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Abstract Background: In clinical practice there is little consensus on treating patients with chronic immune thrombocytopenic purpura (ITP) beyond first line therapy with steroids. Objectives: Describe the demographic and disease characteristics of adult ITP patients who receive treatment; Obtain the treatment approach for patients with ITP beyond first line treatment with steroids, with an emphasis on splenectomy; and Evaluate adverse bleeding outcomes associated with ITP. Methods: A retrospective chart review of ITP patients after initial therapy with steroids was conducted. Ten physicians (oncologists and hematologists) were recruited from across Canada and each physician provided at least 5 ITP cases for review. A total of 51 cases were reviewed and patients (> 18 years old) were required to have had more than 1 course of steroids as treatment to be eligible. Results: The average age of patients at diagnosis was 42 (range 3 to 82 years); 37 (73%) of the patients were female, and 37 (73%) were Caucasian. The median platelet count upon presentation was 5×109/L. Median lines of therapy after initial therapy was 3 (range 0 to 6). Second line therapies varied, but most commonly patients underwent splenectomy (43%), followed by continued steroid treatment (16%), steroids plus IV Ig (16%), IV Ig alone (14%), immunosuppressant alone (2%), and anti-D plus steroids (2%). Of the patients reviewed, 40 (78%) eventually underwent splenectomy. Of the 40 splenectomized patients, 27 were splenectomized within the first year of diagnosis and 35 underwent splenectomy during the first 5 years. In addition, 62 of the splenectomies were laparoscopic, and the median hospital stay for all procedures was 5 days (range 1 to 60 days). Immediate failure of splenectomy occurred in 18% of patients, and the one- and five- year relapse/failure rates (defined as platelet count < 30×109/L) were 38% and 55%, respectively. Other therapies following splenectomy included IV Ig, azathioprine, cyclosporine, danazol, mycophenolate, rituximab, vincristine, cyclophosphamide, and anti-D. Only 6% of IV Ig use was for chronic maintenance therapy and 74% of use was for urgent therapy. A total of 61 bleeding events occurred, of which 10 were major (upper GI, mouth, rectal, and nose). Major bleeding events required hospitalization of the patient with an average length of stay of 5 days (range 2 to 14 days). Conclusions: Notwithstanding several limitations, the retrospective chart review suggests that there is wide variation in long-term therapy for patients with chronic ITP in Canada. Splenectomy was the most widely used second line therapy, although 18% of the patients were non-responders and the five-year relapse/failure rate was 55%.

Abstract Background : Many idiopathic thrombotic thrombocytopenia purpura (TTP) patients have severe deficiency of ADAMTS13, an enzyme that cleaves ultralarge von Willebrand multimers. We recently reported that thienopyridine-associated TTP is characterized by an immunologic pathway with severe ADAMTS13 deficiency and a non-immunologic pathway with higher ADAMTS13 activity levels. We now compare findings for idiopathic and thienopyridine-associated TTP patients. Methods : Clinical findings and laboratory findings were evaluated for 51 idiopathic and 39 thienopyridine-associated TTP. Results: Clinical findings were similar between idiopathic and thienopyridine-associated TTP for both severe ADAMTS13 deficient and non-deficient patients. Differences were noted in gender and age, relapse rates, and survival. Conclusion : Among TTP patients with ADAMTS13 deficiency, relapses are frequent in idiopathic TTP patients and Rituximab may be useful, while for thienopyridine-associated TTP patients spontaneous relapse are rare as long as no re-exposure occurs. Among ADAMTS13 non-deficient patients, survival is high following therapeutic plasma exchange (TPE) for idiopathic patients but not for