Thrombotic thrombocytopenic purpura-hemolytic uremic syndrome (TTP-HUS) following treatment with deoxycoformycin in a patient with cutaneous T-cell lymphoma (Sezary syndrome): A case report

Onconephrology and Thrombotic Microangiopathy: Looking Beyond the Horizon

Thrombotic microangiopathies (TMAs) represent a complex interaction of endothelial and podocyte biology, nephron physiology, complement genetics, and oncologic therapies with host immunology. The complexity of various factors, such as molecular causes, genetic expressions, and immune system mimicking, along with incomplete penetrance, make it difficult to find a straightforward solution. As a result, there may be variations in diagnosis, study, and treatment approaches, and achieving a consensus can be challenging. Here, we review the molecular biology, pharmacology, immunology, molecular genetics, and pathology of the various TMA syndromes in the setting of cancer. Controversies in etiology, nomenclature, and points requiring further clinical, translational, and bench research are discussed. Complement-mediated TMAs, chemotherapy drug-mediated TMAs, TMAs in monoclonal gammopathy, and other TMAs central to onconephrology practice are reviewed in detail. In addition, established and emerging therapies within the US Food and Drug Administration pipeline subsequently are discussed. Finally, a comprehensive review of critical areas of onconephrology clinical practice is presented as practical value to the clinical practitioner and seeds of investigation to be sown among the community of atypical hemolytic uremic syndrome researchers.

Fatal Microangiopathic Hemolytic Anemia Due to Sézary Syndrome

Sézary syndrome (SS) is a form of cutaneous T-cell lymphoma (CTCL), demonstrating leukemic involvement of malignant T-cells. Known systemic sequelae of SS include hemophagocytic syndrome-induced anemia, normocytic anemia secondary to bone marrow infiltration, and pancytopenia. We report a patient with SS, initially demonstrating widespread morbilliform eruption, who presented with malignancy-related microangiopathic hemolytic anemia (MAHA). Our findings represent a novel presentation of SS that will inform the differential diagnosis and treatment of future SS patients presenting with anemia and thrombocytopenia.

Exploring the binding modes of cordycepin to human adenosine deaminase 1 (ADA1) compared to adenosine and 2'-deoxyadenosine

Cordycepin (3'-deoxyadenosine, abbreviated as COR) from Cordyceps shows a wide range of pharmacological activities, including antioxidant and anticancer effects, therefore representing a potential alternative medicine. However, COR has a short half-life in the human body, where it is metabolized by adenosine deaminase 1 (ADA1). ADA1 helps regulate adenosine levels by deaminating excess adenosine (ADE) and its derivatives, such as 2'-deoxyadenosine (DEO). Understanding binding mechanisms of ADA1 with COR in comparison with its other substrates will play a vital role in improving the bioactivity and lifetime of COR for commercial medicinal use. Recently, the first structure of human ADA1 in complex with DEO was solved. We therefore employed molecular dynamics (MD) simulations to predict structures and dynamics of ADA1 complexing with ADE, DEO, and COR in comparison to a ligand-free (LF) structure. Our data reveal that a large and highly water-exposed binding pocket of ADA1 is responsible for ligand translocation and reorientation. Two possible binding locations (site1 and site2) are identified. The binding affinities of the ligands are ADE > COR > DEO. Furthermore, the movements of two loop regions at the binding pocket entrance, residues 183-193 and 215-230, contribute to gating activity.

Microangiopathic Hemolytic Anemia and Thrombocytopenia in Patients With Cancer

The unexpected occurrence of thrombotic microangiopathy (TMA), characterized by microangiopathic hemolytic anemia and thrombocytopenia, in a patient with cancer requires urgent diagnosis and appropriate management. TMA is a term used to describe multiple syndromes caused by microvascular thrombosis, including thrombotic thrombocytopenic purpura (TTP), Shiga toxin-mediated hemolytic uremic syndrome, and complement-mediated TMA. In patients with cancer, systemic microvascular metastases and bone marrow involvement can cause microangiopathic hemolytic anemia and thrombocytopenia. This occurs most often in patients with known metastatic cancer, but microangiopathic hemolytic anemia and thrombocytopenia may occur unexpectedly in patients without known metastatic disease or be the presenting features of undiagnosed cancer. TMA may also be caused by commonly used chemotherapy agents, either through dose-dependent toxicity or an acute immune-mediated reaction. These causes of TMA must be distinguished from TTP, which results from a severe deficiency of ADAMTS13 and is the most common cause of TMA among adults without cancer. The importance of this distinction is to avoid inappropriate use of plasma exchange, which is associated with major complications. Plasma exchange is the essential treatment for TTP, but it has no known benefit for patients with cancer-induced or drug-induced TMA. We will describe cancer-induced and drug-induced TMA using the experience of the Oklahoma TTP-Hemolytic Uremic Syndrome Registry and data from a systematic review of all published reports of drug-induced TMA. We will illustrate the principles of evaluation and management of these disorders with patients' stories.

