Pathophysiology of thrombotic thrombocytopenic purpura

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

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

Hereditary thrombotic thrombocytopenic purpura and COVID-19: Impacts of vaccination and infection in this rare disease

Introduction

Severe COVID-19 is associated with an important increase of von Willebrand factor and mild lowering of ADAMTS13 activity that may, in the presence of a strong inflammatory reaction, increase the risk of acute thrombotic thrombocytopenic purpura (TTP). Although acute episodes of immune-mediated TTP associated with COVID-19 or SARS-CoV-2 vaccination have been reported, data about clinical evolution of hereditary TTP (hTTP) during the pandemic are scarce.

Method

We conducted a survey among adult patients of the International Hereditary TTP Registry about SARS-CoV-2 vaccination, COVID-19, and occurrence of acute hTTP episodes.

Results

Of 122 adult hTTP patients invited to participate, 86 (70.5%) responded. Sixty-five had been vaccinated (75.6%), of which 14 had received in addition a booster, resulting in 139 individual vaccine shots. Although vaccinations in patients on plasma prophylaxis were done within 1 week of the last plasma infusion, all 23 patients treated with plasma on demand were vaccinated without prior plasma infusions. One patient on uninterrupted weekly plasma infusions presented within 3 days from his second vaccination with neurological symptoms and computed tomography scan 9 days later showed subacute ischemic/hemorrhagic frontal lobe infarction. A second male patient developed acute myocarditis after his second dose of mRNA-1273 vaccine. Twelve (14%) patients had COVID-19, associated with an acute hTTP episode in three of them: one patient had a transient ischemic attack, one a stroke, and a pregnant woman was hospitalized to intensify plasma treatment.

Discussion

The risk of an acute episode triggered by COVID-19 seems higher than following vaccination in hTTP patients, who can be safely vaccinated against SARS-CoV-2.

Refractory Thrombotic Thrombocytopenic Purpura to Therapeutic Plasma Exchange

Thrombotic thrombocytopenic purpura (TTP) is a rare, potentially fatal hematologic disorder characterized by microangiopathic hemolytic anemia, thrombocytopenia, and varying signs of visceral ischemia secondary to microvascular thrombosis. TTP is caused by a severe deficiency of ADAMTS13, a protease enzyme responsible for cleaving von Willebrand-factor (vWF) multimers. First-line therapy with plasmapheresis has increased survival rates immensely; however, there are few reported cases that are refractory to standardized treatment. We describe two cases of refractory TTP successfully managed with the addition of caplacizumab, an anti-von Willebrand factor immunoglobulin fragment that inhibits the interaction of vWF multimers with platelets.

Real-world data with the use of caplacizumab in the treatment of acquired thrombotic thrombocytopenic purpura: A single-center with homogeneous treatment experience

BACKGROUND

Recently, real-world data confirmed the effectiveness of caplacizumab in the treatment of acquired thrombotic thrombocytopenic purpura (aTTP); however, limitations as different treatment protocols from multicenter experiences and the front-line use of rituximab could overshadow the real impact of the addition of caplacizumab.

STUDY DESIGN AND METHODS

We report the clinical characteristics and response to treatment of 30 consecutive cases of aTTP treated under a homogeneous therapeutic protocol with the only exception of the addition of caplacizumab in the last 10 cases (caplacizumab group), whose primary outcome we compare with the previous 20 cases (control group).

RESULTS

Caplacizumab was started at a median of 2.5 days after diagnosis (interquartile range [IQR] 1-4) and maintained for a median of 37.5 days (IQR 32-39). Safety was in line with previous reports with 30% of patients showing mild adverse events, the most common bleeding. The caplacizumab group achieved platelet count normalization after a median of 3 (IQR 2-5) versus 4 (IQR 2-8.5) days in the control group (p = .067). The caplacizumab group required a lower median number of plasma exchanges, 10 (IQR 9-11) versus 16.5 (IQR 11-20) in the control group (p = .0053) and a shorter length of hospitalization, 12 (IQR 12-14) vs. 22 (IQR 15-27) days (p = .0025). There were no refractory cases and no deaths in the caplacizumab group compared to five refractory cases and three aTTP-related death (15%) in the control group.

