Treatment of thrombotic thrombocytopenic purpura with plasma

Thrombotic thrombocytopenic purpura: 100 years of research on Moschcowitz syndrome

ABSTRACT

In the 100 years since Eli Moschcowitz reported the first case of thrombotic thrombocytopenic purpura (TTP), there has been remarkable awareness and progress in the diagnosis and management of this rare blood disorder. This progress initially was the result of careful clinical observations followed by well thought-out therapeutic interventions, with dual goals of both improving outcomes and discerning the pathophysiology of TTP. The discovery of the ADAMTS13 protease set in motion the efforts to more accurately define the specific etiologies of thrombotic microangiopathies (TMAs) based on objective, scientific data rather than clinical characterizations alone. This accurate differentiation led to better and more revealing clinical trials and advancements in the treatment of TTP and other TMAs. Further advances followed and included improvements in immune-suppressive therapy and targeted therapies of immune-mediated TTP (iTTP; caplacizumab) and congenital TTP (cTTP; recombinant ADAMTS13). The longitudinal study of patients with TTP revealed the unexpected risk for long-term complications in both patients with iTTP and those with cTTP in remission. Ongoing studies aim to further understand the prevalence, mechanisms, and appropriate screening for these mood disorders, neurocognitive deficits, and cardiovascular complications that develop at remarkably high rates and are associated with a decreased life expectancy. These discoveries are a result of the collaborative efforts of investigators worldwide that have been fostered by the frequent interactions of investigators via the International TTP Working Group meetings and TMA workshops held regularly at international meetings. These efforts will support the rapid pace of discovery and improved understanding of this rare disease.

Hereditary TTP/Upshaw-Schulman syndrome: the ductus arteriosus controls newborn survival

Hereditary TTP (hTTP), termed Upshaw-Schulman syndrome, is an ultra-rare disorder caused by a severe deficiency of plasma ADAMTS13 activity that allows circulation of ultra-large von Willebrand factor (UL-VWF) multimers. The greatest risk for hTTP is in their first days after birth, when 35-50% of patients will have severe hemolysis, jaundice, and thrombocytopenia. It is often fatal without effective treatment. In utero, fetal blood flowing from the pulmonary artery through the ductus arteriosus (DA) to the aorta is under low-shear-force. At birth, blood flow through the DA reverses to a left-to-right shunt, and the diameter of the DA begins to decrease due to hyper-oxygenated blood and decreased plasma prostaglandin E2. This causes turbulent circulation that unfolds UL-VWF, allowing platelet aggregation. If the DA closes promptly, hTTP newborns survive, but if it remains patent, turbulent circulation persists, triggering microvascular thrombosis. hTTP is commonly diagnosed as hemolytic disease of the fetus and newborn (HDFN) caused by anti-red cell antibodies and treated with exchange blood transfusion, which prevents kernicterus even when the diagnosis of hTTP is missed. The diagnosis of newborn-onset hTTP should be considered because HDFN does not cause severe thrombocytopenia, which might be effectively treated with recombinant ADAMTS13.

Laboratory investigation and diagnosis of thrombotic thrombocytopenic purpura

Thrombotic thrombocytopenic purpura (TTP) is a rare and potentially fatal disease for which rapid diagnosis is crucial for patient outcomes. Deficient activity (< 10%) of the liver enzyme, ADAMTS13, is the pathophysiological hallmark of TTP, and measurement of the enzyme activity can establish the diagnosis of TTP with high accuracy. Thus, along with the clinical history, appropriate laboratory assessment of a suspected case of TTP is essential for diagnosis and treatment. Here, we present a review of the available laboratory tests that can assist clinicians in establishing the diagnosis of TTP, with special focus on ADAMTS13 assays, including the measurement of the antigen and activity, and detection of autoantibodies to ADAMTS13.

Therapeutic modalities in thrombotic thrombocytopenic purpura management among Jehovah's Witness patients: A review of reported cases

INTRODUCTION

Devout members of the Jehovah's Witness faith flatly refuse transfusions of white blood cells, red blood cells, platelets, and plasma. The latter agent is a mainstay in the treatment of thrombotic thrombocytopenic purpura (TTP). Alternative treatment options for Jehovah's Witness patients are needed and reviewed herein.

METHODS

Cases of TTP treatment among Jehovah's Witnesses were obtained from the published literature. Key baseline and clinical data were extracted and summarized.

