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

The G1691A Mutation of the Factor V Gene (Factor V Leiden) and the G20210A Mutation of the Prothrombin Gene as Risk Factors in Thrombotic Microangiopathies

Factor V Leiden (FVL) mutation and prothrombin G20210A mutation are common hereditary risk factors for venous thrombosis. In the current study, 40 patients (mean age ± standard deviation, 35 ± 11 years) and 764 healthy control subjects (mean age ± standard deviation, 37 ± 14 years) were enrolled to assess the potential role of these mutations in the manifestation of thrombotic microangiopathies. Compared with controls, neither the heterozygous FVL mutation (7.5% vs 8.5%; P = 1) nor the heterozygous prothrombin mutation (2.5% vs 2.8%; P = 1) was more prevalent in the patients. The findings do not support a significant role of FVL and prothrombin mutations as risk factors for the manifestation of thrombotic microangiopathies. Thus, screening for these mutations does not allow the identification of individuals at increased risk for these rare thrombotic disorders.

The Homozygous Leu Variant of the Factor XIII Val34Leu Polymorphism as a Risk Factor for the Manifestation of Thrombotic Microangiopathies

The 34 Leu (100T) variant of the factor XIII Val34Leu (G100T-) polymorphism slows down fibrinolysis and has been proposed as a thrombotic risk factor. In this pilot study, we enrolled 40 patients (mean age ± SD = 38 ± 11 years) and 728 controls to assess the role of this genetic variant for the manifestation of thrombotic microangiopathies. From the genotype prevalences, an increased manifestation risk for carriers of the TT genotype (homozygous Leu variant) of the factor XIII Val34Leu (G100T-) polymorphism was calculated (odds ratio [OR] = 2.44; 95% confidence interval [CI] = 0.8-7.6; P = .11). This association was statistically significant for patients with thrombotic thrombocytopenic purpura—hemolytic-uremic syndrome (TTP-HUS) (OR = 6.6; 95% CI = 1.7-25.9; P = .006). Our data suggest a role of the homozygous Leu variant of the factor XIII Val34Leu polymorphism in the manifestation of thrombotic microangiopathies. Decreased fibrinolysis in the presence of this genetic variant provides a plausible explanation for this association.

TTP/HUS and prognosis: the syndrome and the disease(s)

Patients presenting with the syndrome of microangiopathic hemolysis and thrombocytopenia, without Shiga toxin-associated colitis, have thrombotic thrombocytopenic purpura/hemolytic uremic syndrome (TTP/HUS). Prognosis for TTP/HUS has changed over time from a fatal disorder associated with the classic pentad to a syndrome associated with 80% survival in the plasma exchange era. A growing number of mechanisms, including but not exclusive to severe ADAMTS13 deficiency, are now understood to result in this syndrome, and the prognosis of patients with TTP/HUS is related to many additional factors. This update on prognosis explores recent registry data studying both acquired idiopathic and also familial or recurrent forms of TTP/HUS, to delineate how mortality varies by underlying disease mechanism. This paper also explores the association between mortality and clinical presenting features, as well as whether the case is a primary or relapsed presentation. Recent data support an understanding of TTP/HUS as a heterogeneous syndrome with variable mortality, and with specific subgroups demonstrating an excellent outcome.

The thrombotic thrombocytopenic purpura and hemolytic uremic syndromes: evaluation, management, and long-term outcomes experience of the Oklahoma TTP-HUS Registry, 1989-2007

The Oklahoma thrombotic thrombocytopenic purpura-hemolytic uremic syndrome (TTP-HUS) Registry, an inception cohort of 382 consecutive patients with TTP-HUS, provides a complete community perspective of these syndromes. TTP, as defined by thrombocytopenia and microangiopathic hemolytic anemia without an alternative etiology, is the appropriate term for all adults. These limited diagnostic criteria are supported by the presenting features of patients with ADAMTS13 deficiency, in whom both neurologic and renal abnormalities are uncommon. HUS is the appropriate term for children who fulfill these diagnostic criteria and who also have renal failure. These definitions are consistent with current management: plasma exchange is the essential treatment for most adults; supportive care is sufficient for children with HUS. Plasma exchange treatment has decreased the mortality of TTP from 90 to 10%. Patients with acquired autoimmune ADAMTS13 deficiency may also require immunosuppressive treatment to achieve a durable remission. Recovery has revealed previously unrecognized long-term risks. Recurrent acute episodes occur in approximately 40% of patients with acquired ADAMTS13 deficiency; most relapses occur within the first year and most patients have only one relapse. Adults with TTP of any etiology have a high risk for persistent minor cognitive abnormalities.

Clinical outcomes after platelet transfusions in patients with thrombotic thrombocytopenic purpura

BACKGROUND

Reports of deterioration and death after platelet (PLT) transfusions in patients with thrombotic thrombocytopenic purpura (TTP) have led to recommendations that they should not be given except for life-threatening hemorrhage.

