The utility of patient characteristics in predicting severe ADAMTS13 deficiency and response to plasma exchange

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.

A Saudi multicenter experience on therapeutic plasma exchange for patients with thrombotic thrombocytopenic purpura: A call for national registry

BACKGROUND

The improvement in the clinical care for patients with thrombotic thrombocytopenic purpura (TTP) is evolving, and many efforts are being put to standardize it. Here, we aimed to assess the provided care at a national level and identify deficiencies.

METHODS

A national Saudi retrospective descriptive study was carried out at six tertiary referral centers and included all patients who underwent therapeutic plasma exchange (TPE) for the diagnosis of TTP between May 2005, and July 2022. Collected information included demographic data, clinical features on presentation, and the results of laboratory investigations at admission and discharge. In addition, the number of TPE sessions, days till the first session of TPE, usage of immunological agents, and clinical outcomes were all collected.

RESULTS

One hundred patients were enrolled, predominantly female (56%). The mean age was 36.8 years. At diagnosis, 53% of patients showed neurological involvement. The mean platelet count at presentation was 21 × 109 /L. All patients had anemia (mean hematocrit 24.2%). Schistocytes were present in the peripheral blood film of all patients. The mean number of TPE rounds was 13 ± 9.3, and the mean days to start TPE since admission for the first episode was 2.5 days. ADAMTS13 level was measured in 48% of patients and was significantly low in 77% of them. Assessing for clinical TTP scores, 83%, 1000%, 64% of eligible patients had an intermediate/high PLASMIC, FRENCH, and Bentley scores, respectively. Caplacizumab was used on only one patient, and rituximab was administered to 37% of patients. A complete response for the first episode was achieved in 78% of patients. The overall mortality rate was 25%. Neither time to TPE, the use of rituximab or steroid affected survival.

CONCLUSIONS

Our study shows an excellent response to TPE with a survival rate approximate to the reported international literature. We observed a deficiency in using validated scoring systems in addition to confirming the disease by ADAMTS13 testing. This emphasizes the need for a national registry to facilitate proper diagnosis and management of this rare disorder.

Challenges in the diagnosis of thrombotic thrombocytopenic purpura

INTRODUCTION

Immune-mediated TTP (iTTP) is a rare condition without pathognomonic signs and symptoms. For this reason, the diagnosis of iTTP may be delayed or even missed, with potentially catastrophic consequences.

AREAS COVERED

The authors performed an extensive literature review on the diagnosis of iTTP and its challenges combined with their own experience in a referral center for patients with iTTP.

EXPERT OPINION

Although a definitive diagnosis of iTTP depends on the ADAMTS13 activity result, timely testing is rarely available at many centers to which patients present. If less complex tests were to become available, they would decrease the chances of late and/or missed diagnoses of iTTP throughout the world. While clinical scores to estimate the likelihood of iTTP exist, they are not well known, and can be misleading if used in the wrong context. Furthermore, the three scoring systems (PLASMIC, Bentley, and French) only moderately correlate with each other, which further complicates the landscape. The existence of these scores and how they should be used in practice is but one opportunity that can be seized through more robust programs to educate nonspecialist clinicians on how to recognize and treat patients with iTTP.

From the Discovery of ADAMTS13 to Current Understanding of Its Role in Health and Disease

ADAMTS13 (a disintegrin-like metalloprotease domain with thrombospondin type 1 motif, member 13) is a protease of crucial importance in the regulation of the size of von Willebrand factor multimers. Very low ADAMTS13 activity levels result in thrombotic thrombocytopenic purpura, a rare and life-threatening disease. The mechanisms involved can either be acquired (immune-mediated thrombotic thrombocytopenic purpura [iTTP]) or congenital (cTTP, Upshaw-Schulman syndrome) caused by the autosomal recessive inheritance of disease-causing variants (DCVs) located along the ADAMTS13 gene, which is located in chromosome 9q34. Apart from its role in TTP, and as a regulator of microthrombosis, ADAMTS13 has begun to be identified as a prognostic and/or diagnostic marker of other diseases, such as those related to inflammatory processes, liver damage, metastasis of malignancies, sepsis, and different disorders related to angiogenesis. Since its first description almost 100 years ago, the improvement of laboratory tests and the description of novel DCVs along the ADAMTS13 gene have contributed to a better and faster diagnosis of patients under critical conditions. The ability of ADAMTS13 to dissolve platelet aggregates in vitro and its antithrombotic properties makes recombinant human ADAMTS13 treatment a potential therapeutic approach targeting not only patients with cTTP but also other medical conditions.