Antineoplastic agents and thrombotic microangiopathy

Thrombotic microangiopathy is an uncommon but reported adverse effect of a variety of antineoplastic drugs, including chemotherapy agents such as mitomycin C and gemcitabine, and newer targeted agents such as the vascular endothelial growth factor inhibitors. We present a review of thrombotic microangiopathy associated with antineoplastic agents and its implications in current cancer therapy.

Renal complications in chronic lymphocytic leukemia and monoclonal B-cell lymphocytosis: the Mayo Clinic experience

While the renal complications of plasma cell dyscrasia have been well-described, most information in patients with chronic lymphocytic leukemia and monoclonal B-cell lymphocytosis is derived from case reports. This is a retrospective analysis of patients with chronic lymphocytic leukemia or monoclonal B-cell lymphocytosis who underwent kidney biopsy for renal insufficiency and/or nephrotic syndrome. Between January 1995 and June 2014, 49 of 4,024 (1.2%) patients with chronic lymphocytic leukemia (n=44) or monoclonal B-cell lymphocytosis (n=5) had a renal biopsy: 34 (69%) for renal insufficiency and 15 (31%) for nephrotic syndrome. The most common findings on biopsy were: membranoproliferative glomerulonephritis (n=10, 20%), chronic lymphocytic leukemia interstitial infiltration as primary etiology (n=6, 12%), thrombotic microangiopathy (n=6, 12%), and minimal change disease (n=5, 10%). All five membranoproliferative glomerulonephritis patients treated with rituximab, cyclophosphamide and prednisone-based regimens had recovery of renal function compared to 0/3 patients treated with rituximab with or without steroids. Chronic lymphocytic leukemia infiltration as the primary cause of renal abnormalities was typically observed in relapsed/refractory patients (4/6). Thrombotic microangiopathy primarily occurred as a treatment-related toxicity of pentostatin (4/6 cases), and resolved with drug discontinuation. All cases of minimal change disease resolved with immunosuppressive agents only. Renal biopsy plays an important role in the management of patients with chronic lymphocytic leukemia or monoclonal B-cell lymphocytosis who develop renal failure and/or nephrotic syndrome.

Drug-induced thrombotic microangiopathy: Experience of the Oklahoma Registry and the BloodCenter of Wisconsin

Many drugs have been reported to cause thrombotic microangiopathy (TMA), often described as thrombotic thrombocytopenic purpura (TTP) or hemolytic-uremic syndrome (HUS). We recently established criteria to evaluate the evidence for a causal association of a drug with TMA and then we systematically reviewed all published reports of drug-induced TMA (DITMA) to determine the level of evidence supporting a causal association of the suspected drug with TMA. On the basis of this experience, we used these evaluation criteria to assess the Oklahoma TTP-HUS Registry patients who had been previously categorized as drug-induced, 1989-2014. We also reviewed the experience of the BloodCenter of Wisconsin with testing for drug-dependent antibodies reactive with platelets and neutrophils in patients with suspected immune-mediated DITMA, 1988-2014. Among 58 patients in the Oklahoma Registry previously categorized as drug-induced (15 suspected drugs), 21 patients (three drugs: gemcitabine, pentostatin, quinine) had evidence supporting a definite association with TMA; 19 (90%) of the 21 patients had quinine-induced TMA. The BloodCenter of Wisconsin tested 40 patients with suspected DITMA (eight drugs); drug-dependent antibodies, supporting a definite association with TMA, were identified in 30 patients (three drugs: oxaliplatin, quinine, vancomycin); 28 (93%) of the 30 patients had quinine-induced TMA. Combining the data from these two sources, 51 patients (five drugs) have been identified with evidence supporting a definite association with TMA. DITMA was attributed to quinine in 47 (92%) of these 51 patients.