STUDY DESIGN AND METHODS

Published reports of PLT transfusions in patients with TTP were systematically reviewed and data from the Oklahoma TTP-HUS Registry, an inception cohort of 382 consecutive patients, 1989 through 2007, were analyzed.

RESULTS

A systematic review identified 34 publications describing outcomes of patients with TTP after PLT transfusions: 9 articles attributed complications to PLT transfusions, 4 suggested that they may be safe, and 21 articles did not comment about a relation between PLT transfusions and outcomes. Fifty-four consecutive patients from the Oklahoma TTP-HUS Registry were prospectively analyzed. ADAMTS13 activity was less than 10 percent in 47 patients; also included were 7 patients whose activity was not measured but who may have been deficient. Thirty-three (61%) patients received PLT transfusions. The frequency of death was not different between the two groups (p = 0.971): 8 (24%) patients who received PLT transfusions died (thrombosis, 5; hemorrhage, 1; sepsis, 2) and 5 (24%) patients who did not receive PLT transfusions died (thrombosis, 4; hemorrhage, 1). The frequency of severe neurologic events was also not different (p = 0.190): 17 (52%) patients who received PLT transfusions (in 5 of these 17 patients, neurologic events only occurred before PLT transfusions) and 7 (33%) patients who did not receive PLT transfusions.

CONCLUSION

Evidence for harm from PLT transfusions in patients with TTP is uncertain.

Thrombotic thrombocytopenic purpura related to severe ADAMTS13 deficiency in children

Thrombotic thrombocytopenic purpura (TTP) related to a severely deficient activity of the von Willebrand factor cleaving protease, ADAMTS (A Disintegrin And Metalloprotease with ThromboSpondin type 1 repeats) 13, is a life-threatening event, the onset of which may occur as early as childhood. TTP is either inherited (Upshaw-Schulman syndrome) via ADAMTS13 gene mutations (neonatal onset) or acquired via anti-ADAMTS13 autoantibodies (childhood onset). TTP is due to platelet- and von-Willebrand-factor-rich thrombi of the microvasculature, inducing mechanical hemolytic anemia, consumption thrombocytopenia, and multivisceral ischemia. Clinical course consists of relapsing acute events triggered mostly by infections, associated icterus and hyperbilirubinemia, severe hemolytic anemia with schistocytosis and a negative Coombs test, severe thrombocytopenia, and sometimes symptoms related to visceral ischemia (renal failure, central nervous system vascular events, other organ failure). The recently available ADAMTS13 laboratory investigation combining measurement of ADAMTS13 activity in plasma, search for an ADAMTS13 circulating inhibitor, and anti-ADAMTS13 IgG and ADAMTS13 gene sequencing is a crucial addition to TTP diagnosis. Plasma exchanges are first-line treatment of acquired TTP, combined with steroids and immunosuppressive drugs. Curative treatment of acute events in Upshaw-Schulman syndrome relies on plasma infusions (provider of active ADAMTS13). Guidelines for preventive treatment of relapses are not clearly established but should associate plasmatherapy and caution to triggers of relapses. Therapeutic perspectives are focused on the development of concentrated plasma-derived ADAMTS13 or recombinant ADAMTS13.

Lessons learned from the Oklahoma thrombotic thrombocytopenic purpura-hemolytic uremic syndrome registry

The Oklahoma TTP-HUS Registry provides a complete community perspective of thrombotic thrombocytopenic purpura (TTP). This is possible because plasma exchange is the essential treatment for TTP and the Oklahoma Blood Institute provides all plasma exchange procedures for a region encompassing most of the State, including 58 of Oklahoma's 77 counties. The Registry is an inception cohort of consecutive patients for whom plasma exchange treatment was requested for a diagnosis of either TTP or hemolytic uremic syndrome (HUS). All 382 patients identified from January 1, 1989 to December 31, 2007 have consented to be enrolled. Complete follow-up is available for 380 of 382 patients. Patients are described both by clinical categories, related to their associated conditions and clinically apparent etiologies, and by the presence of severe ADAMTS13 deficiency. ADAMTS13 activity has been measured on 235 (93%) of 254 patients since 1995. Registry data have provided new perspectives on the definition and diagnoses of these syndromes as well as their outcomes. Long-term follow-up has documented that relapse is common among patients with ADAMTS13 deficiency but rarely occurs in patients without ADAMTS13 deficiency. Long-term follow-up has also documented persistent abnormalities of health-related quality-of-life and cognitive function. In addition to providing new perspectives on the natural history of these syndromes, The Oklahoma TTP-HUS Registry provides a support group for our patients, information about evaluation and management for community physicians, and a resource for research and educational programs.