Application of PLASMIC Score in Risk Prediction of Thrombotic Thrombocytopenic Purpura: Real-World Experience From a Tertiary Medical Center in Taiwan

Thrombotic thrombocytopenic purpura (TTP) is a life-threatening disorder caused by severe ADAMTS13 (a disintegrin and metalloprotease with thrombospondin type 1 repeats, member 13) deficiency (activity <10%). Urgent intervention based on the timely evaluation of ADAMTS13 level is crucial to guide optimal therapy. The recently developed PLASMIC score based on seven items allows the rapid identification of patients at high risk for TTP due to severe ADAMTS13 deficiency. This retrospective study included 31 hospitalized patients with suspicious thrombotic microangiopathy in National Cheng Kung University Hospital from December 2016 to July 2021. Data on ADAMTS13 activity and medical and laboratory information were retrieved from medical records. The PLASMIC score could be calculated in 24 of the 31 patients with available data, and the final cohort was stratified according to the 7-point PLASMIC score. All patients with high PLASMIC score (6-7) exhibited severe ADAMTS13 deficiency (activity ≤10%). One patient with a brain tumor and a PLASMIC score of 6 did not have severe ADAMTS13 activity of ≤10%. The patients in the intermediate- and low risk groups (PLASMIC scores of 5 and 0-4, respectively) exhibited ADAMTS13 activities of above 10%. Given the role of prompt diagnosis in the timely delivery of appropriate therapy, these findings confirm and strengthen the predictive value of the PLASMIC score in patients at high risk for TTP due to severe ADAMTS13 deficiency.

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.

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

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

Comparison of Clinical Scoring Systems in the Management of Patients with Microangiopathic Hemolytic Anemia and Thrombocytopenia

Objective:

Several clinical scoring systems have been developed for the differential diagnosis of thrombotic microangiopathies (TMAs), all to predict and identify patients with ADAMTS13 deficiency and to start treatment as soon as possible. The first scoring system in this regard was the Bentley score, and the French score and PLASMIC score were developed afterwards.

Materials and Methods:

We aimed to evaluate the laboratory parameters and clinical features of patients who underwent plasma exchange with a prediagnosis of TTP at our clinic between 2007 and 2019 and whose ADAMTS13 enzyme levels were measured and to compare the findings with the scoring systems.

Results:

Data of 35 patients were evaluated. Twelve patients were evaluated as high risk according to all three scoring systems. A statistically significant relation was observed between all three scoring systems and ADAMTS13 levels.

Conclusion:

A moderate correlation was found between all three scoring systems and ADAMTS13 levels. We observed similar potential strength of all three scoring systems to predict TTP among other TMAs and we conclude that they are applicable in daily practice.

MED-TMA: A clinical decision support tool for differential diagnosis of TMA with enhanced accuracy using an ensemble method

Considering difficulties in on-site ADAMTS13 testing and the performance instability of PLASMIC score according to ethnicity, we developed a prediction tool, MED-TMA (machine learning (ML) method for differential diagnosis (DDx) of thrombotic microangiopathy (TMA)) to support clinical decision. Data from 319 patients visiting 31 hospitals in Korea clinically diagnosed with primary TMA was randomly separated by 2:1 into two groups - the development dataset (D-set, n = 212), the validation dataset (V-set, n = 107). Feature elimination was conducted to select optimal clinical predictors. We developed the model with the selected features using ML methods, verifying using V-set. After the feature elimination using 19 clinical variables, five variables were selected with high importance value. Among nine ML methods, four ML methods were chosen considering the Area Under the Curves (AUC) and the correlation between the methods using D-set. We developed MED-TMA based on an optimized ensemble model with the selected four ML methods resulting in AUC values of 0.945 and 0.924 in D-set and V-set, respectively. In addition to the binary outcome, MED-TMA was capable of providing a probability for DDx of TMA. The ensemble approach driven MED-TMA showed comparable accurate and intuitive decision support for DDx of TMA to that of the existing models based on a single ML method. We provide a web-based nomogram for the appropriate use of effective but costly therapeutics to treat TMA patients (http://hematology.snu.ac.kr/medtma/).

Validation of PLASMIC score: an academic medical center case series (2012-present)

BACKGROUND

The PLASMIC score is a rapid and inexpensive tool for predicting severe ADAMTS13 deficiency (activity <10%) in patients with suspected thrombotic thrombocytopenic purpura (TTP) by analyzing seven parameters (platelet count; combined hemolysis variable; absence of active neoplasia; absence of an organ or stem-cell transplant; mean corpuscular value; international normalized ratio; and serum creatinine). The purpose of this study was to validate the PLASMIC score at a large multi-institutional academic medical center.

METHODS

An internal database of consultations to the transfusion medicine service, which oversees therapeutic apheresis at our institution, was reviewed to identify patients who were evaluated for and/or received plasma exchange for suspected TTP. These consultations covered the time period of January 2012 to February 2019. PLASMIC scoring criteria and ADAMTS13 assay results were abstracted from the electronic medical record, the PLASMIC score was calculated, and cases stratified into risk categories (low, intermediate, high risk) based on the score value.