Inhibition of adenosine deaminase (ADA)-mediated metabolism of cordycepin by natural substances

Cordycepin, which is an analogue of a nucleoside adenosine, exhibits a wide variety of pharmacological activities including anticancer effects. In this study, ADA1- and ADA2-expressing HEK293 cells were established to determine the major ADA isoform responsible for the deamination of cordycepin. While the metabolic rate of cordycepin deamination was similar between ADA2-expressing and Mock cells, extensive metabolism of cordycepin was observed in the ADA1-expressing cells with K_m and V_max values of 54.9 μmol/L and 45.8 nmole/min/mg protein. Among five natural substances tested in this study (kaempferol, quercetin, myricetin, naringenin, and naringin), naringin strongly inhibited the deamination of cordycepin with K_i values of 58.8 μmol/L in mouse erythrocytes and 168.3 μmol/L in human erythrocytes. A treatment of Jurkat cells with a combination of cordycepin and naringin showed significant cytotoxicity. Our in silico study suggests that not only small molecules such as adenosine derivatives but also bulky molecules like naringin can be a potent ADA1 inhibitor for the clinical usage.

Gemcitabine-related thrombotic microangiopathy: a single-centre retrospective series

INTRODUCTION

Thrombotic microangiopathy (TMA) has been reported as a complication of chemotherapy. Many antineoplastic agents have been linked to TMA, gemcitabine being one of the most frequently cited as related to this syndrome.

METHODS

A retrospective search for chemotherapy-induced TMA cases among gemcitabine users in a single oncology centre from January 2009 to September 2012 was performed.

RESULTS

Three cases of gemcitabine-induced TMA were reported, from a total of 264 patients (incidence: 1·13%) who received the drug. From the three cases reported, two (66%) patients died as a consequence of the syndrome.

DISCUSSION

These findings are compatible with previous analyses, which report an incidence of gemcitabine-associated TMA ranging from 0·008 to 2·2% and mortality rates from 15 to 90%. Unlike previously reported, however, cumulative dose was not predictive of risk.

CONCLUSION

Gemcitabine-induced TMA is an underdiagnosed condition characterized by high mortality rates. Attention should be called for a higher level of awareness to provide early diagnosis and proper treatment.

Thrombotic microangiopathy with skin localization secondary to cytarabine-daunorubicin association: report of a case

The thrombotic microangiopathy is a syndrome characterized by the combination of mechanical hemolytic anemia, peripheral thrombocytopenia, and organ failure of variable severity. In addition to the idiopathic form, several cases are identified as secondary to pregnancy, infections, disease systems, organ transplants, and cancer. Other forms are secondary to drugs including antimitotics. We report the case of a patient followed for acute myelogenous leukemia. She received induction chemotherapy combining daunorubicin and cytarabine, complicated by thrombotic thrombocytopenic purpura.

Prophylaxis of graft-versus-host disease in unrelated donor transplantation with pentostatin, tacrolimus, and mini-methotrexate: a phase I/II controlled, adaptively randomized study

PURPOSE

Acute graft-versus-host disease (aGVHD) is a major cause of morbidity and mortality after matched unrelated, related, or mismatched related donor hematopoietic stem-cell transplantation (HSCT). Improved GVHD prevention methods are needed. Pentostatin, an adenosine deaminase inhibitor, leads to lymphocyte depletion with low risk of myelosuppression. We hypothesized that addition of pentostatin to GVHD prophylaxis with tacrolimus and mini-methotrexate may improve outcomes, and we conducted a Bayesian adaptively randomized, controlled, dose-finding study, taking into account toxicity and efficacy.

PATIENTS AND METHODS

Success was defined as the patient being alive, engrafted, in remission, without GVHD 100 days post-HSCT and no grade ≥ 3 GVHD at any time. Patients were randomly assigned to pentostatin doses of 0, 0.5, 1.0, 1.5, and 2.0 mg/m(2) with drug administered on HSCT days 8, 15, 22, and 30. Eligible patients were recipients of mismatched related (n = 10) or unrelated (n = 137) donor HSCT.

