An update on pathogenesis and diagnosis of thrombotic thrombocytopenic purpura

A Case Report of Congenital Thrombotic Thrombocytopenic Purpura: The Peripheral Blood Smear Lights the Diagnosis

We report on a 12-year-old boy with congenital thrombotic thrombocytopenic purpura, on who had an erroneous diagnosis as chronic immune thrombocytopenia. The patient presented with complaints of jaundice and skin rash. Laboratory analysis showed nonimmune hemolytic anemia and severe thrombocytopenia. Peripheral blood smear showed 8% schistocytes, polychromasia, and anisocytosis. The ADAMTS13 antigen and activity were suspected to be lower than 5% with any antibodies against the enzyme. The DNA sequence analyses resulted in compound heterozygosity consisting of c.291_391del in exon 3 and c.4143dupA in exon 29. Schistocyte (fragmented erythrocytes) on the peripheral blood smear is a light that illuminates the diagnosis. Early recognition of the disease can prevent inappropriate treatments and morbidities due to organ damage.

Residues R1075, D1090, R1095, and C1130 Are Critical in ADAMTS13 TSP8-Spacer Interaction Predicted by Molecular Dynamics Simulation

ADAMTS13 (A Disintegrin and Metalloprotease with Thrombospondin type 1 repeats, member 13) cleaves von Willebrand Factor (VWF) multimers to limit the prothrombotic function of VWF. The deficiency of ADAMTS13 causes a lethal thrombotic microvascular disease, thrombotic thrombocytopenic purpura (TTP). ADAMTS13 circulates in a “closed” conformation with the distal domain associating the Spacer domain to avoid off-target proteolysis or recognition by auto-antibodies. However, the interactions of the distal TSP8 domain and the Spacer domain remain elusive. Here, we constructed the TSP8-Spacer complex by a combination of homology modelling and flexible docking. Molecular dynamics simulation was applied to map the binding sites on the TSP8 or Spacer domain. The results predicted that R1075, D1090, R1095, and C1130 on the TSP8 domain were key residues that interacted with the Spacer domain. R1075 and R1095 bound exosite-4 tightly, D1090 formed multiple hydrogen bonds and salt bridges with exosite-3, and C1130 interacted with both exosite-3 and exosite-4. Specific mutations of exosite-3 (R568K/F592Y/R660K/Y661F/Y665F) or the four key residues (R1075A/D1090A/R1095A/C1130A) impaired the binding of the TSP8 domain to the Spacer domain. These results shed new light on the understanding of the auto-inhibition of ADAMTS13.

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.

Thrombotic thrombocytopenic purpura complicated with acute aortic dissection: A case report

RATIONALE

Thrombotic thrombocytopenic purpura (TTP) is a critical thrombotic microangiopathy involving multiple organs. To the best of our knowledge, there are no reports of TTP complicated by acute aortic dissection.

PATIENT CONCERNS

We herein described a 53-year-old male with TTP who did not have a significant medical history. After immediate plasma exchange and glucocorticoid therapy, the patient's clinical condition improved. However, the patient suddenly experienced chest pain with elevated blood pressure.

DIAGNOSES

Computed tomography angiography suggested acute type B aortic dissection.

INTERVENTIONS

The patient was immediately transferred to the cardiac aortic surgery department for thoracic aortic endovascular repair.

OUTCOMES

The patient was discharged after successful thoracic aortic endovascular repair. Unfortunately, 3 months later, the patient experienced chest and back pain at home and died suddenly, possibly due to the recurrence of aortic dissection.

LESSONS

Even if patients have no identifiable risk factors, physicians should be aware of this rare and life-threatening acute complication of TTP, which may have multiple causes, including preexisting connective tissue disease, abnormal blood pressure fluctuations, and increased risk of hemorrhage. Early identification and timely treatment of acute aortic dissection are critical for improving prognosis.