RESULTS

A total of 13 reports spanning a 23-year period and 15 TTP episodes were identified. Median (IQR) age was 45.5 (29.0-57.5) and 12/13 (93%) patients were female. Neurologic symptoms were present in 7/15 (47%) episodes at presentation. Disease confirmation with ADAMTS13 testing was present in 11/15 (73%) of episodes. Corticosteroids and rituximab were employed in 13/15 (87%) and 12/15 (80%) of cases, respectively, with apheresis-based therapy employed in 9/15 (60%) episodes. For eligible cases, caplacizumab was used in 4/5 (80%) episodes; average time to platelet response was shortest in these cases. Sources of exogenous ADAMTS13 accepted by patients in this series included cryo-poor plasma, FVIII concentrate, and cryoprecipitate.

CONCLUSIONS

Successful management of TTP within the boundaries of the Jehovah's Witness faith is possible.

Clinical Manifestations, Current and Future Therapy, and Long-Term Outcomes in Congenital Thrombotic Thrombocytopenic Purpura

Congenital thrombotic thrombocytopenic purpura (cTTP) is an extremely rare disease characterized by the severe deficiency of a disintegrin and metalloproteinase with thrombospondin type 1 motifs 13 (ADAMTS13), caused by ADAMTS13 mutations. While ADAMTS13 supplementation by fresh frozen plasma (FFP) infusion immediately corrects platelet consumption and resolves thrombotic symptoms in acute episodes, FFP treatment can lead to intolerant allergic reactions and frequent hospital visits. Up to 70% of patients depend on regular FFP infusions to normalize their platelet counts and avoid systemic symptoms, including headache, fatigue, and weakness. The remaining patients do not receive regular FFP infusions, mainly because their platelet counts are maintained within the normal range or because they are symptom-free without FFP infusions. However, the target peak and trough levels of ADAMTS13 to prevent long-term comorbidity with prophylactic FFP and the necessity of treating FFP-independent patients in terms of long-term clinical outcomes are yet to be determined. Our recent study suggests that the current volumes of FFP infusions are insufficient to prevent frequent thrombotic events and long-term ischemic organ damage. This review focuses on the current management of cTTP and its associated issues, followed by the importance of upcoming recombinant ADAMTS13 therapy.

Thrombotic Thrombocytopenic Purpura: From 1972 to 2022 and Beyond

This review tells the story of my personal experience with thrombotic thrombocytopenic purpura (TTP). It begins with my first encounter with TTP 50 years ago when 2 sisters presented 2 years apart, both pregnant and both died. At that time, I knew nothing about hereditary TTP (hTTP), the risks of pregnancy, or effective treatments. In 1991, a year after I moved to Oklahoma, therapeutic plasma exchange (TPE) was established as an effective treatment. With the availability of effective treatment, the number of patients presenting with suspected TTP soared. The diagnosis of TTP was imprecise. I worked with the Oklahoma Blood Institute (OBI) to understand the management of TTP. Because the OBI provided all TPE procedures for most of Oklahoma, we saw all consecutive patients within a defined geographic area who were identified at a uniform time early in the course of their TTP, without selection or referral bias. It was an inception cohort; this became the Oklahoma TTP Registry. In 2001, we began a very successful collaboration with the University of Bern, Switzerland, to measure ADAMTS13 activity in all of our patients. From our patients, we learned that acquired, autoimmune TTP (iTTP) is a chronic disease with risks for cognitive impairment and depression. Recognition in 2012 of three sisters with hTTP was reminiscent of the beginning of my story. hTTP has risks for multiple severe morbidities, beginning at birth and especially during pregnancy. Future management of both iTTP and hTTP will be more effective and more convenient.

TTP: From empiricism for an enigmatic disease to targeted molecular therapies

The 100th anniversary of the first description of Thrombotic Thrombocytopenic Purpura (TTP) as a disease by Dr. Eli Moschcowitz approaches. For many decades, TTP remained mostly a mysterious fatal condition, where diagnosis was often post-mortem. Initially a pentad of symptoms was identified, a pattern that later revealed to be fallible. Sporadic observations led to empiric interventions that allowed for the first impactful breakthrough in TTP treatment, almost 70 years after its first description: the introduction of plasma exchange and infusions as treatments. The main body of knowledge within the field was gathered in the latest three decades: patient registries were set and proved crucial for advancements; the general mechanisms of disease have been described; the diagnosis was refined; new treatments and biomarkers with improvements on prognosis and management were introduced. Further changes and improvements are expected in the upcoming decades. In this review, we provide a brief historic overview of TTP, as an illustrative example of the success of translational medicine enabling to rapidly shift from a management largely based on empiricism to targeted therapies and personalized medicine, for the benefit of patients. Current management options and present and future perspectives in this still evolving field are summarized.