RESULTS

Of 58 patients identified, 46 met inclusion criteria, and 27 demonstrated ADAMTS13 activity <10%. Correlation of severe ADAMTS13 deficiency with risk-stratified groups resulted in 78% sensitivity, 63% specificity, 75% positive predictive value (PPV), and 67% negative predictive value (NPV).

DISCUSSION

These findings paralleled those from validation studies performed at other institutions. They provided insufficient evidence to recommend routine use of the PLASMIC score to rule out TTP among patients at our hospitals. Nonetheless, these results reinforce the importance of early ADAMTS13 testing as a diagnostic triage tool for patients with suspected TTP.

Development and validation of a prediction model (AHC) for early identification of refractory thrombotic thrombocytopenic purpura using nationally representative data

Immune-mediated thrombotic thrombocytopenic purpura (iTTP) is a rare and life-threatening haematological emergency. Although therapeutic plasma exchange together with corticosteroids achieve successful outcomes, a considerable number of patients remain refractory to this treatment and require early initiation of intensive therapy. However, a method for the early identification of refractory iTTP is not available. To develop and validate a model for predicting the probability of refractory iTTP, a cohort of 265 consecutive iTTP patients from 17 large medical centres was retrospectively identified. The derivation cohort included 94 patients from 11 medical centres. For the validation cohort, we included 40 patients from the other six medical centres using geographical validation. An easy-to-use risk score system was generated, and its performance was assessed using internal and external validation cohorts. In the multivariable logistic analysis of the derivation cohort, three candidate predictors were entered into the final prediction model: age, haemoglobin and creatinine. The prediction model had an area under the curve of 0.886 (95% CI: 0.679-0.974) in the internal validation cohort and 0.862 (95% CI: 0.625-0.999) in the external validation cohort. The calibration plots showed a high agreement between the predicted and observed outcomes. In conclusion, we developed and validated a highly accurate prediction model for the early identification of refractory iTTP. It has the potential to guide tailored therapy and is a step towards more personalized medicine.

Typical and Atypical Hemolytic Uremic Syndrome in the Critically Ill

Hemolytic uremic syndrome is characterized by microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury. Disseminated intravascular coagulation, thrombotic thrombocytopenic purpura, and hemolytic uremic syndrome have a similar clinical presentation. Diagnostic needs to be prompt to decrease mortality, because identifying the different disorders can help to tailor specific, effective therapies. However, diagnosis is challenging and morbidity and mortality remain high, especially in the critically ill population. Development of clinical prediction scores and rapid diagnostic tests for hemolytic uremic syndrome based on mechanistic knowledge are needed to facilitate early diagnosis and assign timely specific treatments to patients with hemolytic uremic syndrome variants.

Shiga Toxin-Associated Hemolytic Uremic Syndrome: A Narrative Review

The severity of human infection by one of the many Shiga toxin-producing Escherichia coli (STEC) is determined by a number of factors: the bacterial genome, the capacity of human societies to prevent foodborne epidemics, the medical condition of infected patients (in particular their hydration status, often compromised by severe diarrhea), and by our capacity to devise new therapeutic approaches, most specifically to combat the bacterial virulence factors, as opposed to our current strategies that essentially aim to palliate organ deficiencies. The last major outbreak in 2011 in Germany, which killed more than 50 people in Europe, was evidence that an effective treatment was still lacking. Herein, we review the current knowledge of STEC virulence, how societies organize the prevention of human disease, and how physicians treat (and, hopefully, will treat) its potentially fatal complications. In particular, we focus on STEC-induced hemolytic and uremic syndrome (HUS), where the intrusion of toxins inside endothelial cells results in massive cell death, activation of the coagulation within capillaries, and eventually organ failure.

Expert statement on the ICU management of patients with thrombotic thrombocytopenic purpura

Thrombotic thrombocytopenic purpura (TTP) is fatal in 90% of patients if left untreated and must be diagnosed early to optimize patient outcomes. However, the very low incidence of TTP is an obstacle to the development of evidence-based clinical practice recommendations, and the very wide variability in survival rates across centers may be partly ascribable to differences in management strategies due to insufficient guidance. We therefore developed an expert statement to provide trustworthy guidance about the management of critically ill patients with TTP. As strong evidence was difficult to find in the literature, consensus building among experts could not be reported for most of the items. This expert statement is timely given the recent advances in the treatment of TTP, such as the use of rituximab and of the recently licensed drug caplacizumab, whose benefits will be maximized if the other components of the management strategy follow a standardized pattern. Finally, unanswered questions are identified as topics of future research on TTP.

