ADAMTS13 autoantibodies in patients with thrombotic microangiopathies and other immunomediated diseases

ADAMTS-13 conformation influences autoimmune recognition in immune thrombotic thrombocytopenic purpura

BACKGROUND

Patients with immune-mediated thrombotic thrombocytopenic purpura (iTTP) have anti-ADAMTS-13 immunoglobulin G (IgG) autoantibodies that enhance ADAMTS-13 clearance and/or inhibit its function. ADAMTS-13 normally circulates in a closed conformation, which is manifested by the interaction of the CUB domains with the central spacer domain. Disruption of the spacer-CUB interaction opens ADAMTS-13, which augments its proteolytic function but may also expose cryptic autoimmune epitopes that promote further autoantibody recognition.

OBJECTIVES

To explore differences in autoantibody binding to ADAMTS-13 in its closed or open conformations in patients with iTTP and to correlate these differences with disease-related parameters.

METHODS

We developed a novel assay to measure autoantibodies binding to closed and open ADAMTS-13. Autoantibody titer and IgG subclass binding to open or closed ADAMTS-13 were measured in 70 iTTP first presentation samples and correlated with clinical data, remission, and relapse.

RESULTS

In 70 patients with iTTP, the mean autoantibody titer against open ADAMTS-13 was, on average, approximately 2-fold greater than that against closed ADAMTS-13, suggesting that ADAMTS-13 opening increases epitope exposure and immune complex formation. Autoantibody titer against closed/open ADAMTS-13 and IgG subclass did not correlate with ADAMTS-13 antigen at presentation. Two patients with iTTP and persistent autoantibodies lost specificity for closed ADAMTS-13 in remission. Recognition of closed/open ADAMTS-13 and autoantibody IgG subclass between the first and second iTTP episodes were very similar.

CONCLUSION

ADAMTS-13 autoantibody binding is highly influenced by ADAMTS-13 conformation. Although this does not appear to modify the pathogenicity of autoantibodies, the autoantibody signature at relapse suggests that relapse represents re-emergence of the original autoimmune response rather than de novo presentation.

Plasmodium falciparum Malaria Presenting as a Thrombotic Thrombocytopenic Purpura (TTP) Mimic: A Case Report

Malaria can present with clinical manifestations overlapping with thrombotic thrombocytopenic purpura (TTP). We present the case of a 55-year-old female who presented with abdominal pain, fever, confusion, dehydration, and recent travel to Nigeria. Laboratory investigations were remarkable for low hemoglobin, decreased platelets, and elevated lactate. Suspicion for TTP occurred when the patient's platelet count and hemoglobin progressively decreased along with acute kidney injury and confusion. There was an elevated ADAMTS13 antibody level and mildly reduced ADAMTS13 activity suggesting possible TTP. However, Plasmodium falciparum was seen on peripheral blood smears. Treatment with artemether-lumefantrine was initiated which led to improvement in parasitemia, platelet count, and anemia. The similarity between malaria and TTP is mostly explained by thrombotic microangiopathic anemia (TMA) present in both diseases. Awareness of the common pathogenesis of TMA in both diseases and clinical judgment are pivotal in determining the timely initiation of appropriate treatment.

Medical consult: aHUS, TTP? How to distinguish and what to do

Immune thrombotic thrombocytopenic purpura (iTTP) caused by an autoantibody-mediated deficiency of ADAMTS13 and atypical hemolytic syndrome (aHUS) caused by alternative complement dysregulation are the most common primary thrombotic microangiopathies (TMAs). The evaluation of a patient with TMA is a medical emergency since it is critical to quickly distinguish iTTP and aHUS from other causes of TMA. Untreated iTTP is rapidly fatal, and delays in initiating complement inhibition in aHUS increase the risk of irreversible renal failure. An ADAMTS13 activity level of less than 10% is diagnostic of iTTP in the appropriate clinical setting. In settings where rapid-turnaround ADAMTS13 testing is not available, clinical features and clinical prediction tools are useful to identify patients who should receive emergent plasma exchange. We present an evidence-based approach to the initial (first 24 hours) diagnosis and management of iTTP and review the clinical and laboratory features that can be used to identify patients with aHUS who will benefit from early C5 blockade. We also discuss the potential use of complement blockade to improve outcomes in selected patients with secondary TMA.

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.

Reduced ADAMTS13 activity and high D-dimer levels are associated with thrombosis in patients with systemic lupus erythematosus

INTRODUCTION

Patients with systemic lupus erythematosus (SLE) have an increased risk of vascular thrombosis compared to the general population. Therefore, biomarkers for predicting the risk of thrombosis in patients with SLE are needed.

METHODS

In the present study, a total of 66 patients with SLE (22 with and 44 without a history of thrombosis) were enrolled. The cases with thrombosis and the controls without thrombosis were matched for age (± 5 years) and sex. We assessed ADAMTS13 activity, D-dimer levels, and antiphospholipid antibodies. Clinical manifestations, SLE disease activity, classical risk factors, and medical history were collected.

RESULTS

ADAMTS13 activity was significantly reduced, and D-dimer levels were significantly increased in patients with SLE with a history of thrombosis compared with those in patients without thrombosis. Receiver operating characteristic curve analysis revealed a good correlation between reduced ADAMTS13 activity and a history of thrombosis. Reduced ADAMTS13 activity was correlated with increased D-dimer levels only in the thrombotic group.

CONCLUSION

Reduced ADAMTS13 activity and high D-dimer levels are associated with thrombosis and may serve as prognostic markers for thrombosis in patients with SLE.

Anti-ADAMTS13 Autoantibodies: From Pathophysiology to Prognostic Impact-A Review for Clinicians

Thrombotic thrombocytopenic purpura (TTP) is a fatal disease in which platelet-rich microthrombi cause end-organ ischemia and damage. TTP is caused by markedly reduced ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) activity. ADAMTS13 autoantibodies (autoAbs) are the major cause of immune TTP (iTTP), determining ADAMTS13 deficiency. The pathophysiology of such autoAbs as well as their prognostic role are continuous objects of scientific studies in iTTP fields. This review aims to provide clinicians with the basic information and updates on autoAbs' structure and function, how they are typically detected in the laboratory and their prognostic implications. This information could be useful in clinical practice and contribute to future research implementations on this specific topic.

Autoantibodies enhance ADAMTS-13 clearance in patients with immune thrombotic thrombocytopenic purpura

BACKGROUND

Severe deficiency in ADAMTS-13 (<10%) and the loss of von Willebrand factor-cleaving function can precipitate microvascular thrombosis associated with thrombotic thrombocytopenic purpura (TTP). Patients with immune-mediated TTP (iTTP) have anti-ADAMTS-13 immunoglobulin G antibodies that inhibit ADAMTS-13 function and/or increase ADAMTS-13 clearance. Patients with iTTP are treated primarily by plasma exchange (PEX), often in combination with adjunct therapies that target either the von Willebrand factor-dependent microvascular thrombotic processes (caplacizumab) or the autoimmune components (steroids or rituximab) of the disease.

OBJECTIVES

To investigate the contributions of autoantibody-mediated ADAMTS-13 clearance and inhibition in patients with iTTP at presentation and through the course of the PEX therapy.

