Child-onset and adolescent-onset acquired thrombotic thrombocytopenic purpura with severe ADAMTS13 deficiency: a cohort study of the French national registry for thrombotic microangiopathy

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.

A Systematic Review of the Epidemiology and Disease Burden of Congenital and Immune-Mediated Thrombotic Thrombocytopenic Purpura

Congenital (cTTP) and immune-mediated (iTTP) thrombotic thrombocytopenic purpura are serious and rare clotting disorders resulting from a deficiency in the ADAMTS13 enzyme. A systematic review was conducted using the Ovid® MEDLINE & Embase databases to synthesize the epidemiology and burden of cTTP and iTTP worldwide (from January 1, 2010, to February 6, 2020, with an update that covered the period January 1, 2020-February 11, 2022). Outcomes of interest were incidence and prevalence of TTP, incidence of acute episodes, mortality, burden of illness (eg complications, healthcare utilization, patient-reported outcomes) and disease management. A total of 221 eligible observational studies were included. The incidence rate of acute episodes ranged from 0.19-0.35 person-years in adult patients with cTTP, and 1.81-3.93 per million persons per year for iTTP in the general population. Triggers of acute episodes were similar for cTTP and iTTP, with pregnancy and infection the most commonly observed. Exacerbation in patients with iTTP varied widely, ranging from 2.4-63.1%. All-cause mortality was observed in 0-13.4% of patients with cTTP, across studies and follow-up periods, and in 1.1% (median follow-up: 0.4 years) to 18.8% (1 year) of patients with iTTP during acute episodes. Cardiovascular, renal, and neurological disease were common complications. TTP also led to work disturbances, feelings of anxiety and depression, and general activity impairment. TTP treatment regimens used were generally reflective of current treatment guidelines. The evidence identified describes a high patient burden, highlighting the need for effective treatment regimens leading to improvements in outcomes. Considerable evidence gaps exist, particularly for disease epidemiology, patient-reported outcomes, costs of disease management, and associated healthcare resource utilization. This review may help increase disease awareness and highlights the need for additional real-world studies, particularly in geographical regions outside the United States and Western Europe.

Atypical Presentations of Pediatric-acquired Thrombotic Thrombocytopenic Purpura

BACKGROUND

Immune thrombotic thrombocytopenic purpura (iTTP) in children is a rare, severe thrombotic microangiopathy. This condition is characterized by microangiopathic hemolytic anemia, severe thrombocytopenia, and organ ischemia due to reduced activity of the von Willebrand factor-cleaving protease ADAMTS13.

METHODS

A retrospective case series evaluating data collected from the medical files of 4 children diagnosed with iTTP.

RESULTS

The presented case series depicts a variety of iTTP presentations: 1 case of primary iTTP, 1 case induced by Shiga toxin, 1 associated with RAS-associated autoimmune leukoproliferative disease (RALD), and 1 initial manifestation of systemic lupus erythematosus (SLE). Notably, 2 patients recovered without undergoing plasma exchange.

CONCLUSION

Early ADAMTS13 testing in children with unexplained hemolysis or thrombocytopenia is crucial. The diverse underlying causes, including infections and autoimmune disorders, underscore the complexity of iTTP in the pediatric population. These cases highlight the necessity for personalized treatment approaches that consider each patient's unique clinical situation and potential alternatives or modifications to conventional therapeutic regimens.

De-novo immune-mediated thrombotic thrombocytopenic purpura following surgical and non-surgical procedures: A systematic review

When de-novo immune-mediated thrombotic thrombocytopenic purpura (TTP) is diagnosed following an invasive procedure, clinical presentation patterns and outcomes are poorly defined. Therefore, in a systematic literature review of patients diagnosed with TTP following an invasive surgical or non-surgical procedure, we identified 19 studies reporting data on 25 patients. These data suggest that 1) TTP pathogenesis likely begins prior to the invasive procedure, 2) patients experience significant diagnostic delays, and 3) there is a high incidence of renal replacement therapy. Although invasive procedures may trigger TTP, further studies are needed to clarify the mechanisms underlying this association.

Successful Treatment of Acquired Thrombotic Thrombocytopenic Purpura With Caplacizumab Combined With Plasma Exchanges and Immune Suppression in 3 Children

Acquired thrombotic thrombocytopenic (aTTP) purpura is a life-threatening condition that can lead to devastating thromboembolic events. Recently, caplacizumab has been shown to rapidly restore platelet numbers and reduce the risk of severe end-organ damage when added to plasma exchanges (PEXs) and immunosuppression (IST). Here, we report the outcomes in 3 children with aTTP who were treated with caplacizumab in combination with PEXs and IST. In all 3 patients, platelet count increased to >15,000/mm 3 in 24 h and normalized on day 4, whereas normalization of ADAMTS13 activity >50% and elimination of the inhibitor was achieved after 18 to 89 days. Epistaxis was observed in 2 patients and was the only side effect related to caplacizumab. Caplacizumab is a promising agent for first-line treatment of children with aTTP.