DISCUSSION

Our experience confirms improvement in the outcomes with a decrease in refractoriness and mortality since the introduction of caplacizumab.

Thromboinflammation: From Atherosclerosis to COVID-19

The activating interplay of thrombosis and inflammation (thromboinflammation) has been established as a major underlying pathway, driving not only cardiovascular disease but also autoimmune disease and most recently, COVID-19. Throughout the years, innate immune cells have emerged as important modulators of this process. As the most abundant white blood cell in humans, neutrophils are well-positioned to propel thromboinflammation. This includes their ability to trigger an organized cell death pathway with the release of decondensed chromatin structures called neutrophil extracellular traps. Decorated with histones and cytoplasmic and granular proteins, neutrophil extracellular traps exert cytotoxic, immunogenic, and prothrombotic effects accelerating disease progression. Distinct steps leading to extracellular DNA release (NETosis) require the activities of PAD4 (protein arginine deiminase 4) catalyzing citrullination of histones and are supported by neutrophil inflammasome. By linking the immunologic function of neutrophils with the procoagulant and proinflammatory activities of monocytes and platelets, PAD4 activity holds important implications for understanding the processes that fuel thromboinflammation. We will also discuss mechanisms whereby vascular occlusion in thromboinflammation depends on the interaction of neutrophil extracellular traps with ultra-large VWF (von Willebrand Factor) and speculate on the importance of PAD4 in neutrophil inflammasome assembly and neutrophil extracellular traps in thromboinflammatory diseases including atherosclerosis and COVID-19.

Endothelial VWF is critical for the pathogenesis of vaso-occlusive episode in a mouse model of sickle cell disease

Vaso-occlusive episode (VOE) is a common and critical complication of sickle cell disease (SCD). Its pathogenesis is incompletely understood. von Willebrand factor (VWF), a multimeric plasma hemostatic protein synthesized and secreted by endothelial cells and platelets, is increased during a VOE. However, whether and how VWF contributes to the pathogenesis of VOE is not fully understood. In this study, we found increased VWF levels during tumor necrosis factor (TNF)-induced VOE in a humanized mouse model of SCD. Deletion of endothelial VWF decreased hemolysis, vascular occlusion, and organ damage caused by TNF-induced VOE in SCD mice. Moreover, administering ADAMTS13, the VWF-cleaving plasma protease, reduced plasma VWF levels, decreased inflammation and vaso-occlusion, and alleviated organ damage during VOE. These data suggest that promoting VWF cleavage via ADAMTS13 may be an effective treatment for reducing hemolysis, inflammation, and vaso-occlusion during VOE.

Real-world effectiveness of caplacizumab vs the standard of care in immune thrombotic thrombocytopenic purpura

Immune thrombotic thrombocytopenic purpura (iTTP) is a thrombotic microangiopathy caused by anti-ADAMTS13 antibodies. Caplacizumab is approved for adults with an acute episode of iTTP in conjunction with plasma exchange (PEX) and immunosuppression. The objective of this study was to analyze and compare the safety and efficacy of caplacizumab vs the standard of care and assess the effect of the concomitant use of rituximab. A retrospective study from the Spanish TTP Registry of patients treated with caplacizumab vs those who did not receive it was conducted. A total of 155 patients with iTTP (77 caplacizumab, 78 no caplacizumab) were included. Patients initially treated with caplacizumab had fewer exacerbations (4.5% vs 20.5%; P < .05) and less refractoriness (4.5% vs 14.1%; P < .05) than those who were not treated. Time to clinical response was shorter when caplacizumab was used as initial treatment vs caplacizumab used after refractoriness or exacerbation. The multivariate analysis showed that its use in the first 3 days after PEX was associated with a lower number of PEX (odds ratio, 7.5; CI, 2.3-12.7; P < .05) and days of hospitalization (odds ratio, 11.2; CI, 5.6-16.9; P < .001) compared with standard therapy. There was no difference in time to clinical remission in patients treated with caplacizumab compared with the use of rituximab. No severe adverse event was described in the caplacizumab group. In summary, caplacizumab reduced exacerbations and refractoriness compared with standard of care regimens. When administered within the first 3 days after PEX, it also provided a faster clinical response, reducing hospitalization time and the need for PEX.