Early Differentiation of Shiga Toxin-Associated Hemolytic Uremic Syndrome in Critically Ill Adults With Thrombotic Microangiopathy Syndromes

OBJECTIVES

Thrombotic microangiopathy syndromes are a heterogeneous group of severe diseases that often require ICU admission. Prompt initiation of targeted therapies is required for atypical hemolytic uremic syndrome and thrombotic thrombocytopenic purpura, whereas there is no specific consensus therapy for Shiga toxin-associated hemolytic uremic syndrome. We sought to compare the characteristics of Shiga toxin-associated hemolytic uremic syndrome, atypical hemolytic uremic syndrome, and thrombotic thrombocytopenic purpura patients at admission in the ICU to allow early differentiation of Shiga toxin-associated hemolytic uremic syndrome from other thrombotic microangiopathy syndromes and help to tailor initial treatment.

DESIGN

Retrospective cohort study.

SETTING

Two ICUs part of the French reference center for thrombotic microangiopathy syndromes.

PATIENTS

Adult patients presenting with features of thrombotic microangiopathy syndromes. Other causes than Shiga toxin-associated hemolytic uremic syndrome, atypical hemolytic uremic syndrome, and thrombotic thrombocytopenic purpura were excluded.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

From September 2003 to January 2017, 236 thrombotic microangiopathy syndrome patients were admitted, including 12 Shiga toxin-associated hemolytic uremic syndrome, 21 atypical hemolytic uremic syndrome, and 91 thrombotic thrombocytopenic purpura. Shiga toxin-associated hemolytic uremic syndrome patients were older than other thrombotic microangiopathy syndromes patients (64 yr [interquartile range, 50-72 yr] vs 42 yr [31-54 yr]; p = 0.007) and presented with more frequent digestive symptoms (92% vs 42%; p < 0.001), especially nonbloody diarrhea and vomiting. Biologically, Shiga toxin-associated hemolytic uremic syndrome patients displayed higher fibrinogen (490 mg/dL [460-540 mg/dL] vs 320 mg/dL [240-410 mg/dL]; p = 0.003) and creatinine levels (2.59 mg/dL [2.12-3.42 mg/dL] vs 1.26 mg/dL [0.61-1.90 mg/dL]; p < 0.001), and less marked anemia (hemoglobin level, 9.7 g/dL [8.7-11.9 g/dL] vs 7.7 g/dL [6.3-9.1 g/dL]; p < 0.001). Forty-two percent (n = 5) required renal replacement therapy, and 83% (n = 10) were treated with plasma exchange before the distinction from other thrombotic microangiopathy syndromes could be made.

CONCLUSIONS

Adult Shiga toxin-associated hemolytic uremic syndrome patients are older, present more frequently with digestive symptoms and display higher hemoglobin and fibrinogen levels than other thrombotic microangiopathy syndromes. However, overlap across the three thrombotic microangiopathy syndromes remains substantial, putting forward the need to implement early plasma therapy until thrombotic thrombocytopenic purpura and atypical hemolytic uremic syndrome can be ruled out.

Atypical haemolytic-uraemic syndrome in patient with metastatic colorectal cancer treated with fluorouracil and oxaliplatin: a case report and a review of literature

Background. Thrombotic microangiopathies (TMA) are relatively rare but severe disorders characterised by non-immune haemolytic anaemia, thrombocytopaenia and organ failure. In patients with metastatic cancer, sporadic forms of TMA can be triggered by chemotherapeutic agents or can occur as complication of malignancy itself or of infections.

Case report. Hereby, we report a case of a patient diagnosed with metastatic colorectal cancer who experienced an atypical haemolytic-uraemic syndrome (aHUS) during chemotherapy treatment with FOLFOX6 scheme. The use of eculizumab led to prompt recovery of laboratory parameters that was maintained despite treatment discontinuation due to appearance of pneumonia infectious. Additionally, genetic analyses revealed the presence in heterozygosis of CFH gene polymorphisms associated with aHUS.

Conclusion. This case emphasises the importance of considering TMA as a possible diagnosis in patients with cancer presenting with haemolytic non-immune mediate anaemia and thrombocytopaenia associated with worsening of renal function. Prompt diagnosis is crucial for the requirement of its specific treatment that can impact on long-term outcome and prognosis.

Critical developments of 2018: A review of the literature from selected topics in transfusion. A committee report from the AABB's Clinical Transfusion Medicine Committee

BACKGROUND

The AABB compiles an annual synopsis of the published literature covering important developments in the field of transfusion medicine. An abridged version of this work is being made available in TRANSFUSION, with the full-length report available as Appendix S1 (available as supporting information in the online version of this paper).

STUDY DESIGN AND METHODS

Papers published in late 2017 and 2018 are included, as well as earlier papers cited for background. Although this synopsis is comprehensive, it is not exhaustive, and some papers may have been excluded or missed.

RESULTS

The following topics are covered: "big data" and "omics" studies, emerging infections and testing, platelet transfusion and pathogen reduction, transfusion therapy and coagulation, transfusion approach to hemorrhagic shock and mass casualties, therapeutic apheresis, and chimeric antigen receptor T-cell therapy.

CONCLUSION

This synopsis may be a useful educational tool.

