We appreciate the letter by Drs. Stein and Flexner, who have observed and reported cases similar to ours [1]. As emphasized by Dr. Stricker, the association of ITP and TTP may not be rare and may instead be underdiagnosed.

In response to Dr. Zucker-Franklin, we stand by our diagnosis. The classic pentad for TTP is present in only few cases. Of the patients reviewed by Ridolfi and Bell [2], 74% had only microangiopathic hemolytic anemia, thrombocytopenia, and neurologic symptoms [3]. Our patient had personality changes (which were admittedly difficult to distinguish from postpartum depression) and was receiving steroids, which may have suppressed her fever, as we addressed in our original report. Although Zucker-Franklin and Karpatkin [4] have reported erythrocyte and platelet fragmentation in patients with ITP, as noted by electron microscopy, they and others have not described a fulminant schistocytosis that is visible on routine peripheral blood smear and is accompanied by marked lactate dehydrogenase elevation, as occurred in our patient and which would be most unusual for ITP. Although the Evan syndrome is a possible diagnosis for any patient with ITP and acquired hemolytic anemia, it is defined in part by the presence of autoantibodies directed at erythrocytes [5]. Our patient did not have microspherocytes and did not have anti-erythrocyte antibodies. (Both direct and indirect test results were negative.)

We agree that a skin or mucosal skin biopsy might have been useful to support the diagnosis of TTP but did not believe it necessary in this case. Instead, the sudden onset of a Coomb-negative, microangiopathic, hemolytic anemia and thrombocytopenia in the postpartum period, without hypertension or significant proteinuria, suggested TTP. In addition, our patient's dramatic response to plasmapheresis, with complete normalization of her smear results and lactate dehydrogenase level, further supports the diagnosis.