Elevated platelet-surface-bound IgM in thrombotic thrombocytopenic purpura.

The level of platelet-surface-bound IgM (PSIgM) was measured during the course of therapy in two patients with thrombotic thrombocytopenic purpura (TTP). Before therapy, both had significantly elevated PSIgM. In both cases the PSIgM dropped after the institution of treatment with plasmapheresis, steroids, and dipyridamole, correlating with a complete response to therapy in one patient and a partial response in the second. This is further evidence that in some cases of TTP, an immune mechanism is present.