[Hemolytic uremic syndrome in adults]

Hemolytic uremic syndrome (HUS) is related to a renal thrombotic microangiopathy, inducing hypertension and acute renal failure (ARF). Its pathogenesis involves an activation/lesion of microvascular endothelial cells, mainly in the renal vasculature, secondary to bacterial toxins, drugs, or autoantibodies. An overactivation of the complement alternate pathway secondary to a heterozygote deficiency of regulatory proteins (factor H, factor I or MCP) or to an activating mutation of factor B or C3 can also result in HUS. Less frequently, renal microthrombi are due to an acquired or a constitutional deficiency in ADAMTS-13, the protease cleaving von Wilebrand factor. Hemolytic anemia with schistocytes, thrombocytopenia without evidence of disseminated intravascular coagulation, and renal failure are consistently found. In typical HUS, a prodromal diarrhea, with blood in the stools, is observed, related to pathogenic enterobacteria, most frequently E. Coli O157:H7. HUS may also occur in the post partum period, and is then related to a factor H or factor I deficiency. HUS may also occur after various treatments such as mitomycin C, gemcitabine, ciclosporin A, or tacrolimus, and as reported more recently bevacizumab, an anti VEGF antibody. Atypical HUS are not associated with diarrhea, may be sporadic or familial, and can be related to an overactivation of the complement alternate pathway. More recently, some of them have been related to a mutation of thrombomodulin, which also regulates the alternate pathway of complement. In adults, several HUS are encountered in the course of chronic nephropathies: nephroangiosclerosis, chronic glomerulonephritis, post irradiation nephropathy, scleroderma, disseminated lupus erythematosus, antiphospholipid syndrome. Overall the prognosis of HUS has improved, with a patient survival greater than 85% at 1 year. Chronic renal failure is observed as a sequella in 20 to 65% of the cases. Plasma infusions and plasma exchanges are effective in most of the cases to treat hemolysis and thrombocytopenia. Steroid therapy is debated, as well as immunosuppressive drugs, including rituximab, in autoimmune forms. A new monoclonal anti-C5 antibody is tested, and seems to be effective in atypical HUS with abnormal complement alternate pathway activation. If terminal renal failure occurs, renal transplantation can be performed but the risk of recurrence, which very low in post infectious forms of HUS, is about 70 to 80% in genetic forms of complement regulatory protein deficiency.