thienopyridine-associated TTP patients. Despite similarities, idiopathic and thienopyridine associated TTP probably have different initiating factors. ADAMTS13 activity and clinical characteristics in idiopathic and thienopyridine-associated TTP Idiopathic severe ADAMTS13 deficiency (n=29) †Thienopyridine severe ADAMTS13 deficiency (n=26) Idiopathic non-severe ADAMTS13 deficiency (n=22) †Thienopyridine non-severe ADAMTS13 deficiency (n=13) *p<0.05 for comparison of severe ADAMTS13 deficiency versus non-severe ADAMTS13 deficiency. †Thienopyridine-associated TTP clinical and presenting neutralizing autoantibody data was summarized from the Journal of the American College of Cardiology publication by Bennett et al. in 2007. ‡Thienopyridine-associated TTP remission autoantibody data was summarized Tsai et al, 2002, Bennett et al, 2000, and Orimo et al, 2002, and included 3 patients. §Data from average of ADAMTS13 deficient and non-deficient cohorts. Mean Age 41 67 47 60 Sex (% female) 79% 54% 86% 39% Platelet count/mm3 (mean)* 18,978 9,269 51,409 35,000 Platelet count <20,000/mm3* 69% 96% 23% 38% Hemoglobin (mg/dl; mean) 8.5 8.3 9.0 8.4 Creatinine (mg/dl; mean)* 1.5 2.2 3.2 3.0 Creatinine >2.5 mg/dl* 11% 27% 48% 46% 30-day survival 96% 85% 90% 62% Long-term relapse* 42% 8% 0% 0% Neutralizing autoantibodies to ADAMTS13 (prior to TPE) § 79% 100% 27% 0% Neutralizing autoantibodies to ADAMTS 13 (measured at remission) § 55% 33%‡ 33% 0%

Abstract Background: Thrombotic thrombocytopenic purpura (TTP) is a rare disorder that presents with microangiopathic hemolytic anemia and thrombocytopenia, fevers, renal insufficiency and neurologic features. We reviewed clinical, laboratory, and outcome data for TTP cases with severely deficient versus non-severely deficient ADAMTS13 activity levels. Methods: Mean and median data were from the Surveillance, Epidemiology and Risk Factors for TTP (SERF-TTP) study group for idiopathic TTP cases, the Canadian Apheresis Group (CAG), and five published series (Zheng 2004, Raife 2004, Vesely 2003 (Oklahoma TTP-HUS Registry), Matsumoto 2004 (Japan Referral Center), Bennett 2007). Results: Compared to TTP cases with near-normal ADAMTS13 activity levels (n= 282), TTP cases with severe ADAMTS13-deficiency (n=185) were more likely to have severe thrombocytopenia, normal renal function and neutralizing ADAMTS13 antibodies. Severe ADAMTS13 deficient TTP cases have better overall survival after therapeutic plasma exchange (TPE) but are more likely to relapse. TTP patients with severe ADAMTS13 deficiency were primarily categorized as idiopathic or ticlopidine-associated, while TTP patients with non-severely deficient ADAMTS13 activity levels were frequently categorized as idiopathic, secondary to drugs (clopidogrel, quinine), stem cell transplantation, or cancer. Conclusions: Severe ADAMTS13 deficiency is most commonly idiopathic, has better survival following TPE, and a 35–40% spontaneous relapse rate. By contrast, non-ADAMTS13 deficient TTP cases are usually associated with an underlying disorder or external insults. Amongst this cohort, four series have 47–62% survival rates and three series, which contain mostly idiopathic cases, have 83–90% survival rates following TPE. From this, we propose that TTP may occur by three possible mechanism; ADAMTS13-deficient (antibody-mediated), an immunologic mediated pathway independent of ADAMTS13 (i.e. quinine) that is responsive to TPE, and endothelial injury related TTP that is unresponsive to TPE. Platelet count mean (x10^9/L) Creatinine mean (mg/dl) ADAMTS13 neutralizing antibodies (%) Survival % Relapse % * <15% ADAMTS13 activity cutoff Severe ADAMTS13 Deficiency (<10–15%) SERF-TTP (n=30) 19 1.3 83 97 41 Zheng (n=16) 19 1.6 44 81 38 Bennett (n=26) 15 85 Oklahoma (n=18) 12 1.8 94 81 38 Raife (n=50) * 13 1.2 92 35 Japan (n=34) 35 91 Canada (n=11) 16 2.4 82 Not Severely Deficient ADAMTS13 Activity (> 15%) SERF-TTP (n=22) 57 3.9 35 90 0 Raife (n=57) * 44 2.7 83 9 Canada (n=17) 57 4.1 88 Zheng (n=13) 40 3.0 0 54 Bennett (n=13) 62 Japan (n=66) 9 62 Oklahoma (n=94 ) 23 47 3