The role of VWF/FVIII in thrombosis and cancer progression in multiple myeloma and other hematological malignancies

Cancer associated thrombosis (CAT) is associated with significant morbidity and mortality, highlighting an unmet clinical need to improve understanding of the pathophysiology of CAT. Multiple myeloma (MM) is associated with one of the highest rates of thrombosis despite widespread use of thromboprophylactic agents. The pathophysiology of thrombosis in MM is multifactorial and patients with MM appear to display a hypercoagulable phenotype with potential contributory factors including raised von Willebrand factor (VWF) levels, activated protein C resistance, impaired fibrinolysis, and abnormal thrombin generation. In addition, the toxic effect of anti-myeloma therapies on the endothelium and contribution to thrombosis has been widely described. Elevated VWF/factor VIII (FVIII) plasma levels have been reported in heterogeneous cohorts of patients with MM and other hematological malignancies. In specific studies, high plasma VWF levels have been shown to associate with VTE risk and reduced overall survival. While the mechanisms underpinning this remain unclear, dysregulation of the VWF and A Disintegrin And Metalloprotease Thrombospondin type 1, motif 13 (ADAMTS-13) axis is evident in certain solid organ malignancies and correlates with advanced disease and thrombosis. Furthermore, thrombotic microangiopathic conditions arising from deficiencies in ADAMTS-13 and thus an accumulation of prothrombotic VWF multimers have been reported in patients with MM, particularly in association with specific myeloma therapies. This review will discuss current evidence on the pathophysiological mechanisms underpinning thrombosis in MM and in particular summarize the role of VWF/FVIII in hematological malignancies with a focus on thrombotic risk and emerging evidence for contribution to disease progression.

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

Introduction

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

Methods

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

Results

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

Conclusion

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

Deletion of platelet CLEC-2 decreases GPIbα-mediated integrin αIIbβ3 activation and decreases thrombosis in TTP

Microvascular thrombosis in patients with thrombotic thrombocytopenic purpura (TTP) is initiated by GPIbα-mediated platelet binding to von Willebrand factor (VWF). Binding of VWF to GPIbα causes activation of the platelet surface integrin αIIbβ3. However, the mechanism of GPIbα-initiated activation of αIIbβ3 and its clinical importance for microvascular thrombosis remain elusive. Deletion of platelet C-type lectin-like receptor 2 (CLEC-2) did not prevent VWF binding to platelets but specifically inhibited platelet aggregation induced by VWF binding in mice. Deletion of platelet CLEC-2 also inhibited αIIbβ3 activation induced by the binding of VWF to GPIbα. Using a mouse model of TTP, which was created by infusion of anti-mouse ADAMTS13 monoclonal antibodies followed by infusion of VWF, we found that deletion of platelet CLEC-2 decreased pulmonary arterial thrombosis and the severity of thrombocytopenia. Importantly, prophylactic oral administration of aspirin, an inhibitor of platelet activation, and therapeutic treatment of the TTP mice with eptifibatide, an integrin αIIbβ3 antagonist, reduced pulmonary arterial thrombosis in the TTP mouse model. Our observations demonstrate that GPIbα-mediated activation of integrin αIIbβ3 plays an important role in the formation of thrombosis in TTP. These observations suggest that prevention of platelet activation with aspirin may reduce the risk for thrombosis in patients with TTP.

Alternate-day dosing of caplacizumab for immune-mediated thrombotic thrombocytopenic purpura

BACKGROUND

The anti-von Willebrand factor (VWF) nanobody caplacizumab directly prevents the fatal microthrombi formation in immune-mediated thrombotic thrombocytopenic purpura (iTTP), thereby adding a new therapeutic principle to the treatment of this disorder. However, real-world treatment modalities beyond clinical trials remain heterogeneous.

METHODS

Here, we describe the risks and benefits of an alternate-day dosing regimen for caplacizumab by thoroughly analyzing the timing and outcome of this approach in a retrospective cohort of 25 iTTP patients treated with caplacizumab at seven different medical centers in Austria and Germany between 2018 and 2021.