Immune thrombotic thrombocytopenic purpura in older patients: Results from the Spanish TTP Registry (REPTT)

Immune thrombotic thrombocytopenic purpura (iTTP) is an ultra-rare disease that seldom occurs in the elderly. Few reports have studied the clinical course of iTTP in older patients. In this study, we have analysed the clinical characteristics at presentation and response to therapy in a series of 44 patients with iTTP ≥60 years at diagnosis from the Spanish TTP Registry and compared them with 209 patients with <60 years at diagnosis from the same Registry. Similar symptoms and laboratory results were described in both groups, except for a higher incidence of renal dysfunction among older patients (23% vs. 43.1%; p = 0.008). Front-line treatment in patients ≥60 years was like that administered in younger patients. Also, no evidence of a difference in clinical response and overall survival was seen in both groups. Of note, 14 and 25 patients ≥60 years received treatment with caplacizumab and rituximab, respectively, showing a favourable safety and efficacy profile, like that observed in patients <60 years.

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.

Bothrops venom-induced hemostasis disorders in the rat: Between Scylla and Charybdis

Hemostasis impairment represents the most threatening consequence of Viperidae envenoming, notably with Bothrops genus. In the French departments of America, B. atrox envenomation in French Guiana may lead to bleeding while B. lanceolatus envenomation in Martinique to thrombosis. Bleeding related to B. atrox envenomation is attributed to vascular damage mediated by venom metalloproteinases and blood uncoagulable state resulting from thrombocytopenia and consumptive coagulopathy. Thrombosis related to B. lanceolatus envenomation are poorly understood. We aimed to compare the effects of B. atrox and B. lanceolatus venoms in the rat to identify the determinants of the hemorrhagic versus thrombotic complications. Viscoelastometry (ROTEM), platelet count, plasma fibrinogen, thrombin generation assay, fibrinography, endothelial (von Willebrand factor, ADAMTS13 activity, ICAM-1, and soluble E-selectin), and inflammatory biomarkers (IL-1β, IL-6, TNF-α, MCP-1, and PAI-1) were determined in blood samples obtained at H3, H6, and H24 after the subcutaneous venom versus saline injection. In comparison to the control, initial fibrinogen consumption was observed with the two venoms while thrombocytopenia and reduction in the clot amplitude only with B. atrox venom. Moreover, we showed an increase in thrombin generation at H3 with the two venoms, an increase in fibrin generation accompanied with hyperfibrinogenemia at H24 and an increase in inflammatory biomarkers with B. lanceolatus venom. No endothelial damage was found with the two venoms. To conclude, our data support two-sided hemostasis complications in Bothrops envenoming with an initial risk of hemorrhage related to platelet consumption and hypocoagulability followed by an increased risk of thrombosis promoted by the activated inflammatory response and rapid-onset fibrinogen restoration.

Treatment Challenges of Acquired Thrombotic Thrombocytopenic Purpura in Pediatric Patients From a Low-Income Country

This study presents a comprehensive analysis of two cases of acquired thrombotic thrombocytopenic purpura (aTTP) observed in pediatric patients from a low-income country. In the instances described, both patients underwent a treatment regimen involving plasma exchange and immunosuppressive therapy conducted without the use of caplacizumab. Caplacizumab, an approved drug for adults known for its limited availability and high cost, has exhibited efficacy in reducing response time and recurrence frequency in aTTP cases. This approach resulted in significant clinical improvement and eventual remission of symptoms in one of the cases. These cases underscore the urgent necessity for a more inclusive approach in national health programs and international treatment guidelines. Specifically, there is a call to expand the existing comprehensive treatment algorithms to accommodate countries lacking access to caplacizumab. This adaptation aims to ensure the availability of suitable and effective treatment options for aTTP patients in regions facing limited pharmaceutical accessibility.