Abstract Thrombotic thrombocytopenic purpura (TTP) is a microvascular occlusive disorder characterized by systemic aggregation of platelets, thrombocytopenia, and mechanical injury to erythrocytes. Between 30% and 80% of TTP cases are associated with ADAMTS13 deficiency. Thienopyridine-derivative anti-platelet agents, ticlopidine and clopidogrel, are the drugs most commonly associated with TTP. The structures differ only by a carboxymethyl side-chain and have no common metabolites. Since 2002, our R01 research project has focused on evaluating thienopyridine-associated TTP. Herein, we present the final results. Clinical and laboratory data were obtained from case reports, the FDA’s MedWatch program, a Japanese national reference laboratory for ADAMTS13 assays, and apheresis centers at Duke University, University of North Carolina, Northwestern University, and the Mayo Clinic. Epidemiologic data for rate estimation for thienopyridine-associated TTP among persons who receive cardiac stents were obtained from international cardiology laboratories. Pharmacovigilance information was obtained from package inserts for the drugs. Most thienopyridine-associated TTP cases are associated with two weeks or more of ticlopidine rather than clopidogrel, are immune-mediated involving neutralizing antibodies to ADAMTS13, resolve with therapeutic plasma exchange (TPE), and have spontaneous relapses. Less frequently, cases are associated with clopidogrel, occur within days of drug initiation, may be a direct result of endothelial cell damage, are less responsive to TPE, and are less likely to recur. Thienopyridine-associated TTP patients with severe deficiency of ADAMTS13 activity have a different profile than those with normal ADAMTS13 levels. Among thienopyridine-associated TTP patients who have ADAMTS13 deficiency, TPE is usually performed for a few days and patients recover without detectable organ damage. In contrast, among thienopyridine-associated TTP patients who do not have ADAMTS13 deficiency, several weeks of TPE is required for recovery, and 30% mortality rates have been reported. Despite similar chemical structures, ticlopidine- and clopidogrel-associated TTP probably occur by different mechanisms and have different clinical presentations and expected outcomes. Clinical Characteristics Onset Platelet Count <20,000 (%) Creatinine ≤2 mg/dl (%) Neurologic Symptoms (%) Mortality With TPE/Without TPE (%) Relapse *p < 0.05 ticlopidine 10%* <2 weeks; 90% 2-12 weeks 84* 28* 28 15/44 Occasional clopidogrel 74%*≤2 weeks; 26% > 2 weeks 60* 55* 32 28/33 Rare Epidemiology, Pharmacovigilance & Basic Science Incidence (cases per treated patients) Safety ADAMTS13 Activity (%) ADAMTS13 Antibodies (%) ticlopidine 1:1,600 “Black Box” warning <10* 90* clopidogrel 1:100,000 package insert warning 50–100* 10*

Background Management of delirium in intensive care units is challenging because effective therapies are lacking. Music is a promising nonpharmacological intervention. Objectives To determine the feasibility and acceptability of personalized music (PM), slow-tempo music (STM), and attention control (AC) in patients receiving mechanical ventilation in an intensive care unit, and to estimate the effect of music on delirium. Methods A randomized controlled trial was performed in an academic medical-surgical intensive care unit. After particular inclusion and exclusion criteria were applied, patients were randomized to groups listening to PM, relaxing STM, or an audiobook (AC group). Sessions lasted 1 hour and were given twice daily for up to 7 days. Patients wore noise-canceling headphones and used mp3 players to listen to their music/audiobook. Delirium and delirium severity were assessed twice daily by using the Confusion Assessment Method for the Intensive Care Unit (CAM-ICU) and the CAM-ICU-7, respectively. Results Of the 1589 patients screened, 117 (7.4%) were eligible. Of those, 