RESULTS

Alternate-day dosing of caplacizumab appeared feasible and led to persisting normal platelet counts in most patients. Five patients experienced iTTP exacerbations or relapses that led to the resumption of daily caplacizumab application. VWF activity was repeatedly measured in 16 of 25 patients and documented sufficient suppression by caplacizumab after 24 and 48 h in line with published pharmacodynamics.

CONCLUSION

Extension of caplacizumab application intervals from daily to alternate-day dosing may be safely considered in selected patients after 3 to 4 weeks of daily treatment. Earlier modifications may be discussed in low-risk patients but require close monitoring for clinical and laboratory features of thrombotic microangiopathy.

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.

Cardiovascular disease is a leading cause of mortality among TTP survivors in clinical remission

Immune-mediated thrombotic thrombocytopenic purpura (iTTP) survivors experience high rates of adverse health sequelae and increased mortality over long-term follow-up. We conducted this multicenter cohort study to evaluate long-term mortality and causes of death in iTTP survivors. Between 2003 and 2020, 222 patients were enrolled in the Ohio State University and Johns Hopkins TTP registries and followed for a median of 4.5 (interquartile range [IQR], 75 0.4-11.5) years. Nine patients died during their first iTTP episode, and 29 patients died during follow-up. Mortality rate was 1.8 times higher than expected from an age-, sex-, and race-adjusted reference population. Cardiovascular disease was a leading primary cause of death (27.6%) tied with relapsed iTTP (27.6%), followed by malignancy (20.7%), infection (13.8%), and other causes (10.3%). Male sex (hazard ratio [HR], 3.74; 95% confidence interval [CI], 1.65-8.48), increasing age (HR, 1.04; 95% CI, 1.01-1.07), and number of iTTP episodes (HR, 1.10; 95% CI, 1.01-1.20) were associated with mortality in a model adjusted for African American race (HR, 0.70; 95% CI, 0.30-1.65), hypertension (HR, 0.47; 95% CI, 0.20-1.08), chronic kidney disease (HR 1.46; 95% CI, 0.65-3.30), and site (HR, 1.46; 95% CI, 0.64-3.30). There was a trend toward shorter survival in patients with lower ADAMTS13 activity during remission (P = .078). Our study highlights the need for survivorship care and investigation focused on cardiovascular disease and early mortality in TTP survivors.

Advances in ADAMTS biomarkers

A Disintegrin and Metalloproteinase with Thrombospondin motifs (ADAMTS) are major mediators in extracellular matrix (ECM) turnover and have gained increasing interest over the last years as major players in ECM remodeling during tissue homeostasis and the development of diseases. Although, ADAMTSs are recognized in playing important roles during tissue remodeling, and loss of function in various member of the ADAMTS family could be associated with the development of numerous diseases, limited knowledge is available about their specific substrates and mechanism of action. In this chapter, we will review current knowledge about ADAMTSs and their use as disease biomarkers.

Near-complete vision recovery from bilateral serous retinal detachment associated with thrombotic thrombocytopenic purpura

Ocular manifestations of thrombotic thrombocytopenic purpura (TTP) are uncommon, and bilateral retinal detachment is a rare presentation of TTP. We report a rare case of bilateral retinal detachment from underlying TTP in a patient presenting with vision loss. A 56-year-old man presented with a 4-day history of bilateral vision loss. Bilateral serous retinal detachment was confirmed using dilated ophthalmoscope examination. Laboratory results were significant for severe thrombocytopenia, peripheral smear revealed numerous schistocytes and ADAMTS13 activity of less than 1%. The patient was treated with plasma exchange (PLEX), prednisone, rituximab and caplacizumab. This case report highlights that prompt treatment of TTP with PLEX, prednisone, rituximab and caplacizumab could result in significant vision recovery.