RESULTS

Median age was 47 years. Thirty-seven, 10, 29, 61, and 10 patients were assigned to the control and four treatment groups, respectively, with comparable baseline characteristics. Pentostatin doses of 1.0 and 1.5 mg/m(2) had the highest success rates (69.0% and 70.5%) versus control (54.1%). The posterior probabilities that the success rates were greater with 1.5 mg/m(2) or 1.0 mg/m(2) versus control are 0.944 and 0.821, respectively. Hepatic aGVHD rates were 0%, 17.2%, and 11.1%, respectively, for 1.5 mg/m(2), 1.0 mg/m(2), and control groups. No grades 3 to 4 aGVHD occurred in 11 HLA-mismatched recipients in the 1.5 mg/m(2) group.

CONCLUSION

Pentostatin increased the likelihood of success as defined here, and should be further investigated in larger randomized, confirmatory studies.

Vascular Toxicity of Antineoplastic Agents

Among the various deleterious effects of cancer chemotherapy, vascular toxicity is the least well recognized. This lack of recognition may be because the vasculotoxic phenomena are not unique to antineoplastic agents, can occur in patients without exposure to these agents, and the fact cancer itself may produce a hypercoagulable state. As a result, many vascular events either go unnoticed, are ignored, and/or are attributed to the underlying malignancy. Many antineoplastic therapies are associated with various vascular phenomena that range from simple phelibitis to lethal microangiopathy. Recognition of these events is important to minimize the morbidity and even prevent unnecessary deaths. Herein we review the vascular syndromes that have been reported in association with antineoplastic agents.

Chemical-induced atrial thrombosis in NTP rodent studies

Cardiac thrombosis, one of the causes of sudden death throughout the world, plays a principal role in several cardiovascular diseases, such as myocardial infarction and stroke in humans. Data from studies of induction of chemical thrombosis in rodents help to identify substances in our environment that may contribute to cardiac thrombosis. Results for more than 500 chemicals tested in rodents in 2-year bioassays have been published as Technical Reports of the National Toxicology Program (NTP) http://ntp-server.niehs.nih.gov/index. We evaluated atrial thrombosis induced by these chemical exposures and compared it to similarly induced lesions reported in the literature. Spontaneous rates of cardiac thrombosis were determined for control Fischer 344 rats and B6C3F1 mice: 0% in rats and mice in 90-day studies and, in 2-year studies, 0.7% in both genders of mice, 4% in male rats, and 1% in female rats. Incidences of atrial thrombosis were increased in high-dosed groups involving 13 compounds (incidence rate: 20-100%): 2-butoxyethanol, C.I. Direct Blue 15, bis(2-chloroethoxy)methane, diazoaminobenzene, diethanolamine, 3,3'-dimethoxybenzidine dihydrochloride, hexachloroethane, isobutene, methyleugenol, oxazepam, C.I. Pigment Red 23, C.I. Acid Red 114, and 4,4'-thiobis(6-t-butyl-m-cresol). The main localization of spontaneously occurring and chemically induced thromboses occurred in the left atrium. The literature survey suggested that chemical-induced atrial thrombosis might be closely related to myocardial injury, endothelial injury, circulatory stasis, hypercoagulability, and impaired atrial mechanical activity, such as atrial fibrillation, which could cause stasis of blood within the left atrial appendage, contributing to left atrial thrombosis. Supplementary data referenced in this paper are not printed in this issue of Toxicologic Pathology. They are available as downloadable files at http://taylorandfrancis.metapress.com/openurl.asp?genre=journal&issn=0192-6233. To access them, click on the issue link for 33(5), then select this article. A download option appears at the bottom of this abstract. In order to access the full article online, you must either have an individual subscription or a member subscription accessed through www.toxpath.org.

The Oklahoma Thrombotic Thrombocytopenic Purpura-Hemolytic Uremic Syndrome Registry: a program for patient care, education and research

The Oklahoma Thrombotic Thrombocytopenic Purpura-Hemolytic Uremic Syndrome (TTP-HUS) Registry was created by collaboration of the Oklahoma Blood Institute and the Colleges of Medicine and Public Health of the University of Oklahoma Health Sciences Center, combining their respective strengths of community service, patient care, education, and clinical research methodology. The organization of the Registry is based on the fundamental principles of patient-oriented research: 1) all consecutive patients are identified at a uniform time early in the course of their disease; 2) analysis of clinical data requires quantitative and reproducible definitions; 3) patient follow-up is complete; and 4) therefore the data are generalizable to community practice. A summary of 15 years experience with 301 consecutive patients is presented. Some of these results and interpretations are different from other case series. These differences emphasize the distinct perspective of the Registry that includes all patients in the community who have had a clinical diagnosis of TTP or HUS and for whom plasma-exchange treatment was requested. The Oklahoma TTP-HUS Registry provides educational and research opportunities, in addition to improved patient care, and serves as a model for productive collaboration of community blood centers and universities.