The Specificities of Thrombotic Thrombocytopenic Purpura at Extreme Ages: A Narrative Review

Thrombotic thrombocytopenic purpura (TTP) is a rare and life-threatening thrombotic microangiopathy (TMA) related to a severe ADAMTS13 deficiency, the specific von Willebrand factor (VWF)-cleaving protease. This deficiency is often immune-mediated (iTTP) and related to the presence of anti-ADAMTS13 autoantibodies that enhance its clearance or inhibit its VWF processing activity. iTTP management may be challenging at extreme ages of life. International cohorts of people with TTP report delayed diagnoses and misdiagnoses in children and elderly people. Child-onset iTTP shares many features with adult-onset iTTP: a female predominance, an idiopathic presentation, and the presence of neurological disorders and therapeutic strategies. Long-term follow-ups and a transition from childhood to adulthood are crucial to preventing iTTP relapses, in order to identify the occurrence of other autoimmune disorders and psychosocial sequelae. In contrast, older iTTP patients have an atypical clinical presentation, with delirium, an atypical neurological presentation, and severe renal and cardiac damages. They also have a poorer response to treatment and prognosis. Long-term sequelae are highly prevalent in older patients. Prediction scores for iTTP diagnoses are not used for children and have a lower sensitivity and specificity in patients over 60 years old. ADAMTS13 remains the unique biological marker that is able to definitely confirm or rule out the diagnosis of iTTP and predict relapses during follow-ups.

Adolescent acquired thrombotic thrombocytopenic purpura: An analysis of the Pediatric Health Information System database

The outcomes and characteristics of acquired thrombotic thrombocytopenic purpura (TTP) in adolescents is poorly understood due to an absence of studies focused on this population. To better understand the life-threatening disorder in this age, we performed an analysis of adolescent patients (ages 10-21) with TTP in the Pediatric Health Information Systems database from 2009 to 2020. The primary outcomes evaluated were in-hospital mortality and rate of TTP relapse. Secondary outcomes included rates of hemorrhagic and thrombotic complications during hospitalizations for TTP. Patients were included if they had a thrombotic microangiopathy diagnostic code, ADAMTS13 lab obtained, and received therapeutic plasmapheresis. Patients that received treatment for other non-TTP microangiopathies were excluded. A total of 99 patients with 123 hospitalizations for TTP treatment were identified. In-patient mortality occurred in 6 % (n = 6) and TTP relapse in 20 % (n = 20) of the cohort. Median time from initial admission to relapse was 33 days (IQR 15, 92). A hemorrhagic complication was identified in 29 % (n = 36) and thrombotic complication in 15 % (n = 19) of the cohort. The presence of underlying comorbidities was not associated with TTP relapse and only a diagnosis of cancer was associated with increased mortality. The rate of mortality and relapse in adolescent TTP is lower than that seen in adult registries. Long term prospective studies are needed to understand the long-term consequences of adolescent onset acquired TTP.

Ventricular Tachycardia in a Pediatric Patient with High-Risk Thrombotic Thrombocytopenia Purpura

An 8-year-old previously healthy male was diagnosed with thrombotic thrombocytopenic purpura (TTP) and increased serum cardiac troponin I. Telemetry recorded non-sustained ventricular tachycardia, without ST-segment changes or other abnormalities on serial electrocardiogram. This case illustrates that cardiac monitoring by telemetry should be considered in high-risk TTP with elevated cardiac troponin.

Recommendations for the diagnosis and treatment of patients with thrombotic thrombocytopenic purpura

Thrombotic thrombocytopenic purpura (TTP) is a thrombotic microangiopathy (TMA) characterized by the development of microangiopathic haemolytic anaemia, thrombocytopenia, and ischaemic organ dysfunction associated with ADAMTS13 levels lower than 10% in most cases. Recently there have been numerous advances in the field of PTT, new, rapid and accessible techniques capable of quantifying ADAMTS13 activity and inhibitors. The massive sequencing systems facilitate the identification of polymorphisms in the ADAMTS13 gene. In addition, new drugs such as caplacizumab have appeared and relapse prevention strategies are being proposed with the use of rituximab. The existence of TTP patient registries allow a deeper understanding of this disease but the great variability in the diagnosis and treatment makes it necessary to elaborate guidelines that homogenize terminology and clinical practice. The recommendations set out in this document were prepared following the AGREE methodology. The research questions were formulated according to the PICO format. A search of the literature published during the last 10 years was carried out. The recommendations were established by consensus among the entire group, specifying the existing strengths and limitations according to the level of evidence obtained. In conclusion, this document contains recommendations on the management, diagnosis, and treatment of TTP with the ultimate objective of developing guidelines based on the evidence published to date that allow healthcare professionals to optimize TTP treatment.