Thrombotic microangiopathy during pregnancy

Pregnancy is a high-risk time for the development of different kinds of thrombotic microangiopathy (TMA). Three major syndromes including TTP (thrombotic thrombocytopenic purpura), PE/HELLP (preeclampsia/hemolysis, elevated liver function tests, low platelets), and aHUS (atypical hemolytic- uremic syndrome) should be sought in pregnancy-TMA. These severe disorders share multiple clinical features and overlaps and even the coexistence of more than one pathologic mechanism. Each of these disorders finally ends in endothelial damage and fibrin thrombi formation within the microcirculation that fragments RBCs (schystocytes), aggregates platelets, and creates ischemic injury in the targeted organs i.e.; kidney and brain. Although the mechanisms of these severe disorders have been revealed, pregnancy-related TMA still interfaces with diagnostic and therapeutic challenges. Here, we highlight the current knowledge of diagnosis and management of these complications during pregnancy.

Bleeding and Thrombosis: Insights into Pathophysiology of Bothrops Venom-Related Hemostasis Disorders

Toxins from Bothrops venoms targeting hemostasis are responsible for a broad range of clinical and biological syndromes including local and systemic bleeding, incoagulability, thrombotic microangiopathy and macrothrombosis. Beyond hemostais disorders, toxins are also involved in the pathogenesis of edema and in most complications such as hypovolemia, cardiovascular collapse, acute kidney injury, myonecrosis, compartmental syndrome and superinfection. These toxins can be classified as enzymatic proteins (snake venom metalloproteinases, snake venom serine proteases, phospholipases A₂ and L-amino acid oxidases) and non-enzymatic proteins (desintegrins and C-type lectin proteins). Bleeding is due to a multifocal toxicity targeting vessels, platelets and coagulation factors. Vessel damage due to the degradation of basement membrane and the subsequent disruption of endothelial cell integrity under hydrostatic pressure and tangential shear stress is primarily responsible for bleeding. Hemorrhage is promoted by thrombocytopenia, platelet hypoaggregation, consumption coagulopathy and fibrin(ogen)olysis. Onset of thrombotic microangiopathy is probably due to the switch of endothelium to a prothrombotic phenotype with overexpression of tissue factor and other pro-aggregating biomarkers in association with activation of platelets and coagulation. Thrombosis involving large-caliber vessels in B. lanceolatus envenomation remains a unique entity, which exact pathophysiology remains poorly understood.

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.

First report of a de novo iTTP episode associated with an mRNA-based anti-COVID-19 vaccination

Thrombotic thrombocytopenic purpura (TTP) is a rare but potentially life-threatening thrombotic microangiopathy, characterized by disseminated thrombus formation in the microvasculature, causing severe organ failure. Immune-mediated TTP (iTTP) is occasionally described after vaccination, especially against viral agents. We report a case of a 38-year-old woman with a de novo iTTP after exposure to the mRNA-based anti-coronavirus disease 2019 (COVID-19) vaccine produced by Pfizer-BioNTech. She presented with increased bruising and petechiae starting 2 weeks after receiving the first dose of the anti-COVID-19 vaccine. Laboratory data revealed a severe ADAMTS13-deficiency in combination with a very high autoantibody titer against ADAMTS13. She was successfully treated with plasma exchange, corticosteroids, rituximab, and caplacizumab. To our knowledge, this is the first case report of iTTP after mRNA-based COVID-19 vaccination in a previously TTP-naïve patient.

Unresponsive Thrombotic Thrombocytopenic Purpura (TTP): Challenges and Solutions

Thrombotic thrombocytopenic purpura (TTP) is a thrombotic microangiopathy secondary to a severely decreased A Disintegrin And Metalloprotease with ThromboSpondin type 1 repeats 13 (ADAMTS13) activity, resulting in the formation of widespread von Willebrand factor - and platelet-rich microthrombi. ADAMTS13 deficiency is mainly acquired through anti-ADAMTS13 autoantibodies in adults. With modern standards of care, unresponsive TTP has become rarer with a frequency of refractory/relapsing forms dropping from >40% to <10%. As patients with unresponsive TTP are at increased risk of mortality, prompt recognition and early therapeutic intensification are mandatory. Therapeutic options at the disposal of clinicians caring for patients with refractory TTP consist of increased ADAMTS13 supplementation, increased immunosuppression, and inhibition of von Willebrand factor adhesion to platelets. In this work, we focus on possible therapies for the management of patients with unresponsive TTP, and propose an algorithm for the management of these difficult cases.

