Atypical hemolytic uremic syndrome: from diagnosis to treatment.

Thrombotic microangiopathy (TMA) is a relatively rare condition but a medical urgency requiring immediate intervention to avoid irreversible organ damage or death. Symptoms on presentation include microangiopathic haemolytic anaemia, thrombocytopenia and organ damage. The most frequent direct causes of TMA are thrombotic thrombocytopenic purpura (TTP) and haemolytic uremic syndrome (HUS). The most common form of HUS is related to Shiga toxin producing Escherichia coli (STEC) infection while approximately 10% of cases are due to dysregulation of the complement pathway (atypical haemolytic uremic syndrome, aHUS). Optimal treatment regimens differ depending on the underlying cause; however, differential diagnosis may be difficult. The most accurate method of diagnosis is based on exclusion and should consider, beyond the symptoms common to TMA, ADAMTS13 activity levels and STEC infection status. For the management of TTP, plasma exchange (PE) is the most important acute intervention and is associated with lower mortality and better outcomes than plasma infusion. In most patients with STEC-HUS, the course of disease is self-limiting although management of acute kidney injury is often required. Until recently, the management of aHUS consisted of early and intensive PE, although this was mostly ineffective in protecting from subsequent organ damage. Eculizumab, an inhibitor of the alternative complement pathway, produces a rapid and sustained inhibition of the TMA process, with significant improvements in long-term clinical outcomes. Due to the significant improvement achieved, eculizumab has subsequently been approved as first-line therapy when an unequivocal diagnosis of aHUS has been made.