Treating TTP/HUS with plasma exchange: a single centre's 25-year experience

Thrombotic thrombocytopenic purpura/Haemolytic uremic syndrome (TTP/HUS) is a thrombotic microangiopathy with a 6-month mortality rate of 16-29%. The present study described the clinical features, treatment regime and 6-month all-cause mortality rate of TTP/HUS patients at the London Health Sciences Centre (LHSC), Canada. Data for this retrospective cohort study were obtained from inpatient and outpatient records for all patients referred for plasma exchange therapy at LHSC, Canada between 1981 and 2006. Patients (n = 110) were categorized as: idiopathic primary (38%) or relapsed (16%), and secondary responsive (30%) or non-responsive (16%). Mortality data were available for all but three patients. The all-cause 6-month mortality rate was 19% overall and was 12% and 26% among idiopathic and secondary TTP/HUS patients, respectively. No mortality events occurred among the 17 idiopathic patients who relapsed. Relapsed patients had the least severe presenting characteristics, the fastest response time, and experienced significant improvement in the severity of clinical features between the first and final presentation. These findings suggest an excellent outcome for relapsed TTP/HUS patients. Patient education, surveillance, and aggressive plasma exchange therapy are hypothesized to improve the likelihood of survival: these hypotheses should be tested in a randomized controlled trial.

Are prothrombotic variants of platelet glycoprotein receptor polymorphisms involved in the pathogenesis of thrombotic microangiopathies?

Thrombotic microangiopathies are life-threatening disorders characterized by vascular microthromboses, schistocytic hemolytic anemia, and thrombocytopenia. Although recent research has partially explained the pathogenesis of these rare entities, the determinants contributing to the onset and modulating the severity of thrombotic microangiopathies are largely unknown. The present study assessed the putative role of prothrombotic platelet receptor polymorphisms in thrombotic microangiopathies that have been found to be associated with premature onset of myocardial infarction in predisposed individuals. Thirty-four consecutive patients admitted with the diagnosis of thrombotic microangiopathy and 759 healthy subjects were enrolled. Genotyping of the human platelet antigen (HPA) 2 an the Kozak sequence polymorphism of GP Ibalpha of the platelets' von Willebrand factor receptor glycoprotein (GP) Ib-V-IX, the HPA-1 and the HPA-3 polymorphism of the fibrinogen receptor GP IIb-IIIa (integrin alpha(IIb)beta( 3)) and the HPA-5 and GP Ia 807 C/T polymorphism of the collagen receptor GP Ia-IIa (integrin alpha(2)beta(1)) were determined according to standard procedures. As a result, no significant differences in the prevalence of prothrombotic variants of platelet-receptor polymorphisms between patients and healthy control subjects were observed. However, although not significant, the prothrombotic bb genotype of the HPA-1 polymorphism was more prevalent in the patients. The findings do not provide evidence that platelet receptor polymorphisms are determinants for the onset of thrombotic microangiopathies or predispose to a more severe course. Along with this observation, screening for respective platelet-receptor polymorphisms does not appear to contribute to risk stratification of affected patients.

Thrombotic microangiopathy after allogeneic hematopoietic stem cell transplantation: an autopsy study

BACKGROUND

Posttransplantation thrombotic microangiopathy (PTMA) is a complication of allogeneic hematopoietic stem cell transplantation (HSCT). However, limited autopsy data are available, and it remains unclear whether PTMA is a discrete clinical and pathologic entity. The aims of this autopsy study were to determine the correlation between clinical and pathologic diagnosis of PTMA, to define the precise morphologic spectrum of PTMA, and to seek for potential etiologic factors.

METHODS

The study included 20 consecutive patients with HSCT autopsied at the University of Oklahoma, between 1994 and 2005. Applying strict clinical-laboratory criteria, 6 patients were diagnosed clinically with PTMA and treated with plasma exchange. Clinical variables, including underlying disease, conditioning regimen, stem cell donor status, duration and serum level of cyclosporine, infections, and acute graft versus host disease were compared statistically in patients with histologic signs of PTMA (n=8) with those without PTMA (n=12).

RESULTS

PTMA was verified histologically in all 6 patients with a clinical diagnosis of PTMA but only 2 of the 14 patients who were not clinically diagnosed had histologic evidence of PTMA (P<0.0001). Kidneys were affected in all 8 patients with PTMA, and limited extrarenal involvement by PTMA was observed in 3 of these 8 patients. No statistically significant differences in relevant clinical and morphologic variables were identified between the PTMA and non-PTMA groups.

CONCLUSIONS

This study documents a strong correlation between the clinical and morphologic diagnosis of PTMA. The kidney is the primary target of PTMA, with dominant glomerular and arteriolar involvement. The etiology is likely to be multifactorial.