52 (44.4%) were randomized, with a recruitment rate of 5 patients per month. Adherence was higher in the groups listening to music (80% in the PM and STM groups vs 30% in the AC group; P = .01), and 80% of patients surveyed rated the music as enjoyable. The median number (interquartile range) of delirium/coma-free days by day 7 was 2 (1-6) for PM, 3 (1-6) for STM, and 2 (0-3) for AC (P = .32). Median delirium severity was 5.5 (1-7) for PM, 3.5 (0-7) for STM, and 4 (1-6.5) for AC (P = .78). Conclusions Music delivery is acceptable to patients and is feasible in intensive care units. Further research testing use of this promising intervention to reduce delirium is warranted.

Introduction The United States Thrombotic Microangiopathy (USTMA) Consortium consists of high-volume US referral centers that are committed to collaborative research in TMAs. The USTMA Immune Thrombotic Thrombocytopenic Purpura (iTTP) registry has compiled retrospective data on demographics, treatments and outcomes in patients with iTTP to create the world's largest database of patients with this rare disease. While there is consensus on the use of therapeutic plasma exchange (TPE) for treatment of iTTP, there are no large randomized trials on which to base use of rituximab. The drug is frequently used for refractory or relapsed iTTP, but is currently being used more frequently for de novo (first episode) iTTP. We queried the USTMA iTTP registry to determine whether relapse free survival (RFS) is superior when rituximab is added to TPE and corticosteroids for treatment of iTTP. We hypothesized that the addition of rituximab would improve RFS at 5 years in both de novo and relapsing iTTP. Methods Following IRB approval at each institution, investigators independently reviewed individual patient records to confirm diagnostic criteria and entered demographic, treatment and outcomes data into the REDCap database housed at the University of North Carolina. The diagnosis of iTTP was defined as ADAMTS13 < 10% or ADAMTS13 < 20% with an inhibitor or antibody detected at any point or a clinical diagnosis of iTTP based on presenting characteristics, response to treatment and/or relapsing phenotype before ADAMTS13 testing became available (N=173). Relapse was defined as a recurrence of iTTP after at least 30 days of remission (recurrence within 30 days was considered an exacerbation, or continuation of the prior episode). To explore the effect of rituximab added to TPE and corticosteroids, we first assessed the treatment effect in de novo iTTP patients and then separately in relapse. We constructed Kaplan-Meier curves to compare RFS for patients treated with rituximab plus corticosteroids versus corticosteroids alone in both groups, and compared RFS at specific time points using the Klein method. To better understand whether other patient variables had an effect on RFS in both de novo episodes and relapses, ordinary (time-to-event) and mixed-effects (recurrent time-to-event) Cox proportional hazards models were used to examine the relationships of treatment, race/ethnicity, sex, age, treatment year, and presenting signs/symptoms with the outcome. Analyses were conducted using R version 3.5.2 (R Foundation for Statistical Computing, Vienna, Austria). Results As of July, 2019, the USTMA database contains 775 unique study patients with a confirmed diagnosis of iTTP with 1397 unique iTTP episodes. The treatment of patients' de novo iTTP episode was available for analysis in 375 patients, 188 of whom were treated with corticosteroids alone, 131 with corticosteroids plus rituximab, and 56 with other therapies. RFS was significantly higher in patients treated with corticosteroids and rituximab compared to those treated with corticosteroids alone at 1 year (0.93 vs. 0.78, p=0.0002) and 3 years (0.82 vs. 0.66, p=0.004) but not 5 years (0.60 vs. 0.56, p=0.39). In addition, the risk of relapse decreased with later treatment year for de novo iTTP (hazard ratio (HR) 0.95, 95% CI 