PATIENTS/METHODS

Anti-ADAMTS-13 immunoglobulin G antibodies, ADAMTS-13 antigen, and activity were measured before and after each PEX in 17 patients with iTTP and 20 acute TTP episodes.

RESULTS

At presentation, 14 out of 15 patients with iTTP had ADAMTS-13 antigen levels of <10%, suggesting a major contribution of ADAMTS-13 clearance to the deficiency state. After the first PEX, both ADAMTS-13 antigen and activity levels increased similarly, and the anti-ADAMTS-13 autoantibody titer decreased in all patients, revealing ADAMTS-13 inhibition to be a modest modifier of the ADAMTS-13 function in iTTP. Analysis of ADAMTS-13 antigen levels between consecutive PEX treatments revealed that the rate of ADAMTS-13 clearance in 9 out of 14 patients analyzed was 4- to 10-fold faster than the estimated normal rate of clearance.

CONCLUSION

These data reveal, both at presentation and during PEX treatment, that antibody-mediated clearance of ADAMTS-13 is the major pathogenic mechanism that causes ADAMTS-13 deficiency in iTTP. Understanding the kinetics of ADAMTS-13 clearance in iTTP may now enable further optimization of treatment of patients with iTTP.

Immune and Hereditary Thrombotic Thrombocytopenic Purpura: Can ADAMTS13 Deficiency Alone Explain the Different Clinical Phenotypes?

Thrombotic thrombocytopenic purpura (TTP) is a thrombotic microangiopathy caused by a hereditary or immune-mediated deficiency of the enzyme ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13). TTPs are caused by the following pathophysiological mechanisms: (1) the presence of inhibitory autoantibodies against ADAMTS13; and (2) hereditary mutations of the ADAMTS13 gene, which is present on chromosome 9. In both syndromes, TTP results from a severe deficiency of ADAMTS13, which is responsible for the impaired proteolytic processing of high-molecular-weight von Willebrand factor (HMW-VWF) multimers, which avidly interact with platelets and subendothelial collagen and promote tissue and multiorgan ischemia. Although the acute presentation of the occurring symptoms in acquired and hereditary TTPs is similar (microangiopathic hemolytic anemia, thrombocytopenia, and variable ischemic end-organ injury), their intensity, incidence, and precipitating factors are different, although, in both forms, a severe ADAMTS13 deficiency characterizes their physiopathology. This review is aimed at exploring the possible factors responsible for the different clinical and pathological features occurring in hereditary and immune-mediated TTPs.

Reversible skin microvascular hyporeactivity in patients with immune-mediated thrombocytopenic thrombotic purpura

BACKGROUND

Immune-mediated thrombotic thrombocytopenic purpura (iTTP) is a rare disease characterized by arteriolar and capillary microthrombosis precipitating organ failure. However, the contribution of endothelial dysfunction on impaired microvascular blood flow in iTTP patients has been poorly explored. This pilot observational study aimed to explore endothelial-mediated vasoreactivity in iTTP patients at admission and its changes after plasma exchange therapy (PE).

METHODS

We conducted a prospective observational study in patients (> 18-year old) admitted in ICU for iTTP. Using laser Doppler flowmetry and acetylcholine (Ach) iontophoresis in the forearm, we recorded the skin microvascular blood flow and the endothelium-mediated vasoreactivity at admission and after PE. Demographics, biological, clinical courses, and outcomes were also collected. As a control group, we used a previously published cohort of young diabetic patients after correction of ketoacidosis.

RESULTS

Eighteen confirmed iTTP patients and 34 controls were included in the study, mainly female (72%) aged 43 ± 16-year-old. At admission, 55% had neurological abnormalities, 50% cardiac issues and 27.8% an acute kidney injury. Median platelet count was 19 G/mL [10-37]. Baseline microvascular blood flow was decreased in iTTP patients when compared to controls (5.97 ± 4.5 vs. 10.1 ± 6.3 PU, P = 0.03), associated with markedly impaired endothelial-mediated skin microvascular reactivity (AUC: 9627 ± 8122 vs. 16,475 ± 11,738, P = 0.03). Microvascular reactivity improved after the first PE session (AUC: 9627 ± 8122 vs 16,558 ± 10,699, P = 0.007, respectively, baseline and post-PE1) and much more after the second session (26,431 ± 23,181, P = 0.04 post-PE1 vs post-PE2). Hemolysis biomarkers (LDH and bilirubin) negatively correlated with skin microvascular flow and vasoreactivity.

CONCLUSION

We highlighted a marked yet reversible skin endothelium-mediated microvascular hyporeactivity in iTTP patients that could participate in organ injury pathophysiology.

Secondary immune-mediated thrombotic thrombocytopenic purpura in idiopathic inflammatory myopathy: a case-based review

Immune-mediated thrombotic thrombocytopenic purpura (iTTP) is a potentially fatal acquired thrombotic microangiopathy syndrome that frequently develops in the context of infectious diseases or systemic autoimmune conditions including connective tissue diseases. We report the case of a 42-year-old female suffering from severe iTTP associated with anti-Jo-1 positive antisynthetase syndrome, which was successfully treated with combination therapy of intravenous immune globulin, rituximab and plasma exchange. Based on a systematic review of the literature, two additional cases of idiopathic inflammatory myopathy-associated iTTP (secondary iTTP) were identified. In conclusion, iTTP may be a rare complication of IIM that clinicians should consider in cases of marked thrombocytopenia. Further work-up of this finding should include a peripheral blood smear (schistocyte count) and ADAMTS13 activity. The concomitant manifestation of these autoimmune conditions may require intensive immunosuppressive therapy.

Frontiers in pathophysiology and management of thrombotic thrombocytopenic purpura

Thrombotic thrombocytopenic purpura (TTP) is a fatal disease in which platelet-rich microthrombi cause end-organ ischemia and damage. TTP is caused by markedly reduced ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) activity. Hereditary or congenital TTP (cTTP) is caused by ADAMTS13 gene mutations. In acquired or immune TTP (iTTP), ADAMTS13 activity is reduced by anti-ADAMTS13 autoantibodies. TTP is characterized by thrombocytopenia, hemolytic anemia, fever, renal dysfunction, and neuropsychiatric symptoms. Therapeutic plasma exchange (TPE) and immunosuppressive therapy are the mainstays of treatment. As untreated TTP has a high mortality rate, immediate initiation of TPE is recommended when TTP is suspected. Conventionally, corticosteroids have been used for immunosuppressive therapy. Current drug therapies include rituximab, an anti-CD20 antibody that is effective in newly diagnosed cases and refractory cases, as well as for relapse prevention, and caplacizumab, an anti- von Willebrand factor (VWF) nanobody that inhibits the binding of platelets to VWF and prevents microthrombi formation. Recombinant human ADAMTS13 is a promising treatment for cTTP. Although these therapeutic advances have improved the outcomes of TTP, early diagnosis and prompt initiation of appropriate therapy are necessary to achieve these outcomes.

An update on the pathogenesis and diagnosis of thrombotic thrombocytopenic purpura

INTRODUCTION

Severe ADAMTS13 deficiency defines thrombotic thrombocytopenic purpura (TTP). ADAMTS13 is responsible for VWF cleavage. In the absence of this enzyme, widespread thrombi formation occurs, causing microangiopathic anemia and thrombocytopenia and leading to ischemic organ injury. Understanding ADAMTS13 function is crucial to diagnose and manage TTP, both in the immune and hereditary forms.