Molecular Diagnosis Is Vital to the Accurate Classification and Management of Thrombotic Thrombocytopenic Purpura in Children

Thrombotic thrombocytopenic purpura (TTP) is a rare but potentially life-threatening hematologic disease, presenting a myriad of diagnostic and management challenges in children. Here, we provide a review of this disorder and discuss 2 exemplary cases of TTP occurring in adolescents, emphasizing the need for consideration of late-onset congenital TTP (cTTP). We demonstrate the importance of early confirmation of ADAMTS13 enzyme deficiency and the presence or absence of ADAMTS13 inhibitor in order to rapidly initiate the appropriate life-saving therapies. Ultimately, molecular testing is paramount to distinguishing between congenital and acquired immune-mediated TTP.

Caplacizumab Model-Based Dosing Recommendations in Pediatric Patients With Acquired Thrombotic Thrombocytopenic Purpura

Acquired thrombotic thrombocytopenic purpura (aTTP) is a rare and life‐threatening autoimmune thrombotic microangiopathy. Caplacizumab, evaluated in phase II and III studies in adults, shortens the time to platelet count response and reduces aTTP exacerbations, has a favorable safety profile, and can potentially reduce refractoriness and mortality associated with aTTP. Since no children with aTTP were enrolled in these clinical trials, caplacizumab has been initially approved for use only in adult patients with aTTP (10 mg). Pediatric dosing recommendations were developed using model‐based simulations. A semimechanistic pharmacokinetic/pharmacodynamic population model has been developed describing the interaction between caplacizumab and von Willebrand factor antigen (vWF:Ag) following intravenous and subcutaneous administration of caplacizumab in different adult populations, at various dose levels, using nonlinear mixed‐effects modeling. Based on the allometrically scaled pharmacokinetic/pharmacodynamic model, different dosing regimens were simulated in 8000 children (aged 2‐18 years). Simulated caplacizumab exposures and vWF:Ag levels across different age categories were compared to an adult reference group. A simulated daily dose of 5 mg in children weighing <40 kg and of 10 mg in children weighing ≥40 kg resulted in similar exposures and vWF:Ag suppression across age and weight groups. Despite the lack of pediatric clinical data, the results of this modeling and simulation analysis constituted the basis for the European extension of indication for caplacizumab (10 mg) to adolescents aged >12 years and with a body weight ≥40 kg. This represents a rare case in which regulatory authorities have deemed a modeling and simulation study robust enough to approve a variation of indication.

Acute myocardial infarction and extensive systemic thrombosis in thrombotic thrombocytopenic purpura: A case report and review of literature

BACKGROUND

Thrombotic thrombocytopenic purpura (TTP) is a thrombotic microangiopathy characterized by the pentad of hemolytic anemia, fever, thrombocytopenia, renal failure, and neurological dysfunction. The formation of microthrombi in the arterioles and capillaries of various organs is one of the main pathophysiological mechanisms. Clinical manifestations of cardiac involvement in TTP patients are variable. Acute myocardial infarction has been reported as a complication with TTP as the secondary thrombotic event. Its emergence as the initial thrombotic event is extremely rare.

CASE SUMMARY

A 49-year-old previously healthy man was admitted for fever, typical angina chest pain 3 d prior to presentation, and newly onset left lower limb pain. The electrocardiogram illustrated ST-elevation acute myocardial infarction of the antero-lateral wall of the left ventricle. Transthoracic echocardiography depicted two large thrombi at the apex of the left ventricle and moderately reduced ejection fraction (40%). Venous Doppler ultrasound showed occlusion of the left popliteal artery. Laboratory tests showed severe thrombocytopenia, mild hemolytic anemia, elevated D-dimers, and high troponin and creatine kinase-MB. Abdominal computed tomography revealed other thrombotic sites (superior mesenteric artery, posterior aortic wall, spleen and renal infarction, and ileum necrosis). He was immediately started on steroids and addressed to surgery for acute abdominal pain. After an initial stabilization of the hematological deficit, he went into general surgery for resection of the necrotic ileum but died soon after the intervention due to multiple organ failure.

CONCLUSION

Cardiac involvement in TTP patients is common, challenging and more often fatal, especially when other thrombotic complications coexist.

Congenital ADAMTS-13 deficiency presenting as life-threatening thrombosis during pregnancy

Thrombotic thrombocytopenic purpura (TTP) is a life-threatening disease characterised by thrombocytopenia, microangiopathic haemolytic anaemia and microvascular thrombosis. Congenital TTP accounting for less than 5% of all TTP cases can have a late presentation in adulthood mostly triggered by predisposing factors such as infection, pregnancy and inflammation. We present a case of a 23-year-old woman who presented to us in the postpartum period with mesenteric artery thrombosis with infarcts and later was diagnosed as a case of TTP based on congenital a disintegrin and metalloproteinase with thrombospondin type 1 repeats 13 (ADAMTS-13) deficiency detected on ADAMTS-13 levels and gene sequencing. She was successfully managed initially with therapeutic plasma exchanges and is now on prophylactic fortnightly fresh frozen plasma infusions at 15 mL/kg body weight and continues to be in remission.