Thrombotic thrombocytopenic purpura: Toward targeted therapy and precision medicine

Thrombotic thrombocytopenic purpura (TTP) is a thrombotic microangiopathy characterized by severe congenital or immune-mediated deficiency in ADAMTS13, the enzyme that cleaves von Willebrand factor multimers. This rare condition leads invariably and rapidly to a fatal outcome in the absence of treatment, and therefore raises multiple diagnostic and therapeutic challenges. The novel concepts and mechanisms identified in the laboratory for this disease have been rapidly and successfully translated into the clinic for the benefit of patients, making TTP an archetypal disease that has benefited from targeted therapies. After decades of empirical treatment with plasma exchange, identification of ADAMTS13 as the key enzyme involved in TTP pathophysiology provided an explanation for the remarkable efficacy of plasma administration, in which the missing enzyme is replenished, and paved the way for development of a recombinant form of the enzyme. Similarly, the demonstration of a major role of anti-ADAMTS13 antibodies through models of passive transfer of autoimmunity spurred development of immunomodulatory strategies based on B-cell depletion. More recently, an inhibitor of the platelet-von Willebrand factor interaction demonstrated efficacy in large clinical trials through prevention of formation of further microthrombi and protection of organs from ischemia. These translational breakthroughs in TTP are described in our review.

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.

Cobalamin deficiency presenting with thrombotic microangiopathy (TMA) features: A systematic review

INTRODUCTION

Cobalamin deficiency may result in hematologic characteristics similar to thrombotic microangiopathy (TMA). To facilitate diagnosis, we reviewed reported cases of acquired cobalamin deficiency presenting with TMA features (c.def-TMA).

METHODS

A literature search identified reports of c.def-TMA. Deficiency was defined as B12 levels of <118 pmol/L. Corrected reticulocyte counts and reticulocyte production indexes were calculated. Clinical features were presented as proportion abnormal and results summarized as medians and interquartile ranges (IQR).

RESULTS

Patient level data was extracted from 41 identified cases. Median age (years) was 43 (30-55) with 21/41 (51%) being female. Cobalamin deficiency was noted in 35/40 (87.5%) but fold increases in MMA and HC were 30 and 6, respectively. The etiology was pernicious anemia in 28/41 (68%) cases. Anemia was both universal and severe, with hemoglobin levels of 55 g/L (4.7-6.6). Hypersegmented neutrophils were noted in 23/37 (62%), schistocytes in 29/38 (76%) and median LDH levels 3981 U/L (2004-5467). The RPI was <3.0% in all patients. Thrombocytopenia occurred in 33/41 (80.5%) with a median platelet count of 91 × 10⁹/L (42-112). Plasma infusion or exchange was initiated in 14/41 (34%) with associated complications in 2 cases.

CONCLUSION

Reticulocytopenia (RPI of <3.0%) was a universal finding that aids in differentiating c.def-TMA from other causes of hemolysis. C.def-TMA was associated with severe anemia, generally mild-moderate thrombocytopenia, and significant elevations in LDH.

Development and validation of a multivariable prediction rule for detecting a severe acquired ADAMTS13 activity deficiency in patients with thrombotic microangiopathies

Background:

Thrombotic microangiopathies (TMAs) are a group of diseases that have different aetiologies and treatments, but a clinical differential diagnosis remains difficult. Among TMAs, thrombotic thrombocytopenic purpura (TTP) is characterised by a severe ADAMTS13 functional deficiency. However, assays exploring ADAMTS13 activity are limited to some specialised laboratories. Our objective was to develop and validate a diagnostic method for TTP in adult patients with TMA.

Methods:

We generated a multivariable model (four predictors) on a cohort of 174 TMA patients in order to predict an ADAMTS13 activity deficiency (AUC of 0.927). The multivariable model was simplified into a binary rule to facilitate the interpretation of the predictions. There were two scenarios for a patient: (1) Predicted ADAMTS13 deficiency; if the patient met four conditions simultaneously (platelets ≤44×109/L, creatinine ≤2 mg/dL (≤176.84 µmol/L) for males or ≤1.9 mg/dL (≤168 µmol/L) for females, age ≤68 years and no history of haematopoietic stem cell transplant [HSCT]); or (2) Predicted “normal” activity; if any of the above conditions are not met. This rule was validated on a second cohort of 86 patients and performed with sensitivity of 87.7% and specificity of 92.7%.

Results and conclusions:

This could lead to the earlier confirmation or rapid exclusion of TTP when ADAMTS13 testing is not avalilable, facilitating a more suitable therapy based on the aetiology of the TMA.

Derivation and external validation of the PLASMIC score for rapid assessment of adults with thrombotic microangiopathies: a cohort study

BACKGROUND

Among the syndromes characterised by thrombotic microangiopathy, thrombotic thrombocytopenic purpura is distinguished by a severe deficiency in the ADAMTS13 enzyme. Patients with this disorder need urgent treatment with plasma exchange. Because ADAMTS13 activity testing typically requires prolonged turnaround times and might be unavailable in resource-poor settings, a method to rapidly assess the likelihood of severe ADAMTS13 deficiency is needed.