AREAS COVERED

The role of ADAMTS13 in coagulation homeostasis and the consequences of its deficiency are detailed. Other factors that modulate the consequences of ADAMTS13 deficiency are explained, such as complement system activation, genetic predisposition, or the presence of an inflammatory status. Clinical suspicion of TTP is crucial to start prompt treatment and avoid mortality and sequelae. Available techniques to diagnose this deficiency and detect autoantibodies or gene mutations are presented, as they have become faster and more available in recent years.

EXPERT OPINION

A better knowledge of TTP pathophysiology is leading to an improvement in diagnosis and follow-up, as well as a customized treatment in patients with TTP. This scenario is necessary to define the role of new targeted therapies already available or coming soon and the need to better diagnose and monitor at the molecular level the evolution of the disease.

ADAMTS13 conformation and immunoprofiles in Japanese patients with immune-mediated thrombotic thrombocytopenic purpura

Immune-mediated thrombotic thrombocytopenic purpura (iTTP) is an ultrarare thrombotic disease caused by autoantibody-induced ADAMTS13 deficiency. Open ADAMST13 conformation, induced by autoantibodies, was identified as a novel biomarker for iTTP. Determining immunoprofiles in patients with iTTP has been shown to guide the development of novel targeted therapies. However, these studies were done in mainly Caucasian iTTP cohorts. To validate those findings across other ethnic cohorts, we investigated 195 acute TTP plasma samples from the Japanese iTTP registry. Seventy-six of the 195 samples had detectable ADAMTS13 antigen levels, of which 94.7% were shown to have an open ADAMTS13 conformation. A positive correlation was observed between ADAMTS13 inhibitor titers (a diagnostic parameter in Japan) and anti-ADAMTS13 immunoglobulin G autoantibody titers. Studying anti-M, anti-DT, anti-CS, anti-T2-T5, anti-T6-T8, anti-CUB1-2 autoantibodies and the corresponding immunoprofile showed that 73% of the patients had anti-CS autoantibodies and 25.8% had anti-M autoantibodies, with the latter being higher than in Caucasians. Stratifying patients according to their immunoprofiles revealed that the profile with only anti-CS autoantibodies was the most common immunoprofile similar to that in Caucasians (28.9%). Although this profile did not affect the 1-year TTP-related mortality rate, patients with autoantibodies against all 6 ADAMTS13 fragments had a higher risk for TTP-related death than other patients (P = .02). We here validated open ADAMTS13 as a novel biomarker for acute iTTP and determined the dominant immunoprofiling in the Japanese cohort, contributing to setting up the diagnosis and managing guidelines across different ethnic cohorts and developing ADAMTS13 variants that do not bind to the anti-CS autoantibodies.

A Rare Case of Severe Manifestation of COVID-19 Infection Presenting as Immune-Related Thrombotic Thrombocytopenic Purpura With Multiorgan Involvement Treated With Plasmapheresis, Steroids, Rituximab, and Caplacizumab

Thrombotic thrombocytopenic purpura (TTP) is a thrombotic microangiopathy (TMA) caused by decreased activity of a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 (ADAMTS13). Platelet-rich thrombi in small vessels lead to fragmentation of RBCs causing microangiopathic hemolytic anemia (MAHA). Therapeutic plasma exchange is life-saving and is the mainstay of the treatment of TTP. Higher dose IV steroids along with rituximab are used as an adjunct to plasma exchange.

Our case report describes a 26-year-old healthy male who presented with new onset seizures and encephalopathy. Blood work demonstrated anemia, severe thrombocytopenia, elevated lactate dehydrogenase, decreased haptoglobin, and elevated creatinine, and peripheral blood smear showed marked schistocytosis indicating MAHA. Plasma exchange and high-dose steroids were started on a presumptive diagnosis of TTP. ADAMTS13 activity was undetectable and ADAMTS13 inhibitor levels were elevated. Rituximab and caplacizumab were then added. Symptoms of encephalopathy improved by day five and platelet counts started improving by day nine. After several days of plasma exchange, he showed a “clinical response” with several weeks of active treatment. The association between coronavirus disease 2019 (COVID-19) infection and the severity of TTP with multiorgan failure is not well understood yet. Although we describe a successful multimodal approach to the management of TTP, which we believe is secondary to COVID-19 infection, further research is warranted to analyze and understand the pathophysiology by which COVID-19 infection causes TTP. It would help in establishing standardized therapy in the future.

Immune-Mediated Thrombotic Thrombocytopenic Purpura Following mRNA-Based COVID-19 Vaccine BNT162b2: Case Report and Mini-Review of the Literature

Introduction

An increasing number of case reports have associated vaccinations against coronavirus disease 2019 (COVID-19) with immune-mediated thrombotic thrombocytopenic purpura (iTTP), a very rare but potentially life-threatening thrombotic microangiopathy, which leads to ischemic organ dysfunction. Thrombus formation in iTTP is related to a severe deficiency of the specific von Willebrand-factor-cleaving protease ADAMTS13 due to ADAMTS13 autoantibodies.

Methods

We present a case of iTTP following exposure to the mRNA-based COVID-19 vaccine BNT162b2 (Comirnaty^®, Pfizer-BioNTech). In addition, we review previously reported cases in the literature and assess current evidence.

Results

Apart from our case, twenty cases of iTTP occurring after COVID-19 vaccination had been published until the end of November 2021. There were 11 male and 10 female cases; their median age at diagnosis was 50 years (range 14–84 years). Five patients (24%) had a preexisting history of iTTP. Recombinant adenoviral vector-based vaccines were involved in 19%, mRNA-based vaccines in 81%. The median onset of symptoms after vaccination was 12 days (range 5–37), with 20 cases presenting within 30 days. Treatment included therapeutic plasma exchange in all patients. Additional rituximab, caplacizumab, or both these treatments were given in 43% (9/21), 14% (3/21), and 24% (5/21) of cases, respectively. One patient died, despite a prolonged clinical course in one patient, all surviving patients were in clinical remission at the end of the observational period.

Conclusion

Clinical features of iTTP following COVID-19 vaccination were in line with those of pre-pandemic iTTP. When timely initiated, an excellent response to standard treatment was seen in all cases. ADAMTS13 activity should be determined pre-vaccination in patients with a history of a previous iTTP episode. None of the reported cases met the WHO criteria for assessing an adverse event following immunization (AEFI) as a consistent causal association to immunization. Further surveillance of safety data and additional case-based assessment are needed.

Pregnancy-associated thrombotic thrombocytopenic purpura complicated by Sjögren's syndrome and non-neutralising antibodies to ADAMTS13: a case report

Background

Thrombotic thrombocytopenic purpura (TTP) is a severe and life-threatening disease. Given its heterogeneous clinical presentation, the phenotype of TTP during pregnancy and its management have not been well documented.

Case presentation

We report here a 25-year-old woman, G1P0 at 36 weeks gestation, who developed severe thrombocytopenia and anemia. She was performed an emergent caesarean section 1 day after admission because of multiple organ failure. As ADAMTS 13 enzyme activity of the patient was 0% and antibodies were identified by enzyme-linked immunosorbent assay, she was diagnosed as acquired thrombotic thrombocytopenic purpura (aTTP). Furthermore, asymptomatic primary Sjögren’s syndrome was incidentally diagnosed on screening. After treatment with rituximab in addition to PEX and steroids, the activity of the ADAMTS 13 enzyme increased significantly from 0 to 100%.