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.

[Treatment of thrombotic thrombocytopenic purpura]

The review discusses approaches to treatment of congenital thrombotic thrombocytopenic purpura (TTP) or Upshaw-Schulman syndrome. In congenital TTP, plasma transfusions are sufficient. Such treatment options as plasma exchange, administration of clotting factor VIII concentrate, recombinant ADAMTS13, are also used. Separately discussed issues of management of patients with TTP during pregnancy, and pediatric patients with TTP.

[Treatment of thrombotic thrombocytopenic purpura]

The review discusses approaches to treatment of acquired thrombotic thrombocytopenic purpuгa (aTTP). In patients with aTTP plasma exchanges, glucocorticosteroids allow to stop an acute attack of TTP, and use of rituximab allows to achieve remission. In recent years, caplacizumab has been used. Treatment options such as cyclosporin A, bortezomib, splenectomy, N-acetylcysteine, recombinant ADAMTS13 are also described. Separately discussed issues of management of patients with TTP during pregnancy, and pediatric patients with TTP.

[Recurrent thrombocytopenia with hemolytic anemia in a boy aged 3 years]

A boy, aged 3 years and 8 months, had recurrent thrombocytopenia with hemolytic anemia for more than 3 years. The physical examination showed no enlargement of the liver, spleen, and lymph nodes or finger deformities. Laboratory results showed a negative result of the direct antiglobulin test, normal coagulation function, and increases in bilirubin, lactate dehydrogenase and reticulocytes. The results of von Willebrand factor-cleaving protease ADAMTS13 activity assay showed extreme deficiency, and antibody assay showed negative ADAMTS13 inhibitory autoantibodies. Next-generation sequence showed compound heterozygous mutation in the ADAMTS13 gene. The boy was diagnosed with congenital thrombotic thrombocytopenic purpura. This disease may be easily misdiagnosed as Evans syndrome and is difficult to diagnose in clinical practice. The child had developed the disease since birth, but it took 3 years to make a confirmed diagnosis. Therefore, congenital thrombotic thrombocytopenic purpura should be considered for children with jaundice at birth, recurrent thrombocytopenia with hemolytic anemia, and negative results of the direct antiglobulin test. The detection of ADAMTS13 activity and ADAMTS13 inhibitory autoantibodies should be performed as soon as possible for a definite diagnosis, and gene detection should be performed to make a confirmed diagnosis when necessary.

Recognizing and managing hereditary and acquired thrombotic thrombocytopenic purpura in infants and children

We describe how infants and children with hereditary and acquired autoimmune thrombotic thrombocytopenic purpura (TTP) initially present and how they can be promptly diagnosed and effectively managed. These are uncommon disorders that are commonly misdiagnosed and can be rapidly fatal. TTP is caused by a severe deficiency of the plasma protease, A disintegrin and Metalloprotease with a ThromboSpondin type 1 motif, member 13 (ADAMTS13). Measurement of ADAMTS13 activity is becoming easily accessible. A common presentation of hereditary TTP is neonatal severe hemolysis and hyperbilirubinemia. However, the median age of diagnosis is not until 5.5 years. Plasma is effective treatment for exacerbations and for prophylaxis. Plasma may be replaced by recombinant ADAMTS13 when it becomes available. Acquired TTP is more frequent in older children, in whom it is more common in girls and is commonly associated with systemic lupus erythematosus. For acquired TTP, plasma exchange and immunosuppression are the current treatment for acute episodes; caplacizumab is now commonly used in adults and may replace plasma exchange.

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.

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.

Diagnosis and follow-up of thrombotic thrombocytopenic purpura with an automated chemiluminescent ADAMTS13 activity immunoassay

BACKGROUND

Thrombotic thrombocytopenic purpura (TTP) is a life-threatening thrombotic microangiopathy (TMA) caused by a severe functional deficiency in ADAMTS13 (a disintegrin and metalloprotease with thrombospondin type I repeats-13), the specific von Willebrand factor (VWF) cleaving protease. ADAMTS13 activity is essential to diagnose TTP but remains challenging to assess, as reference ADAMTS13 activity assays are manual and time consuming. Current techniques also lack robustness in low detectable ADAMTS13 activity range, which could prove problematic for therapy-driven monitoring.