Results of a phase II multicenter trial of pentostatin and rituximab in patients with low grade B-cell non-Hodgkin's lymphoma: an effective and minimally toxic regimen

This study explored the efficacy and toxicity of the combination of pentostatin and rituximab, effective single agents in low-grade non-Hodgkin's lymphoma (NHL). Sixty patients with previously treated low-grade NHL were enrolled. Except for day 1, both drugs were administered weekly for 4 weeks, with week 5 off. During week 1 (day 1) only rituximab was given; subsequent weekly treatments included both drugs. Patients received a minimum of 2 five-week cycles in order to be evaluable for efficacy. Responses were evaluated on week 5 of cycle 2. If partial response (PR) or stable disease (SD) responses were noted, 2 additional cycles were administered. Final evaluations were done on week 5 of cycle 4. Of 60 patients, 58.3% had an Eastern Cooperative Oncology Group performance status (PS) of 0, and 41.7% had PS of 1; 31.7% and 51.7% had stage III or stage IV disease, respectively. Histology included follicular center, follicular, grade I (45%), II (21.7%), III (1.7%), and small lymphocytic (31.7%). Seventeen patients had prior chemotherapy, but no patients had received prior pentostatin or rituximab. Median age was 60.3 years (range, 32.5-84.7 years). Among 57 evaluable patients, 77% responded (22.3% complete response [CR], 3.5% unconfirmed CR, 35.1% PR, and 10.5% unconfirmed PR); 19.3% had SD, and 8.8% progressive disease (PD). Response rate among previously untreated patients was 83% versus 63% in previously treated patients. Median duration of response was 11 months (range, 2.3-22.2 months); median time to progression was 15 months (range, < 1-25 months). Neutropenia was the only adverse event experienced by >/= 10% of patients. Six deaths were caused by PD, and one death each was caused by acute respiratory distress, possibly related respiratory failure, and cardiac toxicity. These results suggest the combination of pentostatin/rituximab is well tolerated and active in low-grade lymphoma.

The Oklahoma thrombotic thrombocytopenic Purpura-Hemolytic uremic syndrome (TTP-HUS) registry: a community perspective of patients with clinically diagnosed TTP-HUS

The Oklahoma Thrombotic Thrombocytopenic Purpura-Hemolytic Uremic Syndrome (TTP-HUS) Registry enrolls all consecutive patients for whom plasma exchange treatment is requested for clinically diagnosed TTP-HUS within a defined geographic region. During 14.5 years, from January 1, 1989 until June 30, 2003, 301 patients have been enrolled; follow-up is complete on 300 patients. Clinical categories have been designated based on associated conditions and potential etiologies; presenting features and clinical outcomes have been defined to allow comparisons between groups. ADAMTS-13 activity was measured on 142 (88%) of 161 consecutive patients enrolled from 1995 to 2001. Only 13% of all patients, and 33% of patients with idiopathic TTP-HUS, had severe ADAMTS-13 deficiency (<5% activity). The presenting features and clinical outcomes of patients with severe ADAMTS-13 deficiency were heterogeneous and not distinct from patients without severe ADAMTS-13 deficiency. These data suggest that severe ADAMTS-13 deficiency does not detect all patients who may be appropriately diagnosed with TTP-HUS and who may respond to plasma exchange treatment. Prospective data from consecutive patients are essential to translate new observations on pathogenesis into improved patient care.

Thrombotic thrombocytopenic purpura associated with bone marrow metastasis and secondary myelofibrosis in cancer

To examine the relationship between cancer and development of thrombotic microangiopathy (TM), the medical records of patients with known TM were examined in one institution from January 1981 to December 2002. Nine out of 93 patients with the established diagnosis of TM had active cancer. All nine of those patients had thrombotic thrombocytopenic purpura (TTP). Among those patients, two patients received chemotherapy prior to the development of TTP. Six of the seven patients who received no chemotherapy had extensive bone marrow metastasis and secondary myelofibrosis. There were two patients each with breast cancer, lung cancer, and stomach cancer. Severe anemia and thrombocytopenia with leukoerythroblastosis were prominent clinical features in all six patients. Four patients had neurological (mental) changes and three developed fever, but none had significant renal dysfunction. Upon establishing the diagnosis of TTP, four patients were treated with exchange plasmapheresis (EP) and two patients were treated with chemotherapy because there were no neurological changes. Three patients achieved complete remission of TTP, one with EP alone and two with chemotherapy. The one patient who achieved remission with EP alone was later treated with chemotherapy and survived for 2 1/2 years. The other three patients treated with EP alone died within 2 months after the diagnosis of TTP. Since TTP occurred in association with bone marrow metastasis and myelofibrosis in six patients among seven chemotherapy-untreated cancer patients, this marrow change was considered to be the possible cause of the development of TTP. It is recommended that all cancer patients with unexplained anemia and thrombocytopenia be evaluated for the coexistence of bone marrow metastasis and TTP.