Conclusions

To the best of our knowledge, this is the first case report of concomitant TTP and asymptomatic Sjögren’s syndrome in a pregnant woman. It highlights the association between pregnancy, autoimmune disease, and TTP. It also emphasizes the importance of an enzyme-linked immunosorbent assay in the diagnosis and rituximab in the treatment of patients with acquired TTP.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12884-021-04167-9.

Predictors of relapse and preventative strategies in immune thrombotic thrombocytopenic purpura

INTRODUCTION

Immune-mediated thrombotic thrombocytopenic purpura (iTTP) is a rare autoimmune blood disorder, which presents with microangiopathic hemolytic anemia, thrombocytopenia, and microvascular thrombosis and is caused by severe deficiency of ADAMTS13. iTTP may result in both acute and chronic complications and is rapidly fatal without expedient treatment. Life-time risk of relapse is approximately 40%.

AREAS COVERED

A number of predictors of relapse has been described in the literature. The most well-studied predictor of relapse is persistent ADAMTS13 deficiency; however, it is not a perfect marker. Relapse can be prevented by treatment with immunosuppressive medications, with rituximab being the most studied.

EXPERT OPINION

Patients who recover from iTTP should be regularly assessed, including with ADAMTS13 activity testing. The optimal frequency of assessments has not been established, but every 3 months is recommended. Considering the potential for significant organ damage and mortality associated with iTTP relapse, patients in remission and with persistent ADAMTS13 activity of 10-20% should be prophylactically treated with immunosuppression. Additional markers to precisely identify patients at higher risk of relapse are needed.

Evaluation and Management of Thrombotic Thrombocytopenic Purpura in the Emergency Department

BACKGROUND

Thrombotic thrombocytopenic purpura (TTP) is a dangerous condition that can be misdiagnosed in the emergency department.

OBJECTIVE

The purpose of this narrative review article is to provide a summary of the background, pathophysiology, diagnosis, and management of TTP, with a focus on emergency clinicians.

DISCUSSION

TTP is a disorder with microangiopathic hemolytic anemia, severe thrombocytopenia, and multiorgan ischemic injury. It may be acquired or hereditary, and is caused by a reduced amount or function of a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 (ADAMTS13), which is an enzyme involved in cleaving von Willebrand factor. The classic presentation of TTP includes fever, neurologic abnormalities, thrombocytopenia with purpura, microangiopathic hemolytic anemia, and acute renal injury. However, < 7% of cases have all of these findings present. Testing should include a complete blood count, complete metabolic panel, blood smear, coagulation panel, fibrinogen, D-dimer, lactate dehydrogenase, ADAMTS13 level, troponin, human immunodeficiency virus assessment, urinalysis, pregnancy test as appropriate, and electrocardiogram. Management includes hematology consultation if available, plasma exchange and corticosteroids, and treatment of end-organ complications. All patients require admission for treatment and close monitoring.

CONCLUSION

TTP is a potentially dangerous medical condition requiring rapid diagnosis and management. It is essential for emergency clinicians to know how to diagnose and treat this disorder.

ADAMTS13 testing update: Focus on laboratory aspects of difficult thrombotic thrombocytopenic purpura diagnoses and effects of new therapies

TTP is a life-threatening disorder diagnosed using a combination of clinical information and laboratory results. ADAMTS13 activity and antibody testing represent a major advance in the field, but results can sometimes be difficult to interpret due to technical aspects of the tests and characteristics of the causative antibodies in acquired TTP. Genetic testing for ADAMTS13 mutations is also now available to assist with the diagnosis of inherited TTP. This review will focus on ADAMTS13 testing and will highlight patient and laboratory aspects that can lead to diagnostic difficulty. The effects of TTP therapies on test results will also be discussed.

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 Microangiopathy Associated with Macrophage Activation Syndrome: A Multinational Study of 23 Patients

OBJECTIVE

To describe the clinical characteristics, treatment, and outcomes of a multinational cohort of patients with macrophage activation syndrome (MAS) and thrombotic microangiopathy (TMA).

STUDY DESIGN

International pediatric rheumatologists were asked to collect retrospectively the data of patients with the co-occurrence of MAS and TMA. Clinical and laboratory features of patients with systemic juvenile idiopathic arthritis (sJIA)-associated MAS and TMA were compared with those of an historical cohort of patients with sJIA and MAS.

RESULTS

Twenty-three patients with MAS and TMA were enrolled: 17 had sJIA, 2 systemic lupus erythematosus, 1 juvenile dermatomyositis, 1 mixed connective tissue disease, and 2 undifferentiated connective tissue disease. Compared with the historical cohort of MAS, patients with sJIA with coexistent MAS and TMA had higher frequencies of renal failure and neurologic involvement, hemorrhage, jaundice, and respiratory symptoms, as well as more severe anemia and thrombocytopenia, higher levels of alanine aminotransferase, lactate dehydrogenase, bilirubin and D-dimer, and lower levels of albumin and fibrinogen. They also required admission to the intensive care unit more frequently. Among patients tested, complement abnormalities and reduced ADAMTS13 activity were observed in 64.3% and 44.4% of cases, respectively. All patients received glucocorticoids. Treatment for TMA included plasma-exchange, eculizumab, and rituximab.

CONCLUSIONS

The possible coexistence of MAS and TMA in rheumatic diseases may be underrecognized. This association should be considered in patients with MAS who develop disproportionate anemia, thrombocytopenia, and lactate dehydrogenase increase, or have multiorgan failure.

Multiple thrombosis associated with Cytomegalovirus enterocolitis in an immunocompetent patient: a case report

BACKGROUND

Cytomegalovirus (CMV) is reported to have thrombogenic characteristics that activate factor X in vitro and stimulate the production of factor VIII and von Willebrand factor (vWF). Thrombosis associated with CMV infection is prevalent among immunocompromised patients and predominantly presents as a solitary large thrombus in the deep vein, pulmonary artery, splanchnic arteriovenous ducts, or other similar sites. Multiple thrombi, however, are rarely observed in such cases. Here, we report about an immunocompetent man with multiple microthrombi associated with CMV infection.

CASE PRESENTATION

A 72-year-old Japanese man who complained of abdominal pain was hospitalized with multiple colonic stenosis. He was later diagnosed with CMV enterocolitis and treated with ganciclover from Day 27 post-admission. During hospitalization, the patient developed thrombi in his fingers. He was initially treated with anticoagulant therapy (rivaroxaban); however, the therapy was discontinued owing to a prolonged activated thromboplastin time and an elevated international normalized ratio of prothrombin time. Instead, vitamin K and fresh-frozen plasma were administered. Nevertheless, his coagulation profile remained abnormal. Eventually, he developed colonic perforation and had to undergo emergency surgery. An intraoperative specimen showed several microthrombi in the middle and small arteriovenous ducts of his small and large intestines. The patient's coagulopathy improved preoperatively, and his overall condition improved postoperatively. Since the activation of ADAMTS13 was reduced remarkably, the thrombotic tendency was determined to be a thrombotic microangiopathy-like condition owing to increased vWF. We could not attribute the coagulopathy to any other cause except CMV infection; therefore, we concluded that this was a case of multiple thrombosis associated with CMV.