N-glycan-mediated shielding of ADAMTS13 prevents binding of pathogenic autoantibodies in immune-mediated TTP

Immune-mediated thrombotic thrombocytopenic purpura (iTTP) is an autoimmune disorder caused by the development of autoantibodies targeting different domains of ADAMTS13. Profiling studies have shown that residues R568, F592, R660, Y661, and Y665 within exosite-3 of the spacer domain provide an immunodominant region of ADAMTS13 for pathogenic autoantibodies that develop in patients with iTTP. Modification of these 5 core residues with the goal of reducing autoantibody binding revealed a significant tradeoff between autoantibody resistance and proteolytic activity. Here, we employed structural bioinformatics to identify a larger epitope landscape on the ADAMTS13 spacer domain. Models of spacer-antibody complexes predicted that residues R568, L591, F592, K608, M609, R636, L637, R639, R660, Y661, Y665, and L668 contribute to an expanded epitope within the spacer domain. Based on bioinformatics-guided predictions, we designed a panel of N-glycan insertions in this expanded epitope to reduce the binding of spacer domain autoantibodies. One N-glycan variant (NGLY3-ADAMTS13, containing a K608N substitution) showed strongly reduced reactivity with TTP patient sera (28%) as compared with WT-ADAMTS13 (100%). Insertion of an N-glycan at amino acid position 608 did not interfere with processing of von Willebrand factor, positioning the resulting NGLY3-ADAMTS13 variant as a potential novel therapeutic option for treatment of iTTP.

Immune-mediated thrombotic thrombocytopenic purpura in childhood treated by caplacizumab, about 3 cases

Immune-mediated thrombotic thrombocytopenic purpura (iTTP) is a rare disease in adults and exceptional in childhood. Caplacizumab has proven its effectiveness in the treatment of iTTP in adulthood in association with standard of care. Unfortunately, this treatment is restricted to adults. We report our experience in three children who were treated successfully with caplacizumab.

Therapeutic Plasma Exchange in the Critically Ill Patient: Technology and Indications

Therapeutic plasma exchange (TPE) is frequently the most common Apheresis Medicine technique used for extracorporeal therapy of a wide variety of renal, neurological, hematological, and other clinical indications. Many of these clinical indications require intensive care during critical illness. Conventional TPE uses one of two main technical methods to achieve the goal of removing known disease mediators from the plasma: using centrifugal forces to separate and remove components of blood, or a membrane filtration method that separates plasma from the cellular components of blood. The following review discusses the basic principles of TPE, the technological aspects, and relevant clinical scenarios encountered in the intensive care unit, including relevant guidelines and recommendations from the American Society for Apheresis.

[Diagnosis of thrombotic thrombocytopenic purpura]

Thrombotic thrombocytopenic purpura (TTP) is a rare, life-threatening disease, disease, characterised by microangiopathic hemolytic anaemia, consumption thrombocytopenia, and organ dysfunction. The pathogenesis of TTP is attributed to the deficiency in the activity of the metalloproteinase ADAMTS13, specific von Willebrand factor cleaving protease. TTP is suspected when detecting microangiopathic hemolytic anemia, thrombocytopenia, damage to various organs. Diagnosis of TTP is confirmed by the detection of ADAMTS13 activity in plasma less than 10%. Plasma samples for the study of ADAMTS13 activity should be taken before the start of plasma transfusions or plasma exchange. In patients with severe ADAMTS-13 deficiency autoantibodies anti-ADAMTS13 and inhibitor ADAMTS13 should be investigated. Anti-ADAMTS13 antibodies belonging to IgG not always have inhibitory effects. The inhibitory effect of anti-ADAMTS13 antibodies is confirmed by mixing test. All patients with the first established diagnosis of TTP should be examined for mutations of the ADAMTS13 gene.

ISTH guidelines for the diagnosis of thrombotic thrombocytopenic purpura

BACKGROUND

Despite an increase in our understandings of pathogenesis of thrombotic thrombocytopenic purpura (TTP), the approaches for initial diagnosis and management of TTP vary significantly.

OBJECTIVE

The evidence-based guidelines of the International Society on Thrombosis and Haemostasis (ISTH) are intended to support patients, clinicians, and other health care professionals in their decisions about the initial diagnosis and management of acute TTP.