OBJECTIVES

The HemosIL AcuStar ADAMTS13 activity assay is a fast, automated chemiluminescent assay, the performance of which remains to be evaluated prospectively on very large cohorts of patients with TMA and in real-life conditions.

PATIENTS AND METHODS

Our study was conducted over two successive sequences: a retrospective evaluation followed by a "real-life" prospective evaluation. Overall, we evaluated the HemosIL AcuStar ADAMTS13 activity assay on 539 citrated plasma samples. We extensively studied linearity, limit of detection, contamination, intra-assay and interassay precisions with a specific focus on levels < 25 IU/dL. Diagnostic performances for the detection of < 10 IU/dL ADAMTS13 activity and overall method comparison were conducted with the fluorescence resonance energy transfer (FRETS)-VWF73 assay as the reference method.

RESULTS

Technical performance proved excellent. Robustness in low detectable ADAMTS13 activity range was good, potentially qualifying this assay for therapy-driven monitoring. Comparison with the FRETS-VWF73 assay was satisfactory (r 2 = .83, P < .0001) as were the diagnostic performances for acute-phase TTP (specificity, 99.7%; positive predictive value, 99.2%).

CONCLUSION

The HemosIL AcuStar ADAMTS13 activity assay is a fast, reliable, automated technique well adapted as a first-line ADAMTS13 activity assay for TTP diagnosis and follow-up.

Insights from the Hereditary Thrombotic Thrombocytopenic Purpura Registry: Discussion of Key Findings Based on Individual Cases from Switzerland

The Hereditary TTP Registry is an international cohort study for patients with a confirmed or suspected diagnosis of hereditary thrombotic thrombocytopenic purpura (hTTP) and their family members. Hereditary TTP is an ultra-rare blood disorder (prevalence of ∼1-2 cases per million), the result of autosomal-recessively inherited congenital ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) deficiency (ADAMTS13 activity <10% of the normal), and associated with yet many unanswered questions. Until December 2017, the Hereditary TTP Registry had enrolled 123 confirmed hTTP patients. Their median age at disease onset was 4.5 years (range: 0-70) and at clinical diagnosis 16.7 years (range: 0-69), a difference that highlights the existing awareness gap in recognizing hTTP. The systematic collection of clinical data of individual patients revealed their substantial baseline comorbidities, as a consequence of recurring TTP episodes in the past. Most notable was the high proportion of patients having suffered from premature arterial thrombotic events, mainly transient ischemic attacks, ischemic strokes, and to a lesser extent myocardial infarctions. At 40 to 50 years of age and above, more than 50% of patients had suffered from at least one such event, and many had experienced arterial thrombotic events despite regular plasma infusions every 2 to 3 weeks that supplements the missing plasma ADAMTS13. The article by van Dorland et al. (Haematologica 2019;104(10):2107-2115) and the ongoing Hereditary TTP Registry cohort study were recognized with the Günter Landbeck Excellence Award at the 50th Hemophilia Symposium in Hamburg in November 2019, the reason to present the Hereditary TTP Registry in more detail here.

A critical evaluation of caplacizumab for the treatment of acquired thrombotic thrombocytopenic purpura

Introduction: Acquired thrombotic thrombocytopenic purpura (aTTP) is a thrombotic microangiopathy caused by inhibitory autoantibodies against ADAMTS13 protein. Until recently, the combination of plasma exchange (PEX) and immunosuppression has been the standard front-line treatment in this disorder. However, aTTP-related mortality, refractoriness, and relapse are still a matter of concern. Areas covered: The better understanding of the pathophysiological mechanisms of aTTP has allowed substantial improvements in the diagnosis and treatment of this disease. Recently, the novel anti-VWF nanobody caplacizumab has been approved for acute episodes of aTTP. Caplacizumab is capable to block the adhesion of platelets to VWF, therefore inhibiting microthrombi formation in the ADAMTS13-deficient circulation. In this review, the characteristics of caplacizumab together with the available data of its efficacy and safety in the clinical setting will be analyzed. Besides, the current scenario of aTTP treatment will be provided, including the role of other innovative drugs. Expert opinion: With no doubt, caplacizumab is going to change the way we treat aTTP. In combination with standard treatment, caplacizumab can help to significantly reduce aTTP-related mortality and morbidity and could spare potential long-term consequences by minimizing the risk of exacerbation.