CONCLUSIONS

We present an extremely rare case of a patient with multiple thrombotic microangiopathy-like microthrombosis caused by CMV infection. Our findings suggest that CMV infection may be considered as a differential diagnosis for immunocompetent individuals who present with thrombosis of unspecified cause.

Hematologic Findings in Pregnancy: A Guide for the Internist

Hematologic changes in pregnancy are common and can potentially lead to maternal and fetal morbidity. Here, we present various hematologic manifestations seen in pregnant women. Iron deficiency anemia (IDA) is the most common cause of anemia in pregnancy. Physiologically, the state of pregnancy results in increased iron demand. Iron deficiency is important to diagnose and treat early for better maternal and fetal outcomes. An algorithmic approach is used for the repletion of iron storage, starting with oral elemental iron daily and escalating to intravenous iron if necessary. Folate and cobalamin are necessary elements for deoxyribonucleic acid (DNA) synthesis, fetal growth, and maternal tissue development, and deficiency in these elements can be a cause for anemia in pregnancy. Thrombocytopenia is currently the second most common hematologic condition in pregnancy after anemia. There is a wide range of etiology for thrombocytopenia in pregnancy from benign to life-threatening causes that require prompt diagnosis and treatment. These conditions include gestational thrombocytopenia, thrombotic thrombocytopenic purpura, pregnancy-associated atypical hemolytic-uremic syndrome, and immune thrombocytopenia. Acquired bleeding disorders that can cause major complications in pregnancy include von Willebrand disease (vWD) and coagulation factor deficiencies. Women with vWD are at increased risk of pregnancy bleeding and postpartum hemorrhage. Pregnancy can also produce a physiologic hypercoagulable state, leading to life-threatening conditions like thromboembolism. Diagnosis, treatment options, and guidelines for the management of these conditions will be explored in this review.

Double positivity of anti-β2-glycoprotein I domain I and anti-phosphatidylserine/prothrombin antibodies enhances both thrombosis and positivity of anti-ADAMTS13 antibody

Although a few antiphospholipid syndrome (APS) occurs with acquired thrombotic thrombocytopenic purpura (TTP), the relationship between antiphospholipid antibodies (aPL) and anti-ADAMTS13 (anti-a disintegrin and metalloprotease with thrombospondin type 1 motif, member 13) antibody remains uncertain. We investigated the relationship between high-risk thrombotic aPL and anti-ADAMTS13 antibody. Two hundred and thirty-seven patients with positive lupus anticoagulant and/or anticardiolipin antibody were included. Anti-β₂GPI (anti-β₂-glycoprotein I), anti-β₂GPIdI (anti-β2-glycoprotein I domain I), anti-PS/PT (anti-phosphatidylserine and prothrombin), ADAMTS13 activity, and anti-ADAMTS13 antibody were measured. Double positivity of anti-β₂GPI and anti-PS/PT increased thrombotic risk more than three-fold and showed increased positivity of anti-ADAMTS13 antibody in comparison with the double negative group. Double positivity of anti-β₂GPIdI and anti-PS/PT presented both effects even more. In the linear regression analysis, double positivity of anti-β₂GPI and anti-PS/PT independently affected the anti-ADAMTS13 antibody level (β = 1.982, P = 0.042). Our results revealed that double positivity of anti-β₂GPI or anti-β₂GPIdI and anti-PS/PT increased not only thrombotic risk but also the positivity of anti-ADAMTS13 antibody, especially indicating anti-β₂GPIdI showed a higher synergistic effect with anti-PS/PT. We suggest a possible association of anti-ADAMTS13 antibody with a high thrombotic risk of APS. Double positivity of anti-β₂GPI (anti-β₂-glycoprotein I) and anti-PS/PT (anti-phosphatidylserine and prothrombin) antibodies enhanced not only thrombotic risk but also positivity of anti-ADAMTS13 (anti-a disintegrin and metalloprotease with thrombospondin type 1 motif, member 13) antibody. Furthermore, double positivity of anti-β₂GPIdI (anti-β2-glycoprotein I domain I) combined with anti-PS/PT even more elevated both thrombosis and positivity of anti-ADAMTS13 antibody. Double positivity of β₂GPI and anti-PS/PT was found as an independently significant contributing factor to anti-ADAMTS13 antibody level. We suggest the association between anti-ADAMTS13 antibody and the pathophysiology of antiphospholipid syndrome, which should be further evaluated.

Continuous plasma exchange with dialysis for thrombotic microangiopathy in intensive care unit: Retrospective observational study

Continuous plasma exchange with dialysis is a novel method of blood purification and is a modification of the plasma exchange. Technically, this process suggests a reduction in adverse events, cost-effectiveness, and compatibility with hemodynamic instability. The therapeutic effect of plasma exchange on thrombotic microangiopathies has been established. We present three clinical cases in the intensive care unit that illustrate continuous plasma exchange with dialysis as a flexible blood purification therapy for critically ill patients; a radical treatment, thrombotic microangiopathies; supportive therapy, multiple organ failure; and fluid balance regulator. The retrospective analysis of 13 continuous plasma exchange with dialysis sessions showed that the platelet count increased significantly (p = 0.0096) after its administration. The total protein, albumin, fibrinogen, or calcium did not decrease significantly after continuous plasma exchange with dialysis, suggesting therapeutic efficacy and fewer adverse events. A prospective study on thrombotic microangiopathies for continuous plasma exchange with dialysis is currently underway.

Post-cardiac surgery thrombotic thrombocytopenic purpura: presence of anti-ADAMTS13 autoantibodies at preoperative baseline

Thrombotic thrombocytopenic purpura (TTP) rarely complicates acute inflammatory conditions such as surgery, including post-cardiac surgery. Review of 32 previously-reported cases of post-cardiac surgery TTP indicates that this disorder often occurs as early as 2-3 days following surgery, which seems too soon to implicate new formation of anti-ADAMTS13 autoantibodies as a consequence of surgery itself. We diagnosed post-cardiac surgery TTP in a 60-year-old female that began approximately 3 days post-coronary artery bypass surgery in which anti-ADAMTS13 autoantibodies were implicated. We therefore investigated whether anti-ADAMTS13 autoantibodies were also present in a preoperative blood sample. Inhibitory (neutralizing) anti-ADAMTS13 autoantibodies were detectable in the preoperative blood sample, suggesting that the role of surgery in precipitating TTP might be due to effects such as abrupt increase in postoperative von Willebrand factor levels and associated proinflammatory factors, rather than effects of surgery itself leading to the formation of de novo anti-ADAMTS13 autoantibodies.