Morbidities and mortality in patients with hereditary thrombotic thrombocytopenic purpura

Hereditary thrombotic thrombocytopenic purpura (hTTP) is a rare disorder caused by severe ADAMTS13 deficiency. Major morbidities and death at a young age are common. Although replacement of ADAMTS13 can prevent morbidities and death, current regimens of plasma prophylaxis are insufficient. We identified 226 patients with hTTP in 96 reports published from 2001 through 2020. Age at diagnosis was reported for 202 patients; 117 were female and 85 were male. The difference was caused by diagnosis of 34 women during pregnancy, suggesting that many men and nulliparous women are not diagnosed. Eighty-three patients had severe jaundice at birth; hTTP was suspected and effectively treated in only 3 infants. Of the 217 patients who survived infancy, 73 (34%) had major morbidities defined as stroke, kidney injury, or cardiac injury that occurred at a median age of 21 years. Sixty-two patients had stroke; 13 strokes occurred in children age 10 years or younger. Of the 54 patients who survived their initial major morbidity and were subsequently observed, 37 (69%) had sustained or subsequent major morbidities. Of the 39 patients who were observed after age 40 years, 20 (51%) had experienced a major morbidity. Compared with an age- and sex-matched US population, probability of survival was lower at all ages beginning at birth. Prophylaxis was initiated in 45 patients with a major morbidity; in 11 (28%), a major morbidity recurred after prophylaxis had begun. Increased recognition of hTTP and more effective prophylaxis started at a younger age are required to improve health outcomes.

Thrombotic Thrombocytopenic Purpura Presentation in an Elderly Gentleman Following COVID Vaccine Circumstances

Thrombotic thrombocytopenic purpura (TTP) is a rare blood disorder that results in the formation of thrombi in the small blood vessels throughout the body. The two primary forms of TTP are acquired and familial forms. The acquired form usually presents in late childhood or adulthood. Almost 95% of the cases are due to an autoantibody directed against ADAMTS13, and the remaining 5% are due to drugs like ticlopidine, quinine, cyclosporine, gemcitabine, bevacizumab, and certain recreational drugs like ecstasy and cocaine. The familial forms present in infancy or early childhood, but sometimes they can present later in life. Management for acquired forms includes therapeutic plasma exchange and immunosuppressive agents. While for the hereditary forms, the mainstay of treatment is plasma infusion.

We present a case of an 80-year-old male with a known medical history of hypertension, type II diabetes mellitus, hyperlipidemia, gout, iron deficiency anemia, and Pfizer-BioNTech COVID-19 (coronavirus disease-19) vaccine administered two weeks before presentation to the ER for evaluation of generalized weakness and malaise. Laboratory findings showed severe anemia with hemoglobin of 4.8 g/dl, platelet count of 48 x 10^3/mcL, elevated lactate dehydrogenase (LDH), decreased haptoglobin, and peripheral smear showing schistocytes. The serum creatinine, total bilirubin, and troponin were elevated. All these findings were raising concern for presumptive diagnosis of TTP, which was confirmed with ADAMTS13 levels less than 10%. TTP was temporarily resolved in 10 days with plasma exchange therapy and high-dose corticosteroids.

It is difficult at this time to differentiate vaccine‐induced TTP from coincidental TTP presenting soon after vaccination. Further studies would be needed to understand better if this relationship between vaccination and TTP was coincidental or causal.

Best practices and recommendations for drug regimens and plasma exchange for immune thrombotic thrombocytopenic purpura

INTRODUCTION

Thrombotic thrombocytopenic purpura (TTP) is a life-threatening thrombotic microangiopathy characterized by microangiopathic hemolytic anemia, thrombocytopenia, and organ injury. TTP pathophysiology is based on a severe ADAMTS13 deficiency, and is a medical emergency with fatal outcome if appropriate treatment is not initiated promptly.

AREAS COVERED

Authors will review the best options currently available to minimize mortality, prevent relapses, and obtain the best clinical response in patients with immune TTP (iTTP). Available bibliography about iTTP treatment has been searched in Library's MEDLINE/PubMed database from January 1990 until April 2021.

EXPERT OPINION

The generalized use of plasma exchange marked a paradigm in the management of iTTP. In recent years, strenuous efforts have been done for a better understanding of the pathophysiology of this disease, improve diagnosis, optimize treatment, reduce mortality, and prevent recurrences. The administration of front-line rituximab and, more recently, the availability of caplacizumab, the first targeted therapy for iTTP, have been steps toward a further reduction in early mortality and for the prevention of relapses.