Microlyse: a thrombolytic agent that targets VWF for clearance of microvascular thrombosis

Thrombotic microangiopathies are hallmarked by attacks of disseminated microvascular thrombosis. In thrombotic thrombocytopenic purpura (TTP), this is caused by a rise in thrombogenic ultra-large von Willebrand factor (VWF) multimers because of ADAMTS13 deficiency. We previously reported that systemic plasminogen activation is therapeutic in a TTP mouse model. In contrast to its natural activators (ie, tissue plasminogen activator and urokinase plasminogen activator [uPA]), plasminogen can directly bind to VWF. For optimal efficacy and safety, we aimed to focus and accelerate plasminogen activation at sites of microvascular occlusion. We here describe the development and characterization of Microlyse, a fusion protein consisting of a high-affinity VHH targeting the CT/CK domain of VWF and the protease domain of uPA, for localized plasminogen activation on microthrombi. Microlyse triggers targeted destruction of platelet-VWF complexes by plasmin on activated endothelial cells and in agglutination studies. At equal molar concentrations, Microlyse degrades microthrombi sevenfold more rapidly than blockade of platelet-VWF interactions with a bivalent humanized VHH (caplacizumab*). Finally, Microlyse attenuates thrombocytopenia and tissue damage (reflected by increased plasma lactate dehydrogenase activity, as well as PAI-1 and fibrinogen levels) more efficiently than caplacizumab* in an ADAMTS13-/- mouse model of TTP, without affecting hemostasis in a tail-clip bleeding model. These findings show that targeted thrombolysis of VWF by Microlyse is an effective strategy for the treatment of TTP and might hold value for other forms of VWF-driven thrombotic disease.

Platelet Activation Mechanisms and Consequences of Immune Thrombocytopenia

Autoimmune disorders are often associated with low platelet count or thrombocytopenia. In immune-induced thrombocytopenia (IIT), a common mechanism is increased platelet activity, which can have an increased risk of thrombosis. In addition, or alternatively, auto-antibodies suppress platelet formation or augment platelet clearance. Effects of the auto-antibodies are linked to the unique structural and functional characteristics of platelets. Conversely, prior platelet activation may contribute to the innate and adaptive immune responses. Extensive interplay between platelets, coagulation and complement activation processes may aggravate the pathology. Here, we present an overview of the reported molecular causes and consequences of IIT in the most common forms of autoimmune disorders. These include idiopathic thrombocytopenic purpura (ITP), systemic lupus erythematosus (SLE), antiphospholipid syndrome (APS), drug-induced thrombocytopenia (DITP), heparin-induced thrombocytopenia (HIT), COVID-19 vaccine-induced thrombosis with thrombocytopenia (VITT), thrombotic thrombocytopenia purpura (TTP), and hemolysis, the elevated liver enzymes and low platelet (HELLP) syndrome. We focus on the platelet receptors that bind auto-antibodies, the immune complexes, damage-associated molecular patterns (DAMPs) and complement factors. In addition, we review how circulating platelets serve as a reservoir of immunomodulatory molecules. By this update on the molecular mechanisms and the roles of platelets in the pathogenesis of autoimmune diseases, we highlight platelet-based pathways that can predispose for thrombocytopenia and are linked thrombotic or bleeding events.

Shrinking Weibel-Palade bodies prevents high platelet recruitment in assays using thrombotic thrombocytopenic purpura plasma

BACKGROUND

Thrombotic thrombocytopenic purpura (TTP), caused by a genetic or autoimmune-driven lack of ADAMTS-13 activity, leads to high levels of the ultra-large von Willebrand factor (VWF) multimers produced by endothelial cells, causing excess platelet recruitment into forming thrombi, often with mortal consequences. Treatments include plasma infusion or replacement to restore ADAMTS-13 activity, or prevention of platelet recruitment to VWF.

OBJECTIVES

We tested a different approach, exploiting the unique cell biology of the endothelium. Upon activation, the VWF released by exocytosis of Weibel-Palade bodies (WPBs), transiently anchored to the cell surface, unfurls as strings into flowing plasma, recruiting platelets. Using plasma from patients with TTP increases platelet recruitment to the surface of cultured endothelial cells under flow. WPBs are uniquely plastic, and shortening WPBs dramatically reduces VWF string lengths and the recruitment of platelets. We wished to test whether the TTP plasma-driven increase in platelet recruitment would be countered by reducing formation of the longest WPBs that release longer strings.

METHODS

Endothelial cells grown in flow chambers were treated with fluvastatin, one of 37 drugs shown to shorten WPBs, then activated under flow in the presence of platelets and plasma of either controls or patients with TTP.

