Thrombotic thrombocytopenic purpura and hemolytic uremic syndrome

Thrombotic thrombocytopenic purpura is an uncommon disease with an untreated mortality approaching 100 per cent. It is characterized clinically by fever, thrombocytopenic purpura, microangiopathic hemolytic anemia, and ischemically mediated neurological and renal impairment. These findings are variably identified at initial presentation, but the presence of all five signs implies more severe disease and generally portends a worse prognosis. A large multicenter Canadian randomized unblinded trial involving 102 patients demonstrated that plasmapheresis was superior to plasma infusion alone. At 6 months, 15 per cent more patients survived in the plasmapheresis group (p = 0.036) with a survival rate of 78 per cent. However, patients with severe renal failure were excluded from the study, less than 65 per cent had neurological findings, and less than 25 per cent had fever at the time of presentation.

No trials have been performed for hemolytic uremic syndrome which shares common pathophysiological features with thrombotic thrombocytopenic purpura. Patients presenting with thrombocytopenic purpura, microangiopathic hemolytic anemia, and neurological signs, fever, and oliguria severe enough to preclude randomization in the Canadian study represented 18 per cent of the total number of patients presenting with thrombotic thrombocytopenic purpura-hemolytic uremic syndrome. They had a survival rate similar to those patients treated with plasmapheresis in the randomized study, suggesting that patients with the most severe form of the disease also benefit. An elevated von Willebrand factor antigen level was found in all patients in whom it was measured; some evidence suggests that cryosupernatant plasma (plasma devoid of cryoprecipitate and thus large multimers of von Willebrand factor) may be more beneficial than fresh frozen plasma in the treatment of thrombotic thrombocytopenic purpura.

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