Thrombotic thrombocytopenic purpura and defective apoptosis due to CASP8/10 mutations: the role of mycophenolate mofetil

Immunological dysregulation may underlie unusual autoimmune diseases, which also deserve to be investigated from a genetic point of view.

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.

Successful treatment of plasma exchange-refractory thrombotic thrombocytopenic purpura with rituximab: A case report

BACKGROUND

Thrombotic thrombocytopenic purpura (TTP), a subtype of thrombotic microangiopathy, has a very high fatality rate if there is no timely diagnosis or treatment. Here, we report a case of TTP refractory to high displacement plasma exchange, which was later successfully treated with rituximab.

CASE SUMMARY

Here we report a case of refractory TTP in a 63-year-old woman with a low platelet count and decreased ADAMTS13 activity. Her platelet count was 9 × 10⁹/L, hemoglobin level was 81 g/L, and ADAMTS13 was < 5%. She was diagnosed with thrombotic thrombocytopenic purpura. After 8 d of daily plasma exchange (PEX), her platelet levels were still low. However, after 6 d of treatment with rituximab, her platelet count increased and ADAMTS13 activity returned to normal.

CONCLUSION

PEX can cure most patients, but the relapse rate can be up to 50%-60%. This case suggested that rituximab can improve the curative efficiency of PEX and prevent disease relapse in TTP.

Hemolytic uremic syndrome in a developing country: Consensus guidelines

BACKGROUND

Hemolytic uremic syndrome (HUS) is a leading cause of acute kidney injury in children. Although international guidelines emphasize comprehensive evaluation and treatment with eculizumab, access to diagnostic and therapeutic facilities is limited in most developing countries. The burden of Shiga toxin-associated HUS in India is unclear; school-going children show high prevalence of anti-factor H (FH) antibodies. The aim of the consensus meeting was to formulate guidelines for the diagnosis and management of HUS in children, specific to the needs of the country.

METHODS

Four workgroups performed literature review and graded research studies addressing (i) investigations, biopsy, genetics, and differential diagnosis; (ii) Shiga toxin, pneumococcal, and infection-associated HUS; (iii) atypical HUS; and (iv) complement blockade. Consensus statements developed by the workgroups were discussed during a consensus meeting in March 2017.

RESULTS

An algorithm for classification and evaluation was developed. The management of Shiga toxin-associated HUS is supportive; prompt plasma exchanges (PEX) is the chief therapy in patients with atypical HUS. Experts recommend that patients with anti-FH-associated HUS be managed with a combination of PEX and immunosuppressive medications. Indications for eculizumab include incomplete remission with plasma therapy, life-threatening features, complications of PEX or vascular access, inherited defects in complement regulation, and recurrence of HUS in allografts. Priorities for capacity building in regional and national laboratories are highlighted.

CONCLUSIONS

Limited diagnostic capabilities and lack of access to eculizumab prevent the implementation of international guidelines for HUS in most developing countries. We propose practice guidelines for India, which will perhaps be applicable to other developing countries.

Acquired thrombotic thrombocytopenia purpura associated with severe ADAMTS13 deficiency in a 3-year-old boy: a case report and review of the literature

Background

Acquired thrombotic thrombocytopenia purpura is very rarely encountered in children. It is often misdiagnosed initially when the condition is not inherited.

Case presentation

We describe a 3-year-old Malay boy who presented with simple febrile seizure and had no neurological deficit, however, he was found to have microangiopathic hemolytic anemia, thrombocytopenia, and elevated serum lactate dehydrogenase. An ADAMTS13 assay results showed zero activities (0%), and markedly high level of ADAMTS13 inhibitor (93.15 U/mL) confirming the diagnosis of secondary thrombotic thrombocytopenia purpura. He received fresh frozen plasma infusions for 3 days and subsequently his platelet levels normalized. Serial ADAMTS13 assay results showed improvement. He was also given a short course of prednisolone after which the ADAMTS13 activity normalized (> 114%) at the end of prednisolone course.

Conclusions

At presentation, acquired thrombotic thrombocytopenia purpura in a very young child is commonly misdiagnosed as other conditions like idiopathic thrombocytopenic purpura, Evans syndrome, atypical hemolytic-uremic syndrome, or malignancy. ADAMTS13 assay should be performed early when thrombotic thrombocytopenia purpura is suspected as this condition is associated with dire consequences.