RESULT

We found that the dramatic increase in platelet recruitment caused by TTP plasma is entirely countered by treatment with fluvastatin, shortening the WPBs.

CONCLUSIONS

This potential approach of ameliorating the endothelial contribution to thrombotic risk by intervening far upstream of hemostasis might prove a useful adjunct to more conventional and direct therapies.

Shedding Light on the Possible Link between ADAMTS13 and Vaccine-Induced Thrombotic Thrombocytopenia

Several recent reports have highlighted the onset of vaccine-induced thrombotic thrombocytopaenia (VITT) in some recipients (approximately 1 case out of 100k exposures) of the ChAdOx1 nCoV-19 vaccine (AstraZeneca). Although the underlying events leading to this blood-clotting phenomenon has yet to be elucidated, several critical observations present a compelling potential mechanism. Thrombus formation requires the von Willebrand (VWF) protein to be in ultra-large multimeric state. The conservation of this state is controlled by the ADAMTS13 enzyme, whose proteolytic activity reduces the size of VWF multimers, keeping blood clotting at bay. However, ADAMTS13 cannot act on VWF that is bound to platelet factor 4 (PF4). As such, it is of particular interest to note that a common feature between subjects presenting with VITT is high titres of antibodies against PF4. This raises the possibility that these antibodies preserve the stability of ultra-large VWF complexes, leading to the formation of endothelium-anchored VWF strings, which are capable of recruiting circulating platelets and causing uncontrolled thrombosis in terminal capillaries. Here, we share our viewpoint about the current understanding of the VITT pathogenesis involving the prevention of ADAMTS13's activity on VWF by PF4 antibody-mediated stabilisation/ protection of the PF4-VWF complex.

Pathophysiology of Vaccine-Induced Prothrombotic Immune Thrombocytopenia (VIPIT) and Vaccine-Induced Thrombocytopenic Thrombosis (VITT) and Their Diagnostic Approach in Emergency

SARS-CoV-2 induced a pandemic that is reported to have started in Asia and was then extended to other countries in the world. Main clinical aspects of this viral infection have been lung injuries with severe pneumonia requiring prolonged hospitalization and associated morbidities such as venous thromboembolism and/or superinfection by bacteria, fungus or other pests. Immediately there was a need to develop a sustainable therapeutic strategy, such as vaccination. Vaccines against Covid-19, in fact, exert a protective action for common people and reduce viral diffusion. Yet, vaccination of a large number of people raises the question of a well-known complication of several types of vaccines; this complication is immune thrombocytopenia, which is sometimes associated with thrombosis as well. In this short review, we summarized mechanisms involved in the pathogenesis of vaccine-induced prothrombotic immune thrombocytopenia and vaccine-induced thrombocytopenic thrombosis.

Age-Associated Increase in Thrombogenicity and Its Correlation with von Willebrand Factor

Endothelial cells that cover the lumen of all blood vessels have the inherent capacity to express both pro and anticoagulant molecules. However, under normal physiological condition, they generally function to maintain a non-thrombogenic surface for unobstructed blood flow. In response to injury, certain stimuli, or as a result of dysfunction, endothelial cells release a highly adhesive procoagulant protein, von Willebrand factor (VWF), which plays a central role in formation of platelet aggregates and thrombus generation. Since VWF expression is highly restricted to endothelial cells, regulation of its levels is among the most important functions of endothelial cells for maintaining hemostasis. However, with aging, there is a significant increase in VWF levels, which is concomitant with a significant rise in thrombotic events. It is not yet clear why and how aging results in increased VWF levels. In this review, we have aimed to discuss the age-related increase in VWF, its potential mechanisms, and associated coagulopathies as probable consequences.