Cyclosporin and plasma exchange in thrombotic thrombocytopenic purpura: long-term follow-up with serial analysis of ADAMTS13 activity

We hypothesized that cyclosporin (CSA) as adjunct to plasma exchange (PE) improves the efficacy of PE in idiopathic thrombotic thrombocytopenic purpura (TTP) via suppression of the antibody inhibitor of ADAMTS13. Our preliminary findings with CSA and PE as the upfront treatment of TTP suggested that the addition of CSA to PE significantly decreased the exacerbation (disease recurrence within 30 d of the last PE) rates compared to a cohort that received corticosteroids and PE as their upfront therapy of TTP. We present an updated analysis with long-term follow-up of 18 patients with idiopathic TTP treated with concurrent CSA and PE with analysis of serial measurements of ADAMTS13 activity, antigen and inhibitor concentration in the context of clinical outcome data. Overall, 16/18 (89%) patients achieved remission, similar to historical remission rates in idiopathic TTP with PE with only one patient suffering an exacerbation. Clinical responses correlated with improvements in ADAMTS13 activity and suppression of the antibody inhibitor of ADAMTS13. These data suggest that the efficacy of CSA is at least in part related to its suppression of the antibody inhibitor of ADAMTS13 and a subsequent improvement in ADAMTS13 activity and antigen.

Twice-daily plasma exchange for patients with refractory thrombotic thrombocytopenic purpura: the experience of the Oklahoma Registry, 1989 through 2006

BACKGROUND

Twice-daily plasma exchange has been used for patients with thrombotic thrombocytopenic purpura (TTP) who are unresponsive to treatment with daily plasma exchange for many years but with no clear evidence of effectiveness.

STUDY DESIGN AND METHODS

The 18 years' experience of The Oklahoma TTP-HUS (hemolytic-uremic syndrome) Registry, 1989 through 2006, with twice-daily plasma exchange for 31 episodes of TTP in 28 patients is reported. A definite response to twice-daily plasma exchange was defined a priori as a platelet (PLT) count increase after twice-daily plasma exchange on two separate occasions during the treatment of a single episode of TTP, with no change of other treatments. A possible response was defined as a PLT count increase after initiation of twice-daily plasma exchange only once with or without change of other treatments.

RESULTS

A definite response to twice-daily plasma exchange occurred in 3 episodes (three patients), 27 episodes had a possible response, and 1 episode had no response. The three patients with a definite response had ADAMTS13 activities of 5, 6, and 12 percent and all had an inhibitor; the patient with no response was subsequently determined to have Rocky Mountain spotted fever.

CONCLUSION

Twice-daily plasma exchange was typically considered in acutely ill patients who had initially responded but then severe thrombocytopenia recurred, often with new neurologic abnormalities, while continuing daily plasma exchange. In three patients, twice-daily plasma exchange appeared to be beneficial. In most patients, a benefit of twice-daily plasma exchange could not be clearly documented because other treatments were initiated or intensified.

Gemcitabine-associated thrombotic thrombocytopenic purpura

Gemcitabine-associated thrombotic thrombocytopenic purpura (TTP) is a rare complication of gemcitabine treatment with a incidence ranging from 0.015% to 1.4%. Clinically, this disease manifests as haemolytic anaemia, thrombocytopenia, and renal insufficiency; hypertension and neurological and pulmonary symptoms are also known complications. The risk of TTP increases as the cumulative dose of gemcitabine approaches 20,000 mg/m(2). The pathophysiology of this disease entity is unknown although several theories, involving both immune and non-immune mechanisms, have been proposed. The most effective treatment is discontinuation of gemcitabine, the provision of antihypertensive medications as needed, and consideration of plasmapheresis or use of immunoadsorption column in severe cases.

Thrombotic thrombocytopenic purpura induced by trimethoprim-sulfamethoxazole in a Jehovah's Witness

We report a case of Thrombotic Thrombocytopenic Purpura occurring as an allergic response to trimethoprim-sulfamethoxazole therapy (Bactrim, Septra) in a Jehovah's Witness patient. The patient presented with fulminant microangiopathic hemolytic anemia and thrombocytopenia within 48 hr of initiating therapy with trimethoprim-sulfamethoxazole. Other symptoms of drug hypersensitivity included nausea, vomiting, urticarial rash, and leukopenia. Because of her religious faith, the patient was supported without plasma therapy with use of intravenous immunoglobulin, steroids, rituximab, and erythropoietin.