0.92-0.99, p=0.03), consistent with rituximab use increasing over time, and was increased in African Americans compared with Caucasians (HR 1.83, 1.10-3.06, p=0.02). We then explored the treatment effect in all iTTP relapses (743 relapses in 426 patients). Here, a significant (p=0.0007) interaction between treatment and race was found. Among African Americans, we found no difference in RFS when rituximab was added (HR 1.15, 0.81-1.62, p=0.43). However, among Caucasians, RFS was significantly improved when rituximab was added (HR 0.15, 0.06-0.35, p<0.0001). Conclusions For de novo iTTP, adding rituximab to corticosteroids for immunosuppression likely delays but does not prevent relapse. Unlike in de novo disease, in patients with relapsed iTTP, we found a novel and significant interaction between race and treatment: while Caucasians had significantly improved RFS with the addition of rituximab, there was no effect on RFS in African Americans. Further investigation is warranted to determine the mechanisms of this difference in the response to rituximab in relapsed iTTP to improve outcomes in African Americans. Figure Disclosures Marshall: Sanofi: Membership on an entity's Board of Directors or advisory committees. Farland:Sanofi: Membership on an entity's Board of Directors or advisory committees. Metjian:Sanofi: Membership on an entity's Board of Directors or advisory committees. Raval:Bayer, Inc: Research Funding; Sanofi: Membership on an entity's Board of Directors or advisory committees. Liles:Imara: Other: PI on Clinical trial- Sickle cell ; Shire: Other: PI on clinical trial Sickle cell ; Novartis: Other: PI on clinical trial Sickle cell . Baumann Kreuziger:CSL Behring: Consultancy; Vaccine Injury Compensation Program: Consultancy. McCrae:Rigel Pharmaceutical: Membership on an entity's Board of Directors or advisory committees; Sanofi Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Dova Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Pfizer Pharmaceutical: Membership on an entity's Board of Directors or advisory committees. Chaturvedi:Shire/Takeda: Research Funding; Sanofi: Consultancy; Alexion: Consultancy. Zheng:Clotsolution: Other: Co-Founder; Shire/Takeda: Research Funding; Ablynx/Sanofi: Consultancy, Speakers Bureau; Alexion: Speakers Bureau. Cataland:Ablynx/Sanofi: Consultancy, Research Funding; Alexion: Consultancy, Research Funding. Off Label Disclosure: rituximab for immunosuppression in TTP.

Background: Immune thrombotic thrombocytopenic purpura (iTTP) is a potentially fatal hematologic disorder characterized by thrombocytopenia, microangiopathic hemolytic anemia, and ischemic organ impairment. The incidence of iTTP is higher among African-Americans (AA), however, differences in presentation and outcomes have not been fully investigated. In a multi-center cohort of patients with iTTP from the United States Thrombotic Microangiopathy (USTMA) Consortium, we tested the hypothesis that AA race is an independent predictor of poor outcomes including iTTP related mortality and relapse. Methods: We queried data from the USTMA iTTP registry, which currently includes data from 785 individual patients from 15 institutions across the United States. Data from at least one iTTP episode are available for 734 patients. The cohort is 35.1% (N = 272) White, 58.7% (N = 455) African American, 0.4% (N=3) Asian, 1.8% (N=14) Hispanic, and 4.0 % (N=31) other/unknown race. We restricted our analyses to AA and White participants because of small numbers in the other groups. We compared presenting features and treatments using the chi-squared test and t-test for categorical and continuous variables, respectively. A relapse was defined as a recurrent iTTP episode occurring at least 30 days after last therapeutic plasma exchange. To evaluate relapse-free survival, we included only patients enrolled in the registry at their first TTP episode (144 White and 246 AA) since patients presenting with a relapse as their index episode are already confirmed to