Thrombotic Thrombocytopenic Purpura: When Basic Science Meets Clinical Research

The therapeutic landscape of thrombotic thrombocytopenic purpura (TTP) is rapidly changing with the recent availability of new targeted therapies. This progressive shift from empiricism to pathophysiology-based treatments reflects an intensive interaction between the continuous findings in the field of basic science and an efficient collaborative clinical research and represents a convincing example of the strength of translational medicine. Despite the rarity of TTP, national and international efforts could circumvent this limitation and shed light on the epidemiology, clinical presentation, prognosis, and long-term outcome of this disease. Importantly, they also provided high-quality results and practice changing studies for the benefit of patients. We report here the most recent therapeutic findings that allowed progressively improving the prognostic of TTP, both at the acute phase and through long-term outcome.

Thrombotic Thrombocytopenic Purpura: Pathophysiology, Diagnosis, and Management

Thrombotic thrombocytopenic purpura (TTP) is a rare thrombotic microangiopathy characterized by microangiopathic hemolytic anemia, severe thrombocytopenia, and ischemic end organ injury due to microvascular platelet-rich thrombi. TTP results from a severe deficiency of the specific von Willebrand factor (VWF)-cleaving protease, ADAMTS13 (a disintegrin and metalloprotease with thrombospondin type 1 repeats, member 13). ADAMTS13 deficiency is most commonly acquired due to anti-ADAMTS13 autoantibodies. It can also be inherited in the congenital form as a result of biallelic mutations in the ADAMTS13 gene. In adults, the condition is most often immune-mediated (iTTP) whereas congenital TTP (cTTP) is often detected in childhood or during pregnancy. iTTP occurs more often in women and is potentially lethal without prompt recognition and treatment. Front-line therapy includes daily plasma exchange with fresh frozen plasma replacement and immunosuppression with corticosteroids. Immunosuppression targeting ADAMTS13 autoantibodies with the humanized anti-CD20 monoclonal antibody rituximab is frequently added to the initial therapy. If available, anti-VWF therapy with caplacizumab is also added to the front-line setting. While it is hypothesized that refractory TTP will be less common in the era of caplacizumab, in relapsed or refractory cases cyclosporine A, N-acetylcysteine, bortezomib, cyclophosphamide, vincristine, or splenectomy can be considered. Novel agents, such as recombinant ADAMTS13, are also currently under investigation and show promise for the treatment of TTP. Long-term follow-up after the acute episode is critical to monitor for relapse and to diagnose and manage chronic sequelae of this disease.

First reported case of congenital thrombotic thrombocytopenic purpura in Taiwan with novel mutation of ADAMTS13 gene

Congenital thrombotic thrombocytopenic purpura (cTTP) is a rare disease that is defined as biallelic mutations of ADAMTS13 causing persistent absence of ADAMTS13 activity. The confirmed diagnosis requires a genetic study, and cTTP has never been previously reported in Taiwan. Our patient was a 29-year-old Taiwanese woman who presented with severe hyperbilirubinemia at birth. She had severe thrombocytopenia and hemolytic anemia at the age of 1, and another acute TTP event at the age of 7 triggered by an upper airway infection. Regular plasma replacement was started at age 12 based on a presumptive diagnosis of cTTP. Clinical diagnosis of cTTP, with undetectable ADAMTS13 activity and absence of ADAMTS13 inhibitor, was confirmed at age 27. A genetic study showed a previously reported mutation c.1921G to A, inherited from her father, and a maternally inherited, novel mutation at exon 12, c.1435+1dupG, which results in a splicing site change and frame shift. Reports of cTTP from East Asia, except Japan, are scarce. Some prevalent ADAMTS13 mutations are also race or region specific. With this report, we hope to raise awareness among physicians in Taiwan, promote early, proper diagnosis of cTTP, and reveal the true prevalence of cTTP in the Taiwanese population.

Therapeutic plasma exchange in thrombotic thrombocytopenic purpura

Thrombotic thrombocytopenic purpura (TTP) is a life-threatening disease related to the formation of microvascular thrombosis and subsequent organ failure. The disease is accompanied with microangiopathic haemolytic anaemia, consumptive thrombocytopenia and lies on a severe deficiency in ADAMTS13, the von Willebrand factor-cleaving protease. In the acquired, immune-mediated form, this deficiency is due to the production of autoantibodies directed against the enzyme. Therapeutic plasma exchange has been used empirically for decades and still represents the cornerstone of TTP treatment. However, a better understanding of pathophysiological mechanisms underlying the disease has led these last years to the development of highly effective targeted therapies that might in the future restraint the use of therapeutic plasma exchange.