Prognostic value of anti-ADAMTS 13 antibody features (Ig isotype, titer, and inhibitory effect) in a cohort of 35 adult French patients undergoing a first episode of thrombotic microangiopathy with undetectable ADAMTS 13 activity

To study both the pathophysiologic and the prognostic value of ADAMTS13 in thrombotic microangiopathies (TMAs), we enrolled a cohort of 35 adult patients combining a first acute episode of TMA, an undetectable (below 5%) ADAMTS13 activity in plasma, and no clinical background such as sepsis, cancer, HIV, and transplantation. All patients were treated by steroids and plasma exchange, and an 18-month follow-up was scheduled. Remission was obtained in 32 patients (91.4%), and 3 patients died (8.6%) after the first attack. At presentation, ADAMTS13 antigen was decreased in 32 patients (91.4%), an ADAMTS13 inhibitor was detectable in 31 patients (89%), and an anti-ADAMTS13 IgG/IgM/IgA was present in 33 patients (94%). The 3 decedent patients were characterized by the association of several anti-ADAMTS13 Ig isotypes, including very high IgA titers, while mortality was independent of the ADAMTS13 inhibitor titer. In survivors, ADAMTS13 activity in remission increased to levels above 15% in 19 patients (59%) but remained undetectable in 13 patients (41%). Six patients relapsed either once or twice (19%) during the follow-up. High levels of inhibitory anti-ADAMTS13 IgG at presentation were associated with the persistence of an undetectable ADAMTS13 activity in remission, the latter being predictive for relapses within an 18-month delay.

Disseminated malignancy misdiagnosed as thrombotic thrombocytopenic purpura: A report of 10 patients and a systematic review of published cases

BACKGROUND

Patients with disseminated malignancy who present with microangiopathic hemolytic anemia and thrombocytopenia may be misdiagnosed as thrombotic thrombocytopenic purpura (TTP), resulting in inappropriate plasma exchange treatment, a procedure with major risk, and delay of appropriate chemotherapy.

PURPOSE

To assess clinical features that may distinguish occult disseminated malignancy from TTP.

PATIENTS AND METHODS

We report the 17-year experience of The Oklahoma TTP-Hemolytic-Uremic Syndrome (HUS) Registry (1989-2005) and a systematic review of previously published case reports.

RESULTS

Ten of 351 patients in the Oklahoma Registry who were initially diagnosed with TTP and treated with plasma exchange were subsequently discovered to have disseminated malignancy. Only one patient had a history of cancer. In these 10 patients, neurologic abnormalities, hematocrit, platelet count, and serum creatinine were not different from the 133 concurrent patients with idiopathic TTP. Patients with disseminated malignancy had a longer duration of symptoms, more frequent presence of respiratory symptoms, higher lactate dehydrogenase levels, and more often failed to respond to plasma exchange treatment. Diagnosis of malignancy was made by bone marrow biopsy in six patients but not until autopsy in two patients. A systematic literature review identified 19 additional patients, reported from 1965 to 2005, in whom TTP or HUS was initially suspected and systemic malignancy was subsequently discovered. Fourteen different malignant disorders were diagnosed in these 29 patients.

CONCLUSIONS

Occult disseminated malignancy may mimic TTP. A search for systemic malignancy, including a bone marrow biopsy, is appropriate when patients with TTP have atypical clinical features or fail to respond to plasma exchange.

Successful repeat therapy with rituximab for relapsed thrombotic thrombocytopenic purpura

Thrombotic thrombocytopenic purpura (TTP) is a life-threatening disease that is treated successfully with therapeutic plasma exchange (TPE) and often with corticosteroids; however, almost one third of TTP patients have treatment failures that require either long-term TPEs or other adjunct therapies. Recent insights into the autoimmune-pathophysiology of this disease provide the rationale for immune-based therapies. Cumulative evidence suggests that rituximab, an anti-CD20 antibody that depletes B-cells temporarily, is an effective therapy in patients with refractory or relapsing TTP. We report here two patients with chronic relapsing TTP who were treated successfully with rituximab. However, both experienced TTP relapse following sustained and prolonged remissions for 21 and 37 months, respectively. They responded favorably with repeat therapy with rituximab. The benefits of rituximab treatment for refractory or relapsing TTP as well as in the prevention of recurrences are discussed.

A randomized, controlled Phase III trial of therapeutic plasma exchange with fresh-frozen plasma (FFP) prepared with amotosalen and ultraviolet A light compared to untreated FFP in thrombotic thrombocytopenic purpura

BACKGROUND

Photochemical treatment of fresh-frozen plasma (FFP) with amotosalen and ultraviolet (UV) A light (PCT FFP) results in inactivation of a broad spectrum of pathogens while retaining coagulation factor activity, antithrombotic proteins, and von Willebrand factor-cleaving protease (VWF-CP) activity.

STUDY DESIGN AND METHODS

A randomized, controlled, double-blind Phase III trial was conducted with PCT FFP or control FFP for therapeutic plasma exchange (TPE) in patients with thrombotic thrombocytopenic purpura (TTP). Owing to the rarity of this diagnosis, the trial was not powered to demonstrate small differences between treatment groups. Patients were treated with study FFP for a maximum of 35 days until remission was achieved (for a maximum of 30 daily study TPEs with no remission) plus an additional 5 days after remission.