Identification of a novel genetic locus associated with immune mediated thrombotic thrombocytopenic purpura

Immune thrombotic thrombocytopenic purpura (iTTP) is an ultra-rare, life-threatening disorder, mediated through severe ADAMTS13 deficiency causing multi-system micro-thrombi formation, and has specific human leukocyte antigen associations. We undertook a large genome-wide association study to investigate additional genetically distinct associations in iTTP. We compared two iTTP patient cohorts with controls, following standardized genome-wide quality control procedures for single-nucleotide polymorphisms and imputed HLA types. Associations were functionally investigated using expression quantitative trait loci (eQTL), and motif binding prediction software. Independent associations consistent with previous findings in iTTP were detected at the HLA locus and in addition a novel association was detected on chromosome 3 (rs9884090, P=5.22x10^-10, odds ratio 0.40) in the UK discovery cohort. Meta-analysis, including the French replication cohort, strengthened the associations. The haploblock containing rs9884090 is associated with reduced protein O-glycosyltransferase 1 (POGLUT1) expression (eQTL P<0.05), and functional annotation suggested a potential causative variant (rs71767581). This work implicates POGLUT1 in iTTP pathophysiology and suggests altered post-translational modification of its targets may influence disease susceptibility.

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.

Immunogenic hotspots in the spacer domain of ADAMTS13 in immune-mediated thrombotic thrombocytopenic purpura

BACKGROUND

Immune-mediated thrombotic thrombocytopenic purpura (iTTP) is caused by anti-ADAMTS13 autoantibodies inducing a severe deficiency of ADAMTS13. Epitope mapping studies on samples obtained during acute iTTP episodes have shown that the iTTP immune response is polyclonal, with almost all patients having autoantibodies targeting the spacer domain of ADAMTS13.

OBJECTIVES

To identify the immunogenic hotspots in the spacer domain of ADAMTS13.

PATIENTS/METHODS

A library of 11 full-length ADAMTS13 spacer hybrids was created in which amino acid regions of the spacer domain of ADAMTS13 were exchanged by the corresponding region of the spacer domain of ADAMTS1. Next, the full-length ADAMTS13 spacer hybrids were used in enzyme-linked immunosorbent assay to epitope map anti-spacer autoantibodies in 138 samples from acute and remission iTTP patients.

RESULTS

Sixteen different anti-spacer autoantibody profiles were identified with a similar distribution in acute and remission patients. There was no association between the anti-spacer autoantibody profiles and disease severity. Almost all iTTP samples contained anti-spacer autoantibodies against the following three regions: amino acid residues 588-592, 602-610, and 657-666 (hybrids E, G, and M). Between 31% and 57% of the samples had anti-spacer autoantibodies against amino acid regions 572-579, 629-638, 667-676 (hybrids C, J, and N). In contrast, none of the samples had anti-spacer autoantibodies against amino acid regions 556-563, 564-571, 649-656, and 677-685 (hybrids A, B, L, and O).

CONCLUSION

We identified three hotspot regions (amino acid regions 588-592, 602-610, and 657-666) in the spacer domain of ADAMTS13 that are targeted by anti-spacer autoantibodies found in a large cohort of iTTP patients.

ADAMTS13 and von Willebrand factor assessment in steady state and acute vaso-occlusive crisis of sickle cell disease

BACKGROUND

Sickle cell disease (SCD) is characterized by vaso-occlusive crisis (VOC), acute chest syndrome (ACS) and multiorgan failure (MOF) complicated by thrombosis. Von Willebrand factor (VWF) is a strong marker of SCD-related endothelial injury.

OBJECTIVES

To decipher the role of VWF and its specific-cleaving metalloprotease, ADAMTS13, in the vaso-occlusive and thrombotic process of SCD.

PATIENTS/METHODS

We investigated the VWF antigen (Ag), ADAMTS13 activity, ADAMTS13 Ag and ADAMTS13 IgGs in a cohort of 65 patients with SCD prospectively enrolled in a 20-month period from three centers. Patients were divided into two groups: an asymptomatic group (n = 30) with treated or untreated SCD at steady state, and a VOC/ACS group (n = 35) with SCD with VOC/ACS requiring either medical management or intensive care management for MOF.

RESULTS AND CONCLUSIONS

VWF:Ag levels were increased (median, 167 IU/dL; interquartile range [IQR], 124 - 279), especially in patients with VOC SCD (227 IU/dL; IQR, 134-305; P = .04), and positively correlated with inflammatory markers (P < .02). Median ADAMTS13 activity was normal (70 IU/dL; IQR, 60-80), but 7 patients exhibited a partial deficiency between 25 and 45 IU/dL. ADAMTS13 activity/VWF:Ag ratio, however, did not change during VOC. Median ADAMTS13:Ag was slightly decreased (611 ng/mL; IQR, 504-703) with no significant difference between groups. Surprisingly, ADAMTS13 IgGs were detected in 33 (51%) of our patients. We conclude that, in SCD, VWF:Ag and nonrelevant ADAMTS13 IgGs may reflect the severity of the inflammatory vasculopathy enhancing vaso-occlusive and thrombotic complications.

Optimization of the detection of inhibitory autoantibodies against the VWF-cleaving protease ADAMTS13 with an automated chemiluminescent ADAMTS13 activity immunoassay

INTRODUCTION

Acquired thrombotic thrombocytopenic purpura is a rare disease associated with the production of autoantibodies against the VWF-cleaving protease ADAMTS13. The detection of these antibodies is made difficult by the instability of ADAMTS13 in citrated plasma and the time-consuming ADAMTS13 assays. The aim of our study was to evaluate the optimal conditions for detecting anti-ADAMTS13 inhibitory antibodies with the novel automated chemiluminescent immunoassay HemosIL^R AcuStar ADAMTS13 Activity assay.

METHODS

The parallelism between the AcuStar ADAMTS13 calibration curve and ADAMTS13 concentrations in serially diluted citrated plasma was evaluated after 2 hours incubation at 25°C, 37°C, or 37°C after addition of Ca²⁺ to preserve the activity of the metalloprotease. Using Bethesda assays based on the 3 incubation procedures and the HemosIL^R AcuStar ADAMTS13 Activity assay, the inhibitor titers were determined in patients' samples with ADAMTS13 antibodies and compared with those determined using the Technozym^R ADAMTS13 activity ELISA.

RESULTS

The criterion of parallelism was respected for the 3 incubation methods over the range of ADAMTS13 concentrations relevant for the detection of ADAMTS13 inhibitor antibodies in a Bethesda assay. In agreement with this observation, all the incubation methods permitted the accurate detection and quantification of inhibitory anti-ADAMTS13 antibodies in the samples from patients with acquired thrombotic thrombocytopenic purpura.

CONCLUSION

Incubation of plasma samples with normal plasma at 25°C, 37°C, or 37°C after addition of Ca²⁺ can be used in a Bethesda assay for quantifying the inhibitory activity of antibodies interfering with ADAMTS13 in the chemiluminescent HemosIL^R AcuStar ADAMTS13 Activity assay.

Assessment and Monitoring of Patients with Immune-Mediated Thrombotic Thrombocytopenic Purpura (iTTP): Strategies to Improve Outcomes

Background

Acquired or immune-mediated TTP (iTTP) is a life-threatening thrombotic microangiopathy, characterized by the presence of microangiopathic hemolytic anemia and severe thrombocytopenia, and a variable degree of ischemic organ damage, related to a severe deficiency of ADAMTS13, which is a serine metalloprotease necessary for cleavage of large vWF multimers. There has been a dramatic decrease in mortality rates with the recognition of the pathophysiology of iTTP over the years. Although therapeutic plasma exchange (TPE) together with corticosteroids are the backbone of the upfront treatment of patients with iTTP with successful outcomes, patients may remain refractory and/or relapse following an initial response to this treatment.

