Four of the 27 patients who relapsed were treated in hospitals outside the Registry region, and data are not sufficient to calculate outcomes other than survival; all 4 survived. Ten of the initial episodes and 14 of the relapses occurred in December 2003 through December 2015; rituximab was used for some patients during this time.

The total number of patients with severe neurologic abnormalities was not different between the 2 groups (P = .234).

Laboratory data, treatment, and the outcomes of response and exacerbation are described for 22 patients, omitting the patient who died suddenly before TTP was diagnosed at autopsy. For LDH values, only 21 patients were compared because 1 patient did not have LDH measured during her relapse episode. The platelet counts (P = .017) and hematocrits (P = .003) were significantly higher in these patients at the time of relapse; the LDH levels were significantly lower (P < .001). There was no different between the creatinine levels (P = .130).

The number of PEX treatments (P = .005) and days in hospital (P = .003) were significantly less for relapse episodes.

A 51-year-old man who was deaf from birth and could not speak had an acute myocardial infarction with hypotension requiring intra-aortic balloon pump circulatory assistance in 2004, 4 years after his initial TTP episode. His hematocrit was 25%, platelet count was 106 000/µL, and LDH was 283 U/L. One month earlier, his hematocrit was 36% and platelet count was 189 000/µL. Relapse of TTP was not suspected. He had coronary artery bypass graft surgery without complication. On the second day after surgery, his hematocrit was 32% and platelet count was 134 000/µL. He had no subsequent laboratory evaluations and was described as recovering well when he unexpectedly had a seizure, cardiac arrest, and died on the sixth day after surgery. Autopsy documented microvascular thrombi throughout the myocardium but no new myocardial infarction. Death was attributed to relapsed TTP.

A 59-year-old woman relapsed in 1997, 1 year after her initial episode, and was treated with PEX without corticosteroids (our practice at that time). After a response, she continued PEX once per day for 3 days, then every other day for 3 more treatments (also our practice at that time). Her platelet count remained normal (181 000/µL) on the day of her last PEX. Near the end of this PEX she had a sudden seizure and cardiac arrest. Autopsy documented a posterior left ventricle and septal infarction without evidence of TTP.