Thrombotic Thrombocytopenic Purpura: Beyond Empiricism and Plasma Exchange

For many years after its first description in 1924, thrombotic thrombocytopenic purpura was an intriguing puzzle for clinicians and researchers, not only for its unique pathology, perplexing changes in von Willebrand factor multimers, and high rate of rapid fatality but also for its dramatic response to plasma infusion or exchange. The discovery of ADAMTS13 (a disintegrin and metalloprotease with thrombospondin type 1 repeats member-13) and its deficiency in patients with thrombotic thrombocytopenic purpura, due to inhibitory autoantibodies or genetic mutations, provides a mechanistic scheme for understanding its pathogenesis. This new knowledge quickly led to the use of rituximab to promote its remission and prevent recurrence. Recombinant ADAMTS13 is also under development to replace plasma infusion as the therapy for hereditary thrombotic thrombocytopenic purpura. Recently, caplacizumab, a bivalent nanobody targeting the glycoprotein 1b binding epitope of von Willebrand factor A1 domain, was approved as an addition to the current regimen of plasma exchange and immunomodulation for adult patients of acquired thrombotic thrombocytopenic purpura. This review discusses how the new treatment may improve patient outcomes and its potential pitfalls.

Developments in the use of plasma exchange and adjunctive therapies to treat immune-mediated thrombotic thrombocytopenic purpura

Introduction: Immune-mediated thrombotic thrombocytopenic purpura (iTTP) is a life-threatening disease characterized by a severe functional deficit in the von-Willebrand cleaving protease ADAMTS13, due to autoantibody production. The once-dismal prognosis of the disease has been changed by the discovery of the dramatic efficiency of therapeutic plasma exchange (TPE). Areas covered: This review focuses on the history and recent developments in the use of TPE for iTTP with a special emphasis on the consequences for TPE practice of the recent introduction of new highly effective immunosuppressive strategies and anti-von Willebrand factor (vWF) therapies. Expert opinion: Although TPE still represents the cornerstone, emergency treatment of iTTP, their duration, and associated complications could be dramatically reduced in the future by the systematic addition of early immunosuppression using corticosteroids and rituximab as well as an anti-vWF therapy with caplacizumab.

When targeted therapies alleviate the burden of TPE: The example of immune-mediated TTP

Thrombotic thrombocytopenic purpura is a rare and severe disease that manifests as a thrombotic microangiopathy with severe thrombocytopenia and variable multiorgan failure. The disease relies on a severe deficiency in a disintegrin and metalloprotease with thrombospondin type-1 repeats, 13^th member (ADAMTS13), the von Willebrand factor (vWF) cleaving protease which can be either inherited (congenital TTP) or immune-mediated (iTTP). In iTTP, the therapeutic strategy has long relied on therapeutic plasma exchange alone which still represents the only way to deliver large amounts of ADAMTS13 without risking fluid overload. Yet, several therapeutic strategies have been developed in recent years and are about to transform the standard of care of iTTP. The immunosuppressive regimen now increasingly encompasses the administration of frontline rituximab to all patients. Moreover, the impressive results of the anti-vWF nanobody caplacizumab in phase 2 and 3 studies have recently prompted its approval by health authorities for the initial treatment of the disease. The increasing use of these highly effective targeted therapies should translate in a reduced need for therapeutic plasma exchange and an improvement in the prognosis of the disease. Nevertheless, and until the development of a recombinant ADAMTS13, this cornerstone therapy remains irreplaceable.

The remarkable diversity of thrombotic thrombocytopenic purpura: a perspective

Understanding the autoimmune etiology of acquired thrombotic thrombocytopenic purpura (TTP) has provided precision for the diagnosis and a rationale for immunosuppressive treatment. These advances have also allowed recognition of the remarkable clinical diversities of patients' initial presentations and their long-term outcomes. These diversities are illustrated by the stories of patients from the Oklahoma TTP Registry. The initial presentation of TTP may be the discovery of unexpected severe thrombocytopenia in a patient with minimal or no symptoms. The patient may remain asymptomatic throughout treatment or may die suddenly before treatment can be started. ADAMTS13 activity may be reported as normal in a patient with characteristic clinical features of TTP, or the unexpected report of ADAMTS13 deficiency in a patient with another established disorder may lead to the discovery of TTP. ADAMTS13 activity during clinical remission is unpredictable. ADAMTS13 activity may recover and remain normal, it may remain severely deficient for many years, or it may become normal only many years after recovery. Our treatment of initial episodes and management of patients after recovery and during remission continue to change. The addition of rituximab to the treatment of acute episodes and preemptive rituximab for patients with severe ADAMTS13 deficiency during remission are reported to prevent relapse. Because TTP is uncommon, there are few data to guide these changes. Therefore our patients' stories are profoundly influential. Their stories are the foundation of our experience, and our experience is the guide for our decisions.