METHODS

All consecutive adult patients presenting to three large academic medical centres in Boston, MA, USA, with thrombotic microangiopathy and a possible diagnosis of thrombotic thrombocytopenic purpura between Jan 8, 2004, and Dec 6, 2015, were included in an ongoing multi-institutional registry (the Harvard TMA Research Collaborative). Univariate analysis was used to identify covariates for a logistic regression model predictive of severe ADAMTS13 deficiency (≤10% activity). A clinical point score was generated, and its diagnostic performance was assessed using internal and external validation cohorts and compared to clinical assessment alone.

FINDINGS

214 patients with thrombotic microangiopathy were included in the derivation cohort. A seven-component clinical prediction tool, termed the PLASMIC score, was developed and found to reliably assess the pretest probability of severe ADAMTS13 deficiency (C statistic 0·96, 95% CI 0·92-0·98). Our diagnostic model was reproducibly accurate in both the internal (0·95, 0·91-0·98) and external (0·91, 0·85-0·95) validation cohorts. The scoring system also more consistently diagnosed thrombotic microangiopathy due to severe ADAMTS13 deficiency than did standard clinical assessment, as measured by C statistic (0·96, 95% CI 0·92-0·98 for PLASMIC vs 0·83, 0·77-0·88 for clinical assessment; p<0·0001) and mean Brier score (0·065 for PLASMIC vs 0·111 for clinical assessment; mean paired difference 0·05, 95% CI 0·01-0·08; p<0·0001). When utilised in addition to clinical assessment, the PLASMIC score contributed significant discriminatory power (integrated discrimination improvement 0·24, 95% CI 0·11-0·37).

INTERPRETATION

We have developed and validated a clinical prediction tool-the PLASMIC score-to stratify patients with thrombotic microangiopathy according to their risk of having severe ADAMTS13 deficiency. We have shown that this scoring system is superior to standard clinical assessment in addressing the diagnostic challenge presented by thrombotic microangiopathy. Its use, together with clinical judgment, may facilitate treatment decisions in patients for whom timely results of ADAMTS13 activity testing are unavailable.

FUNDING

The Luick Family Fund of Massachusetts General Hospital.

The Alternative Pathway of Complement and the Evolving Clinical-Pathophysiological Spectrum of Atypical Hemolytic Uremic Syndrome

Complement-mediated atypical hemolytic uremic syndrome (aHUS) comprises approximately 90% of cases of aHUS, and results from dysregulation of endothelial-anchored complement activation with resultant endothelial damage. The discovery of biomarker ADAMTS13 has enabled a more accurate diagnosis of thrombotic thrombocytopenic purpura (TTP) and an appreciation of overlapping clinical features of TTP and aHUS. Given our present understanding of the pathogenic pathways involved in aHUS, it is unlikely that a specific test will be developed. Rather the use of biomarker data, complement functional analyses, genomic analyses and clinical presentation will be required to diagnose aHUS. This approach would serve to clarify whether a thrombotic microangiopathy present in a complement-amplifying condition arises from the unmasking of a genetically driven aHUS versus a time-limited complement storm-mediated aHUS due to direct endothelial damage in which no genetic predisposition is present. Although both scenarios result in the phenotypic expression of aHUS and involve the alternate pathway of complement activation, long-term management would differ.

A 35-year-old woman with influenza A-associated thrombotic thrombocytopenic purpura

A previously healthy 35-year-old woman presented with severe thrombotic thrombocytopenic purpura (TTP) affecting several organs and concomitant influenza A infection. On admission to hospital, haemoglobin was 5.4 g/dl, platelet count 6 × 10/l, Schistocyte count in peripheral blood 5%, and throat swab positive for influenza A RNA. The patient was treated with antiviral medication and transfusions of fresh frozen plasma before plasma exchange therapy with excellent response. Plasmaphereses were attenuated after 5 days, resulting in TTP relapse 3 days later. A disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 (ADAMTS13) protein was very low (<0.04 U/l) and anti-ADAMTS13 elevated (>2 U/l), consistent with acquired TTP. Platelet counts normalized after five additional plasma exchanges and oral corticosteroids. Antinuclear antibodies and subgroup anti-Ro/Sjögren's syndrome A antigen (SSA) were detected in serum and have remained borderline-elevated, although evaluation during TTP, recovery and follow-up have lacked clinical manifestations of connective tissue disease. Influenza A infection induced production of ADAMTS13 inhibitor, which resulted in TTP in a patient with circulating antinuclear antibodies, lacking other manifestations of connective tissue disease.