Methods

We performed a review regarding the pathogenesis, diagnosis, treatment strategies, monitoring, and prognosis of iTTP.

Results

There are several new treatment strategies, which can be used among these patients, helping in improving outcomes of iTTP. Rituximab has been shown to be a safe and effective adjunct to TPE, especially in patients with refractory and/or relapse as well as it is increasingly used preemptively to prevent exacerbation or recurrence. Recently, caplacizumab, a nanobody targeting vWF, was approved as an addition to the current regimen of TPE and immunomodulation for patients of iTTP.

Conclusion

Specific predictors of relapse in patients in remission can be relevant for an optimal patient management. Different models including ADAMTS13 biomarkers can provide a new screening strategy to identify patients who may predict outcomes and the risk of relapse, benefit from preemptive therapy prior to relapse.

[The experience of using the Russian biosimilar of the original drug eculizumab for the treatment of patients with atypical hemolytic-uremic syndrome]

Atypical hemolytic-uremic syndrome (aHUS) is a chronic systemic disease of a genetic nature, which is based on uncontrolled activation of the alternative complement pathway, leading to generalized thrombosis in the vessels of the microvasculature (complement-mediated thrombotic microangiopathy). To date, therapy with eculizumab is the most effective and pathogenetically substantiated method of treating patients with ASH. Using the example of three clinical cases of patients with a verified diagnosis of aHUS, the high efficiency and safety of the worlds first bioanalogue of eculizumab in the treatment of adult patients with aHUS (complement-mediated thrombotic microangiopathy) was demonstrated.

Managing pregnancy-associated clinical emergencies in systemic lupus erythematosus: a case-based approach

Introduction: Systemic lupus erythematosus (SLE)-related thrombocytopenia during pregnancy and the postpartum period have been associated with adverse pregnancy outcomes and perinatal complications. In this case report, we present two SLE patients with thrombocytopenia emergencies secondary to HELLP (hemolysis, elevated liver enzymes, and low platelets) syndrome and thrombotic thrombocytopenic purpura (TTP).Areas covered: The first case involved a 26-year-old woman, G1P0 at 26 weeks gestation (GA), with high-titer antiphospholipid antibodies (aPL) (positive lupus anticoagulant, anti-beta 2 glycoprotein-1 (aβ2GP1), anti-cardiolipin) and non-criteria aPL to phosphatidylserine/prothrombin complex and anti-domain 1 β2GP1. This case highlights the risks associated with aPL in pregnancy, considers management issues relating to anticoagulation during pregnancy and highlights the importance of maintaining a high index of suspicion for diagnosis of HELLP in SLE patients. The second case was a 36-year-old female, G3P2 at 32 weeks GA, with class III lupus nephritis (LN) who developed severe pre-eclampsia, which included mild thrombocytopenia. This case illustrates the challenges in identifying and differentiating between three pregnancy emergencies that can be seen in SLE patients (pre-eclampsia, LN, and TTP) and presents the management of TTP in peripartum SLE.Expert opinion: These two cases remind us of the importance of timely diagnosis and management of thrombocytopenia in this 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.

Synergistic effects of ADAMTS13 deficiency and complement activation in pathogenesis of thrombotic microangiopathy

Severe deficiency of plasma ADAMTS13 activity is the primary cause of thrombotic thrombocytopenic purpura (TTP) whereas overwhelming activation of complement via an alternative pathway results in atypical hemolytic uremic syndrome (aHUS), the prototypes of thrombotic microangiopathy (TMA). However, clinical and pathogenic distinctions between TTP and aHUS are often quite challenging. Clinical reports have suggested that complement activation may play a role in the development of TTP, which is caused by severe deficiency of plasma ADAMTS13 activity. However, the experimental evidence to support this hypothesis is still lacking. Here, we show that mice with either Adamts13 -/- or a heterozygous mutation of complement factor H (cfh) at amino acid residue of 1206 (ie, cfh W/R ) alone remain asymptomatic despite the presence of occasional microvascular thrombi in various organ tissues. However, mice carrying both Adamts13 -/- and cfh W/R exhibit thrombocytopenia, low haptoglobin, increased fragmentation of erythrocytes in peripheral blood smear, increased plasma levels of lactate dehydrogenase activity, blood urea nitrogen, and creatinine, as well as an increased mortality rate, consistent with the development of TMA. Moreover, mice with a homozygous mutation of cfh (ie, cfh R/R ) with or without Adamts13 -/- developed severe TMA. The mortality rate in mice with Adamts13 -/- cfh R/R was significantly higher than that in mice with cfh R/R alone. Histological and immunohistochemical analyses demonstrated the presence of disseminated platelet-rich thrombi in terminal arterioles and capillaries of major organ tissues in these mice that were either euthanized or died. Together, our results support a synergistic effect of severe ADAMTS13 deficiency and complement activation in pathogenesis of TMA in mice.

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.

Thrombotic Thrombocytopenic Purpura Following Aortic Valve Replacement with St. Jude Medical Trifecta Bio-Prosthesis

Thrombocytopenia is a recognized complication following aortic valve replacement (AVR). While post-operative thrombotic thrombocytopenic purpura (TTP) is less common than heparin-induced thrombocytopenia (HIT), it is associated with high mortality and morbidity and prompt diagnosis and treatment is vital. In this case report, we describe the first reported case of TTP after AVR using the trifecta bio-prosthesis. We recommend that patients with severe and progressive thrombocytopenia following biological AVR should have early screening for both HIT and TTP, to shorten the decision-making process and provide the appropriate therapy.

Clinical and laboratory diagnosis of TTP: an integrated approach

Thrombotic thrombocytopenia purpura (TTP) is a rare, life-threatening disease with an incidence of approximately 2 persons per million per year. It is characterized by severe deficiency of the von Willebrand cleaving protease, ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13), leading to formation of platelet-rich thrombi in the microvasculature. Prompt initiation of appropriate therapy, particularly plasma exchange, may be life-saving. Diagnosis of TTP is challenging because of its diverse clinical manifestations, overlap in clinical presentation with other thrombotic microangiopathies, and limited availability of ADAMTS13 testing. Clinical prediction scores have been developed to estimate the pretest probability of severe ADAMTS13 deficiency and may be used as an adjunct to clinical judgment to guide initial management decisions. An ADAMTS13 activity level of less than 10% supports the diagnosis of TTP in appropriate clinical contexts, but many centers do not offer testing in-house and must send out the test to a reference laboratory with a turnaround time of several days. In such instances, initial management decisions must be made without the benefit of laboratory testing. In patients with TTP, inhibitor tests may be useful for distinguishing immune-mediated from congenital TTP. In this article, we review the epidemiology, natural history, and clinical presentation of TTP and laboratory assays for TTP including ADAMTS13 activity and inhibitor assays. We also describe an evidence-based approach to the evaluation of a patient with suspected TTP that integrates clinical and laboratory assessment.