RESULTS

Among the 35 patients treated, the primary endpoint, remission within 30 days, was achieved by 14 of 17 (82%) PCT patients and 16 of 18 (89%) control patients (p = 0.658) The 90 percent confidence interval for treatment difference in remission rate for test - control was (-0.291 to 0.163). Time to remission, relapse rates, time to relapse, total volume and number of FFP units exchanged, and number of study TPEs were not significantly different between groups. Improvement in VWF-CP and inhibitors was similar for both groups. The overall safety profile of PCT FFP was similar to control FFP. No antibodies to amotosalen neoantigens were detected.

CONCLUSION

The comparable results between treatment groups observed from this small trial suggest that TPE with PCT FFP was safe and effective for treatment of TTP.

A classification of hemolytic uremic syndrome and thrombotic thrombocytopenic purpura and related disorders

The diagnostic terms hemolytic uremic syndrome (HUS) and thrombotic thrombocytopenic purpura (TTP) are based on historical and overlapping clinical descriptions. Advances in understanding some of the causes of the syndrome now permit many patients to be classified according to etiology. The increased precision of a diagnosis based on causation is important for considering logical approaches to treatment and prognosis. It is also essential for research. We propose a classification that accommodates both a current understanding of causation (level 1) and clinical association in cases for whom cause of disease is unclear (level 2). We tested the classification in a pediatric disease registry of HUS. The revised classification is a stimulus to comprehensive investigation of all cases of HUS and TTP and is expected to increase the proportion of cases in whom a level 1 etiological diagnosis is confirmed.

Rituximab therapy for thrombotic thrombocytopenic purpura: a proposed study of the Transfusion Medicine/Hemostasis Clinical Trials Network with a systematic review of rituximab therapy for immune-mediated disorders

The rationale for immunosuppressive therapy of thrombotic thrombocytopenic purpura (TTP) was established by observations that TTP may be caused by autoantibodies to ADAMTS13. Patients with high-titer autoantibodies to ADAMTS13 may have a higher mortality, and survivors may require prolonged plasma exchange therapy in spite of adjunctive glucocorticoid treatment. More intensive immunosuppressive therapy with rituximab may provide benefit for many of these patients. The Transfusion Medicine/Hemostasis Clinical Trials Network is developing a randomized, clinical trial to test the hypothesis that addition of rituximab to standard treatment of TTP with plasma exchange and glucocorticoids will decrease initial treatment failure rates as well as subsequent relapses over the following 3 years. To provide the background data for this clinical trial, a systematic review of all published reports on rituximab treatment of immune-mediated disorders was performed. Twelve articles have reported 27 patients treated with rituximab for TTP, with benefit described in 25 (93%) of the patients. Additional reports have described rituximab treatment of 37 other immune-mediated disorders, with clinical response in most patients. These observations from small uncontrolled case series provide the background and rationale for a randomized clinical trial to establish the role of rituximab in the management of patients with TTP.

Local experience with thrombotic thrombocytopenic purpura from the western part of Turkey

Thrombotic thrombocytopenic purpura (TTP) is a fatal disorder if left untreated. Therapeutic plasma exchange (PE) has resulted in excellent remission and survival rates in these patients but there is a need for alternative immuno-modulatory treatments in unresponsive patients. We present a descriptive, retrospective study of 25 (14 female, 11 male) adult patients admitted to our hematology unit with TTP. The patients' median age was 32 years. The patients were treated with immediate PE and a standard dose of corticosteroid therapy. Twenty percent of the patients obtained a complete response after the addition of Intravenous immuno-globulin (IVIg). Improvement of clinical status, platelet counts and serum LDH levels were seen after a median 13, 14 and 3.5 PE sessions, respectively. The mortality rate was 12%. One patient has a chronic relapsing form of TTP and two patients have relapsed. All the other patients are still in complete remission after a median of 7 years of follow-up. Although PE therapy is life-saving and the application of early corticosteroid treatment could obtain early and durable responses, addition of other immuno-modulatory treatments are needed in unresponsive patients. The use of IVIg could result in a dramatic response.