Evaluation and Management of Thrombotic Thrombocytopenic Purpura in the Emergency Department

BACKGROUND

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

OBJECTIVE

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

DISCUSSION

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

CONCLUSION

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

Characterization of the interactions of ADAMTS13 CUB1 domain to WT- and GOF-Spacer domain by molecular dynamics simulation

Metalloprotease ADAMTS13 specifically cleaves VWF (von Willebrand Factor) to prevent excessive platelet aggregation and thrombus formation at the sites of vascular injury. To avoid non-specific cleavage, ADAMTS13 has the auto-inhibition effect in which the Spacer domain in N-terminal interacts with the CUB1 domain in C-terminal, resulting in decreased proteolytic activity. Previous studies reported that exosite-3 in the Spacer domain was a key binding site in the Spacer-CUB1 interaction. When exosite-3 was mutated (R660K/F592Y/R568K/Y661F/Y665F, GOF), the auto-inhibition of ADAMTS13 was disrupted and the enzymatic activity was markedly increased. However, the characteristics of the Spacer-CUB1 interaction is not fully understood. Here, we constructed the model of Spacer-CUB1 complex by homologous modeling and molecular docking to characterize the Spacer-CUB1 binding and predict key amino acid residues via molecular dynamics simulation. Our data showed that G607-S610 was a non-reported potential binding site in the Spacer domain; GOF mutation attenuated the formation of hydrogen bond between exosite-3 and the CUB1 domain; Residues E1231, R1251, L1258, D1259 and T1261 in the CUB1 domain might play an important role in the Spacer-CUB1 interaction. Our study advances the understanding of the structural basis of the auto-inhibition of ADAMTS13 and provides information about the key residues in the binding interface.

Influence of Vincristine, Clinically Used in Cancer Therapy and Immune Thrombocytopenia, on the Function of Human Platelets

Vincristine is a clinically used antimicrotubule drug for treating patients with lymphoma. Due to its property of increasing platelet counts, vincristine is also used to treat patients with immune thrombocytopenia. Moreover, antiplatelet agents were reported to be beneficial in thrombotic thrombocytopenic purpura (TTP). Therefore, we investigated the detailed mechanisms underlying the antiplatelet effect of vincristine. Our results revealed that vincristine inhibited platelet aggregation induced by collagen, but not by thrombin, arachidonic acid, and the thromboxane A₂ analog U46619, suggesting that vincristine exerts higher inhibitory effects on collagen-mediated platelet aggregation. Vincristine also reduced collagen-mediated platelet granule release and calcium mobilization. In addition, vincristine inhibited glycoprotein VI (GPVI) signaling, including Syk, phospholipase Cγ2, protein kinase C, Akt, and mitogen-activated protein kinases. In addition, the in vitro PFA-100 assay revealed that vincristine did not prolong the closure time, and the in vivo study tail bleeding assay showed that vincristine did not prolong the tail bleeding time; both findings suggested that vincristine may not affect normal hemostasis. In conclusion, we demonstrated that vincristine exerts antiplatelet effects at least in part through the suppression of GPVI signaling. Moreover, this property of antiplatelet activity of vincristine may provide additional benefits in the treatment of TTP.

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

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

Sudden coma at the onset of severe refractory thrombotic thrombocytopenic purpura with successful treatment

Most patients develop coma several days after the onset of thrombotic thrombocytopenic purpura (TTP) caused by microvascular occlusion. However, aggravated coma as the first symptom of TTP has rarely been reported. Although plasma exchange (PEX) and steroids have reduced mortality, the prognosis of patients with TTP is still poor. We reported a patient with refractory TTP presenting with aggravated coma on admission. After days of successful PEX, rituximab, and glucocorticoid therapy for clinical remission, the patient regained consciousness and returned to his normal life with a good outcome. Our case highlights that TTP should be considered when coma occurs as the first symptom.

Snakebite-associated thrombotic microangiopathy: an Australian prospective cohort study [ASP30]

BACKGROUND

Snakebite-associated thrombotic microangiopathy (TMA) occurs in a subset of patients with venom-induced consumption coagulopathy (VICC) following snakebite. Acute kidney injury (AKI) is the commonest end-organ manifestation of TMA. The epidemiology, diagnostic features, outcomes, and effectiveness of interventions including therapeutic plasma-exchange (TPE), in snakebite-associated TMA are poorly understood.

METHODS

We reviewed all patients with suspected or confirmed snakebite recruited to the Australian Snakebite Project (2004-2018 inclusive), a prospective cohort study, from 202 participating Australian hospitals across the country. TMA was defined as anemia with schistocytosis.