Early versus late institution of plasma exchange therapy in pregnancy induced thrombotic microangiopathy and its effects on clinical outcomes-A case series

PURPOSE

To look for incidence of pregnancy associated TMA, clinical presentation and impact of early diagnosis and institution of plasma exchange on overall renal outcomes METHODS: -This is a retrospective study among all female patients who presented with acute kidney injury post pregnancy between October 2002 to April 2016 in department of nephrology in a tertiary care hospital in northern India and diagnosed as pregnancy induced TMA. The patient were assessed for duration of onset of renal failure to time of diagnosis of TMA, role of modality of treatment ie plasmpaharesis to outcome. These patients were assessed for complete, partial or no recovery in renal functions at 60 days after admission.

RESULTS

Patients whose time of onset of renal failure to a correct diagnosis of TMA was ≤15 days and age less than 30 years was also associated with good prognosis. The patients who received plasma exchange and that to within 72 h of admission had more chances of recovery.

CONCLUSIONS

Early diagnosis of disease and early institution of plasma exchange therapy improves renal outcomes in postpartum TMA.

Thrombotic thrombocytopenic purpura: pathogenesis, diagnosis and potential novel therapeutics

Thrombotic thrombocytopenic purpura (TTP), a potentially fatal clinical syndrome, is primarily caused by autoantibodies against the von Willebrand factor (VWF)-cleaving metalloprotease ADAMTS-13. In general, severe deficiency of plasma ADAMTS-13 activity (< 10 IU dL-1 ) with or without detectable inhibitory autoantibodies against ADAMTS-13 supports the diagnosis of TTP. A patient usually presents with thrombocytopenia and microangiopathic hemolytic anemia (i.e. schistocytes, elevated serum lactate dehydrogenase, decreased hemoglobin and haptoglobin) without other known etiologies that cause thrombotic microangiopathy (TMA). Normal to moderately reduced plasma ADAMTS-13 activity (> 10 IU dL-1 ) in a similar clinical context supports an alternative diagnosis such as atypical hemolytic uremic syndrome (aHUS) or other types of TMA. Prompt differentiation of TTP from other causes of TMA is crucial for the initiation of an appropriate therapy to reduce morbidity and mortality. Although plasma infusion is often sufficient for prophylaxis or treatment of hereditary TTP due to ADAMTS-13 mutations, daily therapeutic plasma exchange remains the initial treatment of choice for acquired TTP with demonstrable autoantibodies. Immunomodulatory therapies, including corticosteroids, rituximab, vincristine, cyclosporine, cyclophosphamide and splenectomy, etc., should be considered to eliminate autoantibodies for a sustained remission. Other emerging therapeutic modalities, including recombinant ADAMTS-13, adeno-associated virus (AAV) 8-mediated gene therapy, platelet-delivered ADAMTS-13, and antagonists targeting the interaction between platelet glycoprotein 1b and VWF are under investigation. This review highlights the recent progress in our understanding of the pathogenesis and diagnosis of, and current and potential novel therapies for, hereditary and acquired TTP.

Thrombotic Thrombocytopenic Purpura

Thrombotic thrombocytopenic purpura (TTP) is classically highlighted by a pentad of features: fever, hemolytic anemia, thrombocytopenia purpura, transient or permanent central nervous system signs, and renal disease. The antemortem diagnosis is reliant upon the multisystem clinical signs and symptoms in conjunction with severe hemolytic anemia and thrombocytopenia. Relapse is common within the first six months after initial presentation. Laboratory findings have been generally nonspecific per se, and antemortem tissue biopsy findings are frequently unrewarding. Recently, however, unusually large multimers of the Factor VIII:Ag molecule (von Willebrand protein) have been identified in the plasma of patients with TTP who have recovered from an acute attack. This observation is very important because it may lead to essential information on the nature of the inciting event in this devastating illness. The differential diagnosis includes several multisystem disease processes such as the hemolytic uremic syndrome, toxemia of pregnancy, systemic lupus erythematosus, subacute bacterial endocarditis, nonbacterial thrombotic endocarditis, immune thrombocytopenic purpura, and the postpartum renal failure syndrome. The hemolytic uremic syndrome, toxemia of pregnancy, and TTP may resemble each other, exhibit many overlapping features, and are probably related. The cause of TTP remains unknown; the overwhelming majority of cases occur in otherwise healthy people without any recognizable underlying illness. Since 1965 45 to 70% of patients survive, a significant improvement in contrast to the early 1900s when the mortality rate was greater than 90%. The most dramatic advance has been observed in therapeutics, namely the utilization of some mode of plasma therapy (either infusion alone or plasmapheresis followed by plasma infusion). Corticosteroids remain very important in the management of patients with TTP. Vincristine may be very helpful, but additional studies are needed. The efficacy of vinca alkaloids, chronic immunosuppressive therapy, and sple. nectomy remains undefined. At present there is very little, if any, evidence that antiplatelet agents, aspirin, and prostacyclin are beneficial to patients with TTP. Prompt diagnosis and vigorous aggressive therapy is critical for successful management of TTP patients.

