Predicting Risk for Relapse in Patients Who Have Recovered from Thrombotic Thrombocytopenic Purpura (TTP).
Authors: Johnson Kristina K. , Terrell Deirdra R. , Lammle Bernhard , Hovinga Johanna Kremer , George James N. , Vesely Sara K. 
Published: April 2020

Abstract
The greatest concern for patients who have recovered from an acute episode of TTP is the risk for relapse. We have analyzed the experience of The Oklahoma TTP-HUS Registry to estimate the risk for relapse and to identify the time to relapse and factors that determine the risk for relapse. The Registry has complete follow-up data on 333 of 335 consecutive patients who had their first episode of clinically diagnosed TTP, 1989–2005. Patients who were discovered to have an alternative diagnosis for their signs of TTP, patients whose TTP followed bone marrow transplantation and patients with drug-induced TTP were not analyzed. Among the 219 remaining patients, 172 achieved a remission (defined as survival &gt;30 days after the last plasma exchange treatment) and were at risk for relapse. Among these 172 patients, 22 (21%) of 107 patients with idiopathic TTP relapsed and 5 (8%) of 65 patients in other clinical categories (pregnancy associated, bloody diarrhea prodrome, autoimmune disease) relapsed (P&lt;0.02). ADAMTS13 has been measured at the time of diagnosis of the first episode in 92% of consecutive patients since November 1995. Among patients who had ADAMTS13 activity &lt;10% at the time of their initial diagnosis, 13 of 30 (43%) relapsed compared to 2 of 81 (2%) patients who had initial ADAMTS13 activity of ≥10% (P&lt;.001). These 30 patients have been followed a median of 63 months (range, 6–124 months). Nine of the 13 patients who have relapsed have had only 1 relapse; the others have had 2–4 relapses. Nine patients had their first relapse within one year of their initial episode; the others had their first relapse within 4 years. Eleven patients followed &gt; 4 years have never relapsed.
Time to First Relapse in 30 patients with ADAMTS13 Activity &lt; 10%. Time to First Relapse in 30 patients with ADAMTS13 Activity &lt; 10%.
The Table compares the clinical features of the 13 ADAMTS13 deficient patients who relapsed to the 17 patients who did not relapse.
Comparison between ADAMTS13 deficient patients who did and did not relapse Clinical features Relapse No Relapse P n=13 n=17 Data are median values from the initial episode. Severe neurologic abnormalities were coma, stroke, seizure, or focal signs. Age (years) 46 39 0.04 Race (% black) 62% 29% 0.08 Sex (% men) 38% 0% 0.01 Severe neurological abnormality (%) 46% 35% 0.55 Hematocrit (%) 21% 21% 0.82 Platelets (/μL) 7,000 10,000 0.68 Creatinine (mg/dL) 1.0 1.0 0.66 LDH (U/L) 1363 1434 0.62 ADAMTS13 inhibitor (% moderate/strong) 38% 53% 0.43 Number of plasma exchanges 22 14 0.23
CONCLUSIONS: Patients with idiopathic TTP have a greater risk for relapse than other patients. Patients who initially have severely deficient ADAMTS13 activity (&lt;10%) have the highest risk for relapse. Most initial relapses occur within the first year following the initial episode; all occurred within 4 years. Most patients have only 1 relapse. Among patients who have ADAMTS13 deficiency (&lt;10%), the only features that predict a greater risk for relapse are older age and male sex.