have relapsing iTTP. Kaplan Meier analysis was used to compare relapse-free survival in White and AA patients, and a Cox regression model was developed to evaluate the independent effect of race on relapse, adjusting for potential confounders including age, sex, and the use of rituximab. Results: Demographics and presenting features of 390 individuals (144 White and 246 AA) presenting with a first episode of iTTP are shown in Table 1. Presenting symptoms including fever, confusion, seizure, memory deficits, stupor, headache, stroke, chest pain, abdominal pain, fatigue, and dark urine were similar between Whites and AA except for petechiae, which were more frequently documented in Whites (28.8% vs 17.7%, p=0.011). Presenting laboratory studies were also comparable though AA had a higher rate of elevated serum troponin (50.6% vs 32.5%, p=0.003), lower hemoglobin level (8.27 ± 0.13 vs 8.81 ± 0.19, p=0.0176) and platelet count (20.3 ± 1.2 vs 26.2 ± 3.2, p=0.0432). In addition to therapeutic plasma exchange and corticosteroids, rituximab was administered to 23.7% of White patients and 22.7% of AA during their first iTTP episode (P=0.815). Median time to platelet count recovery (days of daily plasma exchange until normal platelet count for two consecutive days) was shorter in AA compared with White patients [5 (IQR 4, 10) vs. 8 (IQR 5, 14), log rank P = 0.004]. AA race remained a significant predictor of the shorter time to platelet count recovery [HR 1.44 (95% CI 1.12, 1.85), P=0.004] after adjusting for rituximab therapy [HR 0.60 (95% CI 0.0.46, 0.80), P<0.001], female sex [HR 0.95 (95% CI 0.73, 1.22), P=0.669], age [HR 0.99 (95% CI 0.99, 1.01), P=0.682], platelet count [HR 1.00 (95% CI 0.99, 1.04), P=0.820] and LDH at presentation [HR 1.00 (95% CI 1.00, 1.00), P=0.525]. Death during the first episode occurred in 8.9% of White patients and 5.5% of AA patients (P=0.206). Relapse-free survival after the first episode of iTTP was lower in AA than White patients (Figure 1). AA race was associated with the reduced relapse free survival [HR 1.79 (95% CI 1.08, 2.98), P=0.024] in a Cox regression model adjusted for age [HR 1.00 (95% CI 0.98, 1.01), P=0.683], sex [HR 0.96 (95% CI 0.60, 1.54), P=0.867], and rituximab therapy [HR 0.93 (95% CI 0.55, 1.59), P=0.806]. Conclusion: African Americans with iTTP have a higher relapse rate and shorter relapse free survival after the first episode of the disease compared with Caucasian patients, which is independent of age, sex and rituximab therapy. Contrary to our hypothesis, acute outcomes of iTTP (time to platelet count recovery and mortality) were not worse in AA patients. The factors contributing to the higher relapse rate in AA with iTTP need to be further investigated. Our findings suggest that AA patients may also benefit from closer follow up. Disclosures Farland: Sanofi: Membership on an entity's Board of Directors or advisory committees. Metjian:Sanofi: Membership on an entity's Board of Directors or advisory committees. Raval:Bayer, Inc: Research Funding; Sanofi: Membership on an entity's Board of Directors or advisory committees. Liles:Shire: Other: PI on clinical trial Sickle cell ; Imara: Other: PI on Clinical trial- Sickle cell ; Novartis: Other: PI on clinical trial Sickle cell . Baumann Kreuziger:CSL Behring: Consultancy; Vaccine Injury Compensation Program: Consultancy. McCrae:Dova Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Pfizer Pharmaceutical: Membership on an entity's Board of Directors or advisory committees; Rigel Pharmaceutical: Membership on an entity's Board of Directors or advisory committees; Sanofi Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees. Zheng:Alexion: Speakers Bureau; Ablynx/Sanofi: Consultancy, Speakers Bureau; Clotsolution: Other: Co-Founder; Shire/Takeda: Research Funding. Cataland:Alexion: Consultancy, Research Funding; Ablynx/Sanofi: Consultancy, Research Funding. Chaturvedi:Shire/Takeda: Research Funding; Sanofi: Consultancy; Alexion: Consultancy.