Thrombotic microangiopathy: current knowledge and outcomes with plasma exchange

The classification of thrombotic microangiopathy has evolved and expanded due to treatment and mechanistic advances. The two basic clinical forms of thrombotic microangiopathy (excluding disseminated intravascular coagulation [DIC]), thrombotic thrombocytopenic purpura (TTP), and hemolytic uremic syndrome (HUS) encompass a wide range of primary and secondary forms. The advent of plasma therapy and the identification of an inhibitor to ADAMTS13 in the idiopathic or acute forms of TTP and its absence in diarrheal HUS have had a major impact on our current classification of thrombotic microangiopathy. In adults, the difficulty of differentiating TTP, which is much more common than HUS and the need for a speedy diagnosis to provide life-saving plasma therapy has resulted in the term TTP/HUS for adult forms of thrombotic microangiopathy that present with unexplained thrombocytopenia and microangiopathic hemolytic anemia without a DIC. In this adult population a primary idiopathic and hereditary form as well as eight known secondary categories or clinical forms of TTP/HUS have been identified. HUS also embraces a primary (atypical HUS) and secondary forms (majority, diarrheal HUS secondary to Escherichia coli 0157:H7). In children, who present with HUS with no preceding history of diarrhea, plasma therapy is also offered on an urgent basis and studies are carried out to determine if they are suffering an abnormality in complement activation that may require eculizumab therapy. The advent of plasma therapy in the treatment of thrombotic microangiopathy has led to a clearer understanding of the role of ADAMTS13, both short- and long-term outcomes and the need for future surveillance and intervention.

Recombinant ADAMTS13 normalizes von Willebrand factor-cleaving activity in plasma of acquired TTP patients by overriding inhibitory antibodies

BACKGROUND

Severe deficiency of the von Willebrand factor (VWF)-cleaving protease ADAMTS13 as observed in acquired thrombotic thrombocytopenic purpura (TTP) is caused by inhibitory and non-inhibitory autoantibodies directed against the protease. Current treatment with plasma exchange is considered to remove circulating antibodies and to concurrently replenish the deficient enzyme.

OBJECTIVES

To explore the use of recombinant ADAMTS13 (rADAMTS13) as a potential therapeutic agent in acquired TTP, we investigated its efficacy in normalizing VWF-cleaving activity in the presence of ADAMTS13 inhibitors.

METHODS

Thirty-six plasma samples from TTP patients were adjusted to predefined inhibitor titers, and recovery of ADAMTS13 activity was analyzed following supplementation with rADAMTS13.

RESULTS

We showed a linear relation between the inhibitor titer measured and effective rADAMTS13 concentration necessary for reconstitution of VWF-cleaving activity in the presence of neutralizing autoantibodies.

CONCLUSIONS

Our results support the further investigation of the potential therapeutic applicability of rADAMTS13 as an adjunctive therapy in acquired TTP.

Thrombotic microangiopathy in haematopoietic cell transplantation: an update

Allogeneic hematopoietic cell transplantation (HCT) represents a vital procedure for patients with various hematologic conditions. Despite advances in the field, HCT carries significant morbidity and mortality. A rare but potentially devastating complication is transplantation-associated thrombotic microangiopathy (TA-TMA). In contrast to idiopathic TTP, whose etiology is attributed to deficient activity of ADAMTS13, (a member of the A Disintegrin And Metalloprotease with Thrombospondin 1 repeats family of metalloproteases), patients with TA-TMA have > 5% ADAMTS13 activity. Pathophysiologic mechanisms associated with TA-TMA, include loss of endothelial cell integrity induced by intensive conditioning regimens, immunosuppressive therapy, irradiation, infections and graft-versus-host (GVHD) disease. The reported incidence of TA-TMA ranges from 0.5% to 75%, reflecting the difficulty of accurate diagnosis in these patients. Two different groups have proposed consensus definitions for TA-TMA, yet they fail to distinguish the primary syndrome from secondary causes such as infections or medication exposure. Despite treatment, mortality rate in TA-TMA ranges between 60% to 90%. The treatment strategies for TA-TMA remain challenging. Calcineurin inhibitors should be discontinued and replaced with alternative immunosuppressive agents. Daclizumab, a humanized monoclonal anti-CD25 antibody, has shown promising results in the treatment of TA-TMA. Rituximab or the addition of defibrotide, have been reported to induce remission in this patient population. In general, plasma exchange is not recommended.