Absolute immature platelet count dynamics in diagnosing and monitoring the clinical course of thrombotic thrombocytopenic purpura

BACKGROUND

Thrombotic thrombocytopenic purpura (TTP) is a life-threatening diagnosis requiring prompt initiation of therapeutic plasma exchange (TPE). Measurement of immature platelet (PLT) fraction (%-IPF) differentiates PLT consumption or destruction from hypoproduction.

STUDY DESIGN AND METHOD

Our study evaluated %-IPF changes over the course of TTP treated with TPE and as a measure of treatment efficacy. Eleven idiopathic TTP patients, two human immunodeficiency virus (HIV)-associated TTP patients, and five non-TTP patients with thrombocytopenia were enrolled into our study. All patients were treated with TPE and had ADAMTS13 activity measured.

RESULTS

All idiopathic TTP patients had a significantly increased %-IPF and decreased absolute immature PLT count (A-IPC) and PLT count at presentation. An A-IPC value of less than 5 × 10(9) /L at presentation has 84.6% sensitivity, 80% specificity, and 91.7% positive predictive value for diagnosing TTP. A concurrent steady decline in %-IPF and increased PLT counts toward normal was observed in TTP patients undergoing TPE. The A-IPC, however, showed an increase and decrease curve that was not seen in the two HIV-associated TTP patients with no response to TPE and the five non-TTP patients. More importantly, reaching an A-IPC ratio of 3 compared to baseline value during TPE can readily differentiate idiopathic TTP from the other two groups and is correlated with good clinical responses to TPE. An abrupt increase of A-IPC during TPE was also noted in a TTP patient who relapsed 3 days before PLT count decrease. A-IPC is positively correlated with ADAMTS13 activity at presentation but negatively correlated with ADAMTS13 activity during recovery.

CONCLUSION

A-IPC should be routinely analyzed for diagnosing and monitoring TTP patients.

How I treat: the clinical differentiation and initial treatment of adult patients with atypical hemolytic uremic syndrome

Published data demonstrating the efficacy of complement inhibition therapy in patients with atypical hemolytic uremic syndrome (aHUS) are remarkable in contrast to the historically poor long-term prognosis for aHUS patients treated with plasma-based therapy. Although both aHUS and acquired thrombotic thrombocytopenic purpura (TTP) remain clinical diagnoses, an increased understanding of both conditions has improved our ability to differentiate aHUS from acquired TTP. These same data have also demonstrated the importance of a more rapid identification and diagnosis of aHUS as the recovery of end-organ injury present appears to be related to the time to initiate therapy with eculizumab. The diagnosis of acquired TTP can be confirmed by the finding of severely deficient ADAMTS13 activity (<10%) with evidence of an ADAMTS13 antibody inhibitor whereas merely deficient ADAMTS13 activity in the absence of an ADAMTS13 autoantibody is more consistent with congenital TTP. In the absence of an objective diagnostic test, clinicians must rely collectively on platelet count, serum creatinine, and ADAMTS13 activity in the context of the response to plasma exchange therapy to identify patients whose diagnosis is most consistent with aHUS, and thus be more likely to benefit from therapy with eculizumab.

Therapeutic plasma exchange in patients with thrombotic thrombocytopenic purpura: a retrospective multicenter study

Thrombotic thrombocytopenic purpura (TTP) is a particular form of thrombotic microangiopathy typically characterized by thrombocytopenia, microangiopathic hemolytic anemia, fever, neurological abnormalities, and renal dysfunction. TTP requires a rapid diagnosis and an adapted management in emergency. Daily sessions of therapeutic plasma exchange (TPE) remain the basis of management of TTP. Also, TTP is a rare disease that is fatal if it is not treated. TPE has resulted in excellent remission and survival rates in TTP patients.

AIM

We aimed to present our experience in 163 patients with TTP treated with TPE during the past 5years from 10 centers of Turkey.

PATIENTS AND METHODS

One hundered and sixty-three patients with TTP treated with TPE during the past 5years from 10 centers of Turkey were retrospectively evaluated. TPE was carried out 1-1.5times plasma volume. Fresh frozen plasma (FFP) was used as the replacement fluid. TPE was performed daily until normalization of serum lactate dehydrogenase (LDH) and recovery of the platelet count to >150×10(9)/dL. TPE was then slowly tapered. Clinical data, the number of TPE, other given therapy modalities, treatment outcomes, and TPE complications were recorded.

