated haemolytic—uraemic syndrome (HUS), bacteria such as Escherichia coli O157 adhere to the intestinal mucosa, and secrete a highly potent Shiga cytotoxin, which binds to the glomerular endothelium and causes an endotheliopathy. In atypical HUS, the alternative pathway of complement, in the absence of an intact regulatory system, runs out of control. The endothelium is the predominant target, in a variety of organs including the kidneys, brain and heart. In thrombotic thrombocytopenic purpura, dysfunction of an enzyme (ADAMTS13) that cleaves and inactivates ultra-large multimers of von Willebrand factor leads to the formation of platelet-rich thrombi. Most thrombotic microangiopathies are treatable if identified early.