Pediatric thrombotic thrombocytopenic purpura

Child-onset thrombotic thrombocytopenic purpura (TTP) is a rare entity of thrombotic microangiopathy (TMA). The pathophysiology of the disease is based on a severe functional deficiency of ADAMTS13 (activity <10%), the specific von Willebrand factor (VWF)-cleavage protease. This deficiency may be either acquired (associated anti-ADAMTS13 autoantibodies) or congenital (resulting from biallelic mutations of ADAMTS13 gene). ADAMTS13 deficiency is responsible for the accumulation of high molecular weight multimers of VWF and the formation of platelet thrombi in the microcirculation. Consequently, microangiopathic hemolytic anemia and consumption thrombocytopenia are associated with organ ischemia. The differential diagnosis with other TMAs, autoimmune cytopenias or hematological malignancies may be challenging. The exploration of ADAMTS13 (activity, antibodies, antigen, ADAMTS13 gene) supports the diagnosis of TTP. The first-line treatment of the acute phase of TTP is based on plasmatherapy. In congenital TTP, patients with a chronic disease benefit from a prophylactic plasmatherapy. In autoimmune TTP, steroids and B-cells depleting therapies increasingly are used together with plasma exchange. Long-term follow-up including the monitoring of ADAMTS13 activity is mandatory. A severe decrease in ADAMTS13 activity (<10%) may predict relapses and preemptive B-cell depletion with rituximab can be used to prevent relapses.

Dissecting the pathophysiology of immune thrombotic thrombocytopenic purpura: interplay between genes and environmental triggers

Although outstanding progress has been made in understanding the pathophysiology of thrombotic thrombocytopenic purpura (TTP), knowledge of the immunopathogenesis of the disease is only at an early stage. Anti-ADAMTS13 auto-antibodies were shown to block proteolysis of von Willebrand factor and/or induce ADAMTS13 clearance from the circulation. However, it still remains to identify which immune cells are involved in the production of anti-ADAMTS13 autoantibodies, and therefore account for the remarkable efficacy of the B-cell depleting agents in this disease. The mechanisms leading to the loss of tolerance of the immune system towards ADAMTS13 involve the predisposing genetic factors of the human leukocyte antigen class II locus DRB1*11 and DQB1*03 alleles as well as the protective allele DRB1*04, and modifying factors such as ethnicity, sex and obesity. Future studies have to identify why these identified genetic risk factors are also frequently to be found in the healthy population although the incidence of immune-mediated thrombotic thrombocytopenic purpura (iTTP) is extremely low. Moreover, the development of recombinant ADAMTS13 opens a new therapeutic era in the field. Interactions of recombinant ADAMTS13 with the immune system of iTTP patients will require intensive investigation, especially for its potential immunogenicity. Better understanding of iTTP immunopathogenesis should, therefore, provide a basis for the development of novel therapeutic approaches to restore immune tolerance towards ADAMTS13 and thereby better prevent refractoriness and relapses in patients with iTTP. In this review, we address these issues and the related challenges in this field.

Thrombotic thrombocytopenic purpura

Thrombotic thrombocytopenic purpura (TTP) is a rare and life-threatening thrombotic microangiopathy characterized by microangiopathic hemolytic anemia, severe thrombocytopenia, and organ ischemia linked to disseminated microvascular platelet rich-thrombi. TTP is specifically related to a severe deficiency in ADAMTS13 (a disintegrin and metalloprotease with thrombospondin type 1 repeats, member 13), the specific von Willebrand factor-cleaving protease. ADAMTS13 deficiency is most frequently acquired via ADAMTS13 autoantibodies, but rarely, it is inherited via mutations of the ADAMTS13 gene. The first acute episode of TTP usually occurs during adulthood, with a predominant anti-ADAMTS13 autoimmune etiology. In rare cases, however, TTP begins as soon as childhood, with frequent inherited forms. TTP is ∼2-fold more frequent in women, and its outcome is characterized by a relapsing tendency. Rapid recognition of TTP is crucial to initiate appropriate treatment. The first-line therapy for acute TTP is based on daily therapeutic plasma exchange supplying deficient ADAMTS13, with or without steroids. Additional immune modulators targeting ADAMTS13 autoantibodies are mainly based on steroids and the humanized anti-CD20 monoclonal antibody rituximab. In refractory or unresponsive TTP, more intensive therapies including twice-daily plasma exchange; pulses of cyclophosphamide, vincristine, or cyclosporine A; or salvage splenectomy are considered. New drugs including N-acetylcysteine, bortezomib, recombinant ADAMTS13, and caplacizumab show promise in the management of TTP. Also, long-term follow-up of patients with TTP is crucial to identify the occurrence of other autoimmune diseases, to control relapses, and to evaluate psychophysical sequelae. Further development of both patients’ registries worldwide and innovative drugs is still needed to improve TTP management.