Atypical Hemolytic-Uremic Syndrome: An Update on Pathophysiology, Diagnosis, and Treatment

Atypical hemolytic uremic syndrome (aHUS), a rare variant of thrombotic microangiopathy, is characterized by microangiopathic hemolytic anemia, thrombocytopenia, and renal impairment. The condition is associated with poor clinical outcomes with high morbidity and mortality. Atypical HUS predominantly affects the kidneys but has the potential to cause multi-organ system dysfunction. This uncommon disorder is caused by a genetic abnormality in the complement alternative pathway resulting in over-activation of the complement system and formation of microvascular thrombi. Abnormalities of the complement pathway may be in the form of mutations in key complement genes or autoantibodies against specific complement factors. We discuss the pathophysiology, clinical manifestations, diagnosis, complications, and management of aHUS. We also review the efficacy and safety of the novel therapeutic agent, eculizumab, in aHUS, pregnancy-associated aHUS, and aHUS in renal transplant patients.

Plasma von Willebrand Factor and a Disintegrin and Metalloproteinase with Eight Thrombospondin-type 1 Motif Levels in Hemodialysis Patients: Relation to Vascular Access Thrombosis

Vascular access complications are major issues in hemodialysis (HD) patients, which increase their morbidity and lessen HD efficiency. The aim of this study was to assess von Willebrand factor (VWF), and a disintegrin and metalloproteinase with eight thrombospondin-type 1 motif (ADAMTS13) levels in HD patients and their association with vascular access thrombosis (VAT). This study included a total of 158 individuals including 128 patients undergoing HD for more than 6 months, subdivided into two groups according to the occurrence of the previous episode of VAT; 60 HD patients with VAT and 68 HD patients without VAT and 30 healthy controls. Plasma ADAMTS13 and VWF levels were assessed by enzyme-linked immunosorbent assay technique. There were higher VWF levels and lower ADAMTS13 in HD patients, compared to healthy controls. Furthermore, VWF levels were significantly higher and ADAMTS13 levels were significantly lower in HD patients with VAT than those without VAT. Further prospective studies with large number of patients are thus needed to show if there is causal relationship between higher VWF levels, lower ADAMTS13, and VAT.

Concentration and Subclass Distribution of Anti-ADAMTS13 IgG Autoantibodies in Different Stages of Acquired Idiopathic Thrombotic Thrombocytopenic Purpura

Background

The acquired form of idiopathic thrombotic thrombocytopenic purpura (TTP) is an autoimmune disease, in which the underlying deficiency of the ADAMTS13 protease is caused by autoantibodies, predominantly of the IgG isotype. Certain HLA-DR-DQ haplotypes were associated with the risk of developing TTP.

Objectives

To investigate the development of the ADAMTS13-specific antibody response during the course of the disease, we analyzed the concentration, subclass distribution, and inhibitory potential of anti-ADAMTS13 IgG autoantibodies in samples of TTP patients drawn during the first acute phase, in remission, and during relapse. Additionally, we compared the anti-ADAMTS13 IgG levels between patients carrying and not carrying risk and protective HLA-DR-DQ haplotypes.

Patients and Methods

We determined the anti-ADAMTS13 IgG concentration and subclass distribution in 101 antibody-positive samples of 81 acquired TTP patients by ELISA methods. The presence and semi-quantitative amount of anti-ADAMTS13 inhibitors were determined in 97 of 100 deficient samples, and the specific inhibitory potential of anti-ADAMTS13 autoantibodies was determined in 49 selected samples, by mixing ADAMTS13-activity assays. HLA-DR-DQ typing and haplotype prediction were performed in 70 of the above patients.

Results

We found that IgG1 and IgG4 were the predominant subclasses, present in almost all samples. While IgG1 was the dominant subclass in almost half of the samples taken during the first acute episode, IgG4 was dominant in all samples taken during or following a relapse. The inhibitory potential of the samples correlated with levels of the IgG4 subclass. Anti-ADAMTS13 antibodies of IgG4-dominant samples had higher specific inhibitory potentials than IgG1-dominant samples, independently of disease stage. Interestingly, we found that patients carrying the protective DR7-DQ2 and DR13-DQ6 haplotypes had higher anti-ADAMTS13 IgG levels.

Conclusion

Our results indicate that IgG4 becomes the dominant subtype at some point of the disease course, apparently before the first relapse, parallel to the increase in inhibitory potential of the anti-ADAMTS13 autoantibodies. Furthermore, we found an association between the genetic background and the antibody response in TTP.

Bethesda Assay for Detecting Inhibitory Anti-ADAMTS13 Antibodies in Immune-Mediated Thrombotic Thrombocytopenic Purpura

A diagnosis of thrombotic thrombocytopenic purpura (TTP) is confirmed by a severe deficiency (<10%) of a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 (ADAMTS13) activity. Autoantibodies to ADAMTS13 can be detected with a simplified enzyme-linked immunosorbent assay (ELISA). An alternative methodology is a Bethesda assay, which has never been formally assessed in TTP. This study aimed to investigate the inhibitory anti-ADAMTS13 antibody assay and determine if the Bethesda assay is advantageous compared with the ELISA, measuring total immunoglobulin G (IgG) antibodies to ADAMTS 13. The Bethesda method determines the neutralizing activity of anti-ADAMTS13 antibodies in pooled normal plasma. We selected six immune-mediated TTP (iTTP) patients with ADAMTS13 activity levels <10% and strong ADAMTS13 inhibitors by 50:50 mixing studies and analyzed anti-ADAMTS13 antibodies using the Bethesda and ELISA assays. ADAMTS13 activity was stable at room temperature, while a time-dependent decrease in activity was detected in assay conditions of 37°C. Adding 5 mM Ca 2+ to citrated plasma prevented loss of ADAMTS13 activity with time. There was time dependence to the antibody-mediated inactivation, after 2-hour incubation. Two of the iTTP patients had no detectable ADAMTS13 antibodies by the Bethesda assay, but had high titer of anti-ADAMTS13 antibodies and low ADAMTS13 antigen levels. The Bethesda assay can only detect anti-ADAMTS13 antibodies that functionally inhibit ADAMTS13. The anti-ADAMTS13 IgG ELISA instead allows the rapid identification of total IgG autoantibodies, detecting both inhibitory and noninhibitory antibodies.

A rare combination of thrombotic thrombocytopenic purpura and antiphospholipid syndrome

: Thrombocytopenia, in the setting of microangiopathic hemolytic anemia and thrombotic events, is characteristic of both thrombotic thrombocytopenic purpura and primary antiphospholipid syndrome. Clinically, it is difficult to distinguish between these two syndromes. We present a 41-year-old woman with chronic, relapsing thrombotic thrombocytopenic purpura in the presence of antiphospholipid antibodies. She had clinical manifestations of antiphospholipid syndrome without meeting laboratory criteria of the Sydney classification system. In the literature, there have only been nine cases of thrombotic thrombocytopenic purpura associated with primary antiphospholipid syndrome. Seven of the nine cases suffered from one or multiple strokes, a common feature in antiphospholipid syndrome, but an uncommon finding in thrombotic thrombocytopenic purpura. We introduce the possibility of an association between thrombotic thrombocytopenic purpura and the presence of antiphospholipid antibodies. Systematic testing of ADAMTS13 activity and anti-ADAMTS13 antibodies in patients who present with neurological symptoms and thrombocytopenia, in the presence of antiphospholipid antibodies, may help with the diagnosis of the rare thrombotic thrombocytopenic purpura-antiphospholipid syndrome combination.