[Plasma exchange failures in two patients with thrombotic thrombocytopenic purpura]

We treated two patients with thrombotic thrombocytopenic purpura (TTP) with multiple plasma exchanges for a short period. Following 6 plasma exchanges during 11 days in patient 1 and the 8 exchanges during 13 days in patient 2, consciousness disturbance and thrombocytopenia improved with a decrease in serum lactate dehydrogenase (LDH) levels in both patients. However, thrombocytopenia rapidly progressed with a rise of serum LDH levels after a few days from cessation of the treatment. They received a few rounds of plasma exchange without beneficial effects and eventually died of massive hemorrhage. The clinical course of these patients indicates that some patients with TTP are refractory to repeated plasma exchanges for a short period. It seems important to determine the target point in blood chemistry values such as the LDH level for plasma exchange at which the treatment could be discontinued without causing relapse of TTP.