Cleavage of ultra-large von Willebrand factor by ADAMTS-13 under flow conditions

von Willebrand factor (VWF) is a critical ligand for platelet adhesion and aggregation. It is synthesized and released as multimers composed of various numbers of monomers. When first released from the storage granules of endothelial cells, VWF multimers are rich in the ultra-large (UL) forms that spontaneously bind the GP Ib-IX complex and aggregate platelets. These prothrombotic ULVWF multimers are rapidly cleaved by the metalloprotease ADAMTS-13 (A Disintegrin and Metalloprotease with ThromboSpondin motif) to smaller and much less active forms. Recently, several methods have been developed to measure ADAMTS-13 activity in vitro and to link its deficiency to thrombotic thrombocytopenic purpura. Correlations between the structure and functions of the metalloprotease have also been extensively studied using recombinant technologies. However, questions remain regarding the proper substrate for the metalloprotease, the time and location of ULVWF proteolysis, and the role of fluid shear stress. In this brief review, we have discussed a potential model for ULVWF proteolysis by ADAMTS-13 in vivo. In this model, ULVWF is anchored to the surface of endothelial cells to form string-like structures under fluid shear stress. Such an elongated conformation facilitates ULVWF cleavage by exposing either the cleavage or binding sites for the metalloprotease. When ADAMTS-13 is deficient, the uncleaved ULVWF accumulates in plasma and on endothelial cells to capture platelets. This leads to platelet aggregation and thromboembolism. Dissecting the process of ULVWF proteolysis is important for not only understanding the pathophysiology of thrombotic microangiopathies, but also developing more effective means to treat these deadly diseases.

The incidence of thrombotic thrombocytopenic purpura-hemolytic uremic syndrome: all patients, idiopathic patients, and patients with severe ADAMTS-13 deficiency

BACKGROUND

Accurate estimates of the incidence of thrombotic thrombocytopenic purpura (TTP) are important to assess the resources required for current treatments as well as to anticipate the need to develop new treatments. Previous estimates have been indirect and have not reported data on patients with ADAMTS-13 deficiency.

OBJECTIVE

To determine the incidence of patients with TTP-hemolytic uremic syndrome (HUS) in three categories: all patients with clinically suspected TTP-HUS, patients with idiopathic TTP-HUS, and patients with severe ADAMTS-13 deficiency.

METHODS

Incidence rates were estimated from the Oklahoma TTP-HUS Registry, analyzing all 206 consecutive patients from January 1, 1996 to June 30, 2004 who were treated with plasma exchange for their initial episode of clinically suspected TTP-HUS. ADAMTS-13 activity was measured in 186 (90%) of the 206 patients.

RESULTS

The age-sex-race standardized annual incidence rates were 11.29 x 10(6) (95% CI: 9.70-12.88) for all patients with clinically suspected TTP-HUS; 4.46 x 10(6) (95% CI: 3.43-5.50) for patients with idiopathic TTP-HUS; and 1.74 x 10(6) (95% CI: 1.06-2.41) for patients with severe ADAMTS-13 deficiency (<5% activity). In all three categories, the incidence rates were greater for women and for blacks. For patients with severe ADAMTS-13 deficiency, the age-sex standardized incidence rate ratio of blacks to non-blacks was 9.29 (95% CI: 4.33-19.93).

CONCLUSIONS

Accurate incidence rate estimates for all patients with clinically suspected TTP-HUS, idiopathic TTP-HUS, and TTP associated with severe ADAMTS-13 deficiency have been determined. The greater incidence among women and blacks is comparable with their increased risk for other autoimmune disorders.

Von Willebrand factor-cleaving protease activity remains at the intermediate level in thrombotic thrombocytopenic purpura

A 59-year-old woman, diagnosed with chronic myelogenous leukemia (chronic phase) and treated with interferon-alpha for 13 years, developed renal failure. Renal biopsy showed thrombotic thrombocytopenic purpura, but intensive therapy including plasma exchange and steroid administration was not effective. The activity of von Willebrand factor-cleaving protease was detectable at the intermediate level (15-46%) during the clinical course, suggesting that this case was not compatible with the previously reported pattern of idiopathic or drug-induced thrombotic thrombocytopenic purpura, but with the pattern associated with malignant disease or immunological disorders. Further studies to determine the effects of interferon-alpha on endothelial cells in chronic myelogenous leukemia patients are needed.

Proportion of drug-related serious rare blood dyscrasias: estimates from the Berlin Case-Control Surveillance Study

Drugs are an important cause of serious rare blood dyscrasias. To estimate the proportion of drug-related cases, we used data from the ongoing Berlin Case-Control Surveillance Study. The analysis included a total of 171 cases. The number of cases in which a drug etiology was assessed as at least "possible" was n = 29 (97%) for acute agranulocytosis, n = 4 (0.21%) for aplastic anemia, n = 8 (26%) for immune hemolytic anemia, n = 20 (25%) for immune thrombocytopenia, and n = 2 (20%) for thrombotic thrombocytopenic purpura/hemolytic uremic syndrome. Our analysis suggests that a substantial fraction of blood dyscrasias may be attributable to drug therapy.

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.

Pregnancy outcomes after recovery from thrombotic thrombocytopenic purpura-hemolytic uremic syndrome

BACKGROUND

Recurrent thrombotic thrombocytopenic purpura-hemolytic uremic syndrome (TTP-HUS) during a subsequent pregnancy is an important concern because pregnancy may increase the risk for relapse.