METHODS

In June 2018, ISTH formed a multidisciplinary panel that included hematologists, an intensive care physician, nephrologist, clinical pathologist, biostatistician, and patient representatives, as well as a methodology team from McMaster University. The panel composition was designed to minimize the potential conflicts of interests. The panel used the Grading of Recommendations Assessment, Development, and Evaluation approach and the Population, Intervention, Comparison, Outcome framework to develop and grade their recommendations. Public comments were sought and incorporated in the final document.

RESULTS

The panel agreed on three recommendations covering the initial diagnosis with emphasis on the importance of ADAMTS13 testing (eg, activity, anti-ADAMTS13 IgG or inhibitor) and assessment of the pretest probability of TTP by clinical assessment and/or the risk assessment models like the PLASMIC or French score. The panel noted how availability and turnaround time of ADAMTS13 test results might affect early diagnosis and management, in particular the use of caplacizumab.

CONCLUSIONS

There is a lack of high-quality evidence to support strong recommendations for the initial diagnosis and management of a suspected TTP. The panel emphasized the importance of obtaining ADAMTS13 testing in a proper clinical context. Future research should focus on how to monitor and act on ADAMTS13 levels during remission.

Understanding the Health Literacy in Patients With Thrombotic Thrombocytopenic Purpura

Following an acute thrombotic thrombocytopenic purpura (TTP) episode, patients are at risk for relapse, and a careful long-term follow-up is needed. Adherence to the follow-up by patients implies a good understanding of the disease. However, TTP literacy in patients is currently unknown. To explore the TTP literacy in patients and identify factors associated with poor disease understanding, a questionnaire was developed focusing on patient's characteristics, knowledge about TTP and patients' actions in an emergency. The questionnaire was presented to 120 TTP patients in remission from the French National Registry for Thrombotic Microangiopathies. TTP literacy was low in 24%, intermediate in 43% and high in 33% of the patients. Low TTP literacy was associated with older age and low education level. Among the knowledge gaps identified, few patients knew that plasma exchange in acute phase is mandatory and has to be done daily (39%), 47% of participants did not consider themselves at risk for relapse, and 30% of women did not know that pregnancy exposes them to a greater risk of relapse. Importantly, few patients responded about life-saving actions in an emergency. Hence, the design of educational material should pay special attention to the age and education level of the target population focusing on the events leading to TTP, the importance of the emergency treatment, controllable predisposing factors for TTP development and patient attitude in an emergency.

Efficacy of albumin and compounded plasma for plasma exchange in acquired thrombotic thrombocytopenic purpura

INTRODUCTION

Thrombotic thrombocytopenic purpura (TTP) is a rare life-threatening thrombotic microangiopathy. Therapeutic plasma exchange (TPE) is the first-line treatment for TTP. In our institution, albumin plus plasma (fresh frozen plasma [FFP] and/or cryoprecipitate-reduced plasma [CRP]) has been used as replacement fluid since 2014. We aimed to evaluate the efficacy of albumin combined with plasma as TPE for TTP.

MATERIAL AND METHODS

We retrospectively evaluated 20 patients admitted to our institution due to an acute episode of TTP between January 1, 2014 and February 1, 2019. They were divided into two groups according to the replacement fluid protocols: (a) albumin plus FFP (1:1) and (b) albumin plus mixed plasma [ie, albumin and FFP with CRP (2:1:1)] groups. Data on patient characteristics, replacement parameters, outcome, and hemorrhage risk were collected and analyzed.

RESULTS

There were no significant differences in treatment outcomes between the two groups (P > .05). However, the albumin plus mixed plasma group tended to require fewer plasma exchanges (median, 4) and shorter time to response (median, 15 days) compared to albumin plus FFP group (median, 6; 31 days). Although the cumulative survival of the albumin plus mixed plasma group was higher than the other group starting from day 23 after treatment, we did not observe significant difference (P = .50). No significant increase in the risk for hemorrhage was observed in either group.

CONCLUSIONS

The therapeutic efficacy of albumin and mixed plasma (2:1:1) is not inferior to that of albumin and FFP (1:1), and it can be used in treating TTP.