A chemically induced rat model of hemolysis with disseminated thrombosis

Although hemolytic anemia and thrombosis, which can be serious or even lethal, are often encountered in daily common practice, their pathogenesis has remained obscure, partially because of the absence of appropriate models. Here we present a unique chemically induced rat model of hemolytic anemia and disseminated thrombosis in which the organs developing infarction are comparable to those seen in humans. We exposed male and female Fischer F344 rats to two, three, or four daily doses of 2-butoxyethanol (BE) at 250 mg/kg body weight and examined for hemolysis and histopathological evidence of disseminated thrombosis on d 2, 3, 4, and 29. Time-course BErelated erythrocytic changes were statistically significant in both sexes. Evidence of thrombosis and infarction was seen mainly in females dosed more than once with widespread thrombotic crisis after two or three dosing, likely explicable by the more significant morphological changes in erythrocytes and hemolysis observed in this gender. We documented thrombosis and infarction in the heart, brain, lungs, eyes, and bones. Our model with its list of target organs similar to that observed in human diseases characterized by hemolysis and thrombosis [for example, thalassemia, sickle cell disease (SCD), paroxysmal nocturnal hemoglobinuria (PNF), disseminated intravascular coagulation (DIC), thrombotic thrombocytopenic purpura (TTP), and hemolytic uremic syndrome (HUS)] suggests that it can be an excellent tool to study the pathogenesis of such complications.

How I treat patients with thrombotic thrombocytopenic purpura–hemolytic uremic syndrome

Thrombotic thrombocytopenic purpura (TTP) and hemolytic uremic syndrome (HUS) are, in adults, clinically and pathologically indistinguishable except for the severity of renal failure. They are best described as a single disorder, TTP-HUS, because the diagnostic evaluation and initial management are the same. Treatment with plasma exchange, available for more than 20 years, has dramatically altered the course of disease in adults with TTP-HUS. Plasma exchange has improved survival rates from 10% to between 75% and 92%, creating urgency for the initiation of treatment. This has resulted in decreased stringency of diagnostic criteria, which in turn has resulted in a broader spectrum of disorders for which the diagnosis of TTP-HUS is considered. Long-term follow-up has revealed increasing frequencies of relapse and of chronic renal failure. Although the increased survival rate is dramatic and recent advances in understanding the pathogenesis of these syndromes are remarkable, clinical decisions remain empirical. Therefore, the management decisions for patients with suspected TTP-HUS rely on individual experience and opinion, resulting in many different practice patterns. Multipractice clinical trials are required to define optimal management.

How I treat patients with thrombotic thrombocytopenic purpura–hemolytic uremic syndrome

Thrombotic thrombocytopenic purpura (TTP) and hemolytic uremic syndrome (HUS) are, in adults, clinically and pathologically indistinguishable except for the severity of renal failure. They are best described as a single disorder, TTP-HUS, because the diagnostic evaluation and initial management are the same. Treatment with plasma exchange, available for more than 20 years, has dramatically altered the course of disease in adults with TTP-HUS. Plasma exchange has improved survival rates from 10% to between 75% and 92%, creating urgency for the initiation of treatment. This has resulted in decreased stringency of diagnostic criteria, which in turn has resulted in a broader spectrum of disorders for which the diagnosis of TTP-HUS is considered. Long-term follow-up has revealed increasing frequencies of relapse and of chronic renal failure. Although the increased survival rate is dramatic and recent advances in understanding the pathogenesis of these syndromes are remarkable, clinical decisions remain empirical. Therefore, the management decisions for patients with suspected TTP-HUS rely on individual experience and opinion, resulting in many different practice patterns. Multipractice clinical trials are required to define optimal management.