RESULTS

Fifty-eight percent (95/163) of the patients were females. The median age of the patients was 42years (range; 16-82). The median age of male patients was significantly higher than female (53 vs. 34years; p<0.001). All patients had thrombocytopenia and microangiopathic hemolytic anemia. At the same time, 82.8% (135/163) of patients had neurological abnormalities, 78.5% (128/163) of patients had renal dysfunction, and 89% (145/163) of patients had fever. Also, 10.4% (17/163) of patients had three of the five criteria, 10.4% (17/163) of patients had four of the five criteria, and 6.1% (10/163) of patients had all of the five criteria. Primary TTP comprised of 85.9% (140/163) of the patients and secondary TTP comprised of 14.1% (23/163) of the patients. Malignancy was the most common cause in secondary TTP. The median number of TPE was 13 (range; 1-80). The number of TPE was significantly higher in complete response (CR) patients (median 15.0 vs. 3.5; p<0.001). CR was achieved in 85.3% (139/163) of the patients. Similar results were achieved with TPE in both primary and secondary TTP (85% vs. 87%, respectively; p=0.806). There was no advantage of TPE+prednisolone compared to TPE alone in terms of CR rates (82.1% vs. 76.7%; p=0.746). CR was not achieved in 14.7% (24/163) of the patients and these patients died of TTP related causes. There were no statistical differences in terms of mortality rate between patients with secondary and primary TTP [15% (21/140) vs. 13% (3/23); p=0.806]. But, we obtained significant statistical differences in terms of mortality rate between patients on TPE alone and TPE+prednisolone [14% (12/86) vs. 3% (2/67), p<0.001].

CONCLUSIONS

TPE is an effective treatment for TTP and is associated with high CR rate in both primary and secondary TTP. Thrombocytopenia together with microangiopathic hemolytic anemia is mandatory for the diagnosis of TTP and if these two criteria met in a patient, TPE should be performed immediately.

Congenital thrombotic thrombocytopenic purpura (cTTP) with two novel mutations

Congenital thrombotic thrombocytopenic purpura (cTTP) is a rare disorder of childhood that has clinical and laboratory similarities to other, more common conditions. Prompt recognition is required as delays in therapy are associated with significant morbidity and failure to treat may lead to death. While the principles of treatment have not changed, enormous progress in the genetic and molecular understanding has taken place. Emerging treatment options may offer some hope of improved quality of life in future. We describe a Chinese patient with cTTP which resulted from two previously undescribed mutations in the ADAMTS13 gene.

Ten patient stories illustrating the extraordinarily diverse clinical features of patients with thrombotic thrombocytopenic purpura and severe ADAMTS13 deficiency

Patients with thrombotic thrombocytopenic purpura (TTP) and severe ADAMTS13 deficiency are often considered to have typical clinical features. However, our experience is that there is extraordinary diversity of the presenting features and the clinical courses of these patients. This diversity is illustrated by descriptions of 10 patients. The patients illustrate that ADAMTS13 activity may be normal initially but severely deficient in subsequent episodes. Patients with established diagnoses of systemic infection as the cause of their clinical features may have undetectable ADAMTS13 activity. Patients may have a prolonged prodrome of mild symptoms with only microangiopathic hemolytic anemia and thrombocytopenia or they may have the sudden onset of critical illness with multiple organ involvement. Patients may die rapidly or recover rapidly; they may require minimal treatment or extensive and prolonged treatment. Patients may have acute and severe neurologic abnormalities before microangiopathic hemolytic anemia and thrombocytopenia occur. Patients may have concurrent TTP and systemic lupus erythematosus. Patients may have hereditary ADAMTS13 deficiency as the etiology of their TTP rather than acquired autoimmune ADAMTS13 deficiency. These patients' stories illustrate the clinical spectrum of TTP with ADAMTS13 deficiency and emphasize the difficulties of clinical diagnosis.

Targeting von Willebrand factor and platelet glycoprotein Ib receptor

Atherothrombotic events, such as acute coronary syndrome or stroke, are the result of platelet activation. Von Willebrand factor (vWF), a multimeric glycoprotein, plays a key role in aggregation of platelets, especially under high-shear conditions. Acting as bridging element or ligand between damaged endothelial sites and the glycoprotein Ib (GPIb) receptor on platelets, vWF is responsible for platelet adhesion and aggregation. This vWF activation and further platelet aggregation mainly occurs under high shear stress present in small arterioles or during deficiency of the vWF-cleaving protease ADAMTS13. There are several substances targeting vWF itself or its binding receptor GPIb on platelets. Two antibodies are directed against vWF: AJW200, an IgG4 humanized monoclonal antibody, and 82D6A3, a monoclonal antibody of the collagen-binding A-3 domain of vWF. ALX-0081 and ALX-0681 are bivalent humanized nanobodies targeting the GPIb binding site of vWF. Aptamers are oligonucleotides with drug-like properties that share some of the attributes of monoclonal antibodies. ARC1779 is a second-generation, nuclease-resistant aptamer, binding to the activated vWF A1 domain and ARC15105 is a chemically advanced follower with an assumed higher affinity to vWF. Antibodies targeting GPIbα are h6B4-Fab, a murine monoclonal antibody; GPG-290, a recombinant, chimeric protein containing the amino-terminal 290 amino acids of GPIbα linked to human IgG1 Fc; and the monoclonal antibody SZ2. There are a number of promising preclinical results and development of some agents (AJW 200, ARC1779 and ALX-0081) has already reached Phase II trials.