Komplexe Gerinnungsstörungen

Die thrombotisch-thrombozytopenische Purpura (TTP) und das hämolytischurämische Syndrom (HUS) sind thrombotische Mikroangiopathien, gekennzeichnet durch eine Endothelzellschädigung mit nachfolgender Bildung von Thromben in der Mikrozirkulation mit intravasaler Hämolyse und Thrombozytopenie. Ischämische Organdysfunktionen im Gehirn, den Nieren und anderen Organen Prägen das klinische Bild. Während bei Erwachsenen das Auftreten einer neurologischen Symptomatik zur Diagnose TTP führt, wird bei Kindern mit dem Leitsymptom Nierenversagen die Diagnose HUS gestellt.

High versus standard dose methylprednisolone in the acute phase of idiopathic thrombotic thrombocytopenic purpura: a randomized study

Therapeutic plasma exchange (PE) is the accepted therapy for thrombotic thrombocytopenic purpura (TTP). Because not all patients achieve remission, other treatment modalities have been used in addition to PE, but no randomized clinical trial evaluated their efficacy. The aim of this multicentric study was to compare the effectiveness of standard- versus high-dose methylprednisolone as an adjunctive treatment to PE in the acute phase of TTP. Sixty patients with idiopathic TTP were randomized to receive methylprednisolone 1 mg/kg/die intravenous or 10 mg/kg/die for 3 days, thereafter, 2.5 mg/kg/die in addition to PE. Both dosages of steroids were well tolerated. At the end of induction therapy (day 23), the percentage of patients failing to achieve complete remission was significantly higher in the standard dose (16 of 30) than in the high-dose group (seven of 30). Also, the number of cases without a good response at day 9 and the number of deaths were higher in the standard-dose arm, but the differences did not reach the statistical significance. Results of present study indicate that the association of PE with high-dose instead of standard-dose steroids reduces the percentage of TTP patients that fail to achieve complete remission.

Adenoviral-mediated gene transfer restores plasma ADAMTS13 antigen and activity in ADAMTS13 knockout mice

ADAMTS13 is a plasma metalloprotease that regulates the size of the von Willebrand factor (VWF) multimers. Genetic or acquired deficiency of ADAMTS13 causes thrombotic thrombocytopenic purpura (TTP) in humans. Plasma infusion is the treatment of choice for patients with congenital ADAMTS13 deficiency. However, this practice exposes patients to the risk of infections, allergies and fluid volume overload. The search for alternative treatments is required. Here, we tested the ability of systemically administered adenovirus encoding human ADAMTS13 to restore the deficient protein in the circulation of Adamts13(-/-) mice. Injection of the adenovirus efficiently transduced the liver, kidney, lung, heart and spleen, resulting in the secretion of ADAMTS13 into plasma. A reduced area of thrombi was observed when blood from Ad-ADAMTS13-treated mice was perfused over a collagen-coated surface in a parallel plate flow chamber compared with blood of Ad-betaGal-treated controls. The secreted ADAMTS13 protein was functionally active even after 2 months from injection. The data provide the proof of principle for developing a novel therapy for the correction of ADAMTS13 deficiency in patients with hereditary TTP.

Successful treatment of hemolytic uremic syndrome and thrombotic thrombocytopenic purpura with fresh frozen plasma and plasma exchange

Four patients with hemolytic uremic syndrome (HUS) and seven with thrombotic thrombocytopenic purpura (TTP) were treated with infusions of fresh frozen plasma (FFP). In one patient with HUS and five patients with TTP this treatment was combined with plasma exchange (PE). The additional treatment varied; corticosteroids, antiplatelet drugs, heparin and blood exchange. All but one patient recovered completely in spite of severe illness with uremia, oliguria and/or cerebral symptoms during the acute phase. The results were surprisingly good in comparison with other published series. The success must in the first place be attributed to early diagnosis and to the infusions of FFP. PE seemed to potentiate the effect of FFP.

TTP/HUS: observational studies generate hypotheses that lead to randomized controlled trials

Thrombotic thrombocytopenic purpura (TTP)/hemolytic uremic syndrome (HUS) is a disease syndrome, and its history exemplifies how small observational studies lead to hypotheses that spawn randomized control trials (RCTs). Moschowitz's original case report coupled with the case findings of Bukowski and Byrne led to the RCT of Rock and the Canadian Apheresis Group that proved plasma exchange was superior to plasma infusion for the treatment of adults with TTP/HUS. Our single case report of continuous plasma exchange coupled with the observations about the pathogenic role of von Willebrand multimer protease of Tsai and Furlan strengthened by a 25-year observational study of plasma exchange treatment for TTP/HUS has led to a proposal to initiate a new RCT.