STUDY DESIGN AND METHODS

Outcomes of all pregnancies after recovery from TTP-HUS in the Oklahoma TTP-HUS Registry, a cohort of 301 consecutive patients during the period of 1989 through 2003, were assessed and compared to the total published experience.

RESULTS

In the Oklahoma Registry, 3 of 7 (43%) women with idiopathic TTP-HUS, 2 of 11 (18%) women who were pregnant/postpartum, and 0 of 1 (0%) woman with a bloody diarrhea prodrome at their initial presentation were diagnosed with TTP-HUS during a subsequent pregnancy; all 5 women recovered. In published reports, 10 of 11 (91%) women with idiopathic TTP-HUS and 11 of 18 (61%) women who were pregnant/postpartum at their initial presentation, and all 11 (100%) women with congenital TTP-HUS were diagnosed with TTP-HUS during a subsequent pregnancy. Rates of recurrence in the Oklahoma Registry may be less because of case report bias for exceptional patients. Recurrent TTP-HUS was difficult to diagnose because other pregnancy-related complications were frequent.

CONCLUSIONS

Although pregnancies in these women were often complicated, a future pregnancy may be a safe and appropriate decision for women who have recovered from TTP-HUS.

Recent advances in thrombotic thrombocytopenic purpura

Thrombotic thrombocytopenic purpura (TTP) is characterized by microangiopathic hemolytic anemia and thrombocytopenia, accompanied by microvascular thrombosis that causes variable degrees of tissue ischemia and infarction. Intravascular coagulation is not a prominent feature of the disorder. Plasma exchange can induce remissions in approximately 80% of patients with idiopathic TTP, but patients have a much worse prognosis when thrombotic microangiopathy is associated with cancer, certain drugs, infections, or tissue transplantation. Recently, acquired autoimmune deficiency of a plasma metalloprotease named ADAMTS13 was shown to cause many cases of idiopathic TTP. This review describes our current understanding of how to use this knowledge clinically. In Section I, Dr. Joel Moake describes the presentation of thrombotic microangiopathy, emphasizing the pathophysiology of idiopathic TTP. Platelets adhere to ultra-large (or "unusually large") von Willebrand factor (ULVWF) multimers that are immobilized in exposed subendothelial connective tissue and secreted into the circulation in long "strings" from stimulated endothelial cells. ADAMTS13 cleaves ULVWF multimers within growing platelet aggregates under flowing conditions, and this normally limits platelet thrombus formation. If ADAMTS13 is absent, either congenitally or due to acquired autoantibodies, platelet-rich microvascular thrombosis proceeds unchecked and TTP ensues. Plasma exchange is effective therapy for idiopathic TTP, probably because it replenishes the deficient ADAMTS13 and removes some of the pathogenic autoantibodies and endothelial-stimulating cytokines. Some patients have a type of thrombotic microangiopathy after transplantation/chemotherapy but do not have severe ADAMTS13 deficiency. The pathogenesis of their disease must differ but remains poorly understood. In Section II, Dr. Toshiyuki Miyata describes recent advances in assay methods that should facilitate routine laboratory testing of ADAMTS13 for patients with thrombotic microangiopathy. ADAMTS13 cleaves a single Tyr-Met bond in domain A2 of the VWF subunit. ADAMTS13 assays based on the cleavage of plasma VWF multimers have been used extensively but require considerable time and expertise to perform. A recombinant substrate containing 73 amino acid residues of VWF domain A2 has been devised that allows short incubation times and rapid product detection by gel electrophoresis or immunoassay. These results should encourage the development of even simpler assays that can be performed in most clinical laboratories. In Section III, Dr. James George provides an update on the long-term prospective study of thrombotic microangiopathy in the Oklahoma TTP-HUS Registry. At presentation, the clinical distinction between idiopathic TTP, various forms of secondary thrombotic microangiopathy, and even Shiga toxin-associated hemolytic uremic syndrome (HUS) can be problematic because the symptoms and laboratory findings often overlap. Consequently, plasma exchange usually is administered to any patient with thrombotic microangiopathy if there is doubt about the cause. The role of ADAMTS13 testing in choosing therapy remains uncertain, but the results do appear to have prognostic significance. Severe ADAMTS13 deficiency is specific for idiopathic TTP and identifies a subgroup with a high likelihood of response to plasma exchange, and high-titer ADAMTS13 inhibitors correlate strongly with a high risk of relapsing disease. Patients with normal ADAMTS13 activity have a much worse prognosis, although many factors probably contribute to this difference. Longitudinal study of these patients will continue to clarify the relationship of ADAMTS13 deficiency to the clinical course of thrombotic microangiopathy.