Three patients with thrombotic thrombocytopenic purpura (TTP) were treated by infusion of normal plasma with dramatic responses. The plasmas collected from these patients during relapse induced in vitro aggregation of washed platelets from both normal donors and the patients during remission. The platelet aggregating factor was not dialyzable or adsorbable by Al(OH)3 and was not inactivated by diisopropylfluorophosphate, hirudin, or heparin in the presence of normal amounts of antithrombin. In contrast to the platelet aggregation induced by platelet isoantibody, the platelet aggregating activity of TTP plasma diminished as a function of time when it was incubated with normal plasma at 37 degrees C. These observations suggest that at least some instances of TTP appear to be due to deficiency of a plasma inhibitor to counteract a platelet aggregating factor demonstrated to be present in the plasma of these patients.

A patient with thrombotic thrombocytopenic purpura (TTP) showed for the first time catastrophic signs and symptoms of CNS involvement immediately after infusion of platelets. Postmortem examination revealed extensive deposits of platelet aggregates within the small blood vessels of the brain, whereas lesions elsewhere in the body consisted of platelets as well as fibrin and were associated with endothelial proliferation and microaneurysm formation. These findings are consistent with the view that the initial event in TTP may be platelet aggregation. The plasma of this patient contained platelet-aggregating activity. We conclude that platelet transfusions in patients with TTP may aggravate the disease process.

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