Abstract Abstract 2203 Background: Thrombotic thrombocytopenic purpura (TTP) is frequently characterized by severe ADAMTS13 deficiency, the cause of which is unknown. An important exception is ticlopidine-associated TTP (tc-TTP), the most common drug-induced TTP syndrome. In 1998, a possible association of TTP with ticlopidine was reported. In 1999, two additional series reported this association. In 2000, a fourth study reported severe A DAMTS13 deficiency among six of seven tc-TTP persons- suggesting a causal pathway. All of these reports were from the United States. Recently, we reported characteristics of 186 acquired idiopathic (ai)- TTP patients in Japan with severe ADAMTS13 deficiency, noting that clinical and laboratory findings for ai-TTP patients in Japan differed from those for cohorts of ai-TTP patients in Europe and North America- raising concern that TTP findings vary by region of the world. (PLOS One 2011) We now on report clinical and laboratory characteristics of a cohort of TTP patients from Japan with tc-TTP, and compare these findings to three cohorts of tc-TTP in the United States and one cohort of ai-TTP patients from Japan. Methods: We queried a database of thrombotic microangiopathy patients identified from a national TTP referral laboratory in Japan of cases identified between 1998 and 2008. Severe ADAMTS13 deficiency was characterized by activity levels < 5%. All tc-TTP patients and 186 of 911 ai-TTP patients in the database had severe ADAMTS13 deficiency and first onset of TTP. Comparisons were made to tc-TTP patients reported previously from the United States. Results: Characteristics of ai- TTP with severe ADAMTS13 deficiency in Japan and tc-TTP in Japan and US Conclusions: These data from Japan validate insights about tc-TTP initially proposed in 1998, 1999, and 2000 in the United States. Ticlopidine is a likely cause of TTP, the mechanism is via a cross-reactive antibody to ADAMTS13:AC resulting in formation of an ADAMTS13:INH, and therapeutic plasma exchange is necessary for treatment. Disclosures: Ortel: Eisai: Research Funding; Glaxo SmithKline: Research Funding; Pfizer: Research Funding; Instrumentation Laboratory, Inc: Consultancy, Research Funding; Boehringer Ingelheim: Consultancy. Fujimura:Baxter BioScience: Membership on an entity's Board of Directors or advisory committees; Alexion Pharma: Membership on an entity's Board of Directors or advisory committees.

Abstract Thrombotic microangiopathies (TMAs) are a diverse group of disorders that are characterized by common clinical and laboratory features. The most commonly thought-of TMA is thrombotic thrombocytopenic purpura (TTP). Because of the marked improvement in patient mortality associated with the use of therapeutic plasma exchange (TPE) in TTP, this therapy has been applied to all of the TMAs. The issue, however, is that the pathophysiology varies and in many instances may represent a disorder of the endothelium and not the blood; in some cases, the pathophysiology is unknown. The use of TPE is further obscured by a lack of strong supporting literature on its use, with most consisting of case series and case reports; controlled or randomized controlled trials are lacking. Evidence supporting the use of TPE in the treatment of TMAs (other than TTP and TMA–complement mediated) is lacking, and therefore its role is uncertain. With the greater availability of genetic testing for mutations involving complement regulatory genes and complement pathway components, there seems to be a percentage of TMA cases, other than TMA–complement mediated, in which complement pathway mutations are involved in some patients. The ability of TPE to remove abnormal complement pathway components and replace them with normal components may support its use in some patients with TMAs other than TTP and TMA–complement mediated.