RESULTS

2069 patients with suspected snakebite were enrolled, with 1158 (56.0%) systemically envenomed, of which 842 (72.7%) developed VICC, from which 104 (12.4%) developed TMA. Of those systemically envenomed, TMA occurred in 26% (13/50) taipan, 17% (60/351) brown, and 8% (16/197) tiger snakebites. Thrombocytopenia was present in 90% (94/104) of TMA cases, and a further eight (8%) had a > 25% decrease in platelets from the presentation. Patients with TMA were significantly older than non-TMA patients with VICC (53 [35-61] versus 41 [24-55] years, median [IQR], p < 0.0001). AKI developed in 94% (98/104) of TMA patients, with 34% (33/98) requiring dialysis (D-AKI). There were four deaths. In D-AKI TMA cases, eventual dialysis-free survival (DFS) was 97% (32/33). TPE was used in five D-AKI cases, with no significant difference in DFS or time to independence from dialysis. >90-day follow-up for 25 D-AKI cases (130 person-years) showed no end-stage kidney disease but 52% (13/25) had ≥ stage 3 chronic kidney disease (CKD).

CONCLUSION

Our findings support a definition of snakebite-associated TMA as anemia with schistocytosis and either thrombocytopenia or >25% drop in platelet count. AKI occurring with snakebite-associated TMA varied in severity, with most achieving DFS, but with a risk of long-term CKD in half. We found no evidence of benefit for TPE in D-AKI.

Strong association between insufficient plasma exchange and fatal outcomes in Japanese patients with immune-mediated thrombotic thrombocytopenic purpura

Plasma exchange (PEX) using fresh frozen plasma has considerably reduced the mortality rate in patients with immune-mediated thrombotic thrombocytopenic purpura (iTTP). However, some patients still do not survive even with treatment, but little information is available regarding which treatment these patients received. This study was conducted to obtain this information in 240 patients who met the current iTTP diagnostic criteria and completed at least 30 days of follow-up except for deceased cases. These patients were divided into three groups: survivors (n = 195), TTP-related deaths (n = 32), and other cause of death (n = 13). In the TTP-related death group, 26 of 32 patients experienced sudden death, mostly following radical hypotension and bradycardia. The median follow-up time after admission was 5.0 days, and the median number of PEX sessions was 2.5. Nine patients underwent autopsy and had cardiac microvascular thrombi in arterioles. Levels of lactate dehydrogenase, total bilirubin, serum creatinine, and D-dimer were significantly higher in the TTP-related death group than in the survivors group. Frequent PEX (> 20 sessions) was not associated with TTP-related death. In the acute phase of iTTP, patients with substantial organ damage caused by microthrombi have a greater mortality risk, even after just a few PEX sessions.

Pro-coagulant imbalance in patients with community acquired pneumonia assessed on admission and one month after hospital discharge

OBJECTIVES

Patients hospitalized because of community-acquired-pneumonia (CAP) are at risk of cardiovascular diseases. Although plasma procoagulant imbalance play a role, mechanisms are not completely understood. We aimed to investigate whether there is a measurable state of procoagulant imbalance following inflammation determined by CAP.

METHODS

We analyzed blood from 51 CAP patients at admission and 51 healthy subjects (HS) for (i) pro and anticoagulants, (ii) thrombin generation (TG) with or without thrombomodulin (TM), which is the physiologic activator of the protein C anticoagulant pathway and(iii) by assessing the ratio between von Willebrand-factor (VWF) and its protease ADAMTS13. Thirty patients were re-analyzed one month after discharge when CAP was resolved.

RESULTS

Median levels of TG parameters, including the endogenous thrombin potential (ETP), the ETP-TM-ratio (with/without TM), peak-thrombin and velocity index were higher in patients at baseline than HS. In particular, the median (IQR) ETP-TM-ratio in patients vs. HS was 0.88 (0.83-0.91) vs. 0.63 (0.48-0.71), p<0.001. Factor (F)VIII, a potent procoagulant involved in TG was higher in patients at baseline than HS [195 U/dL (100-388) vs. 127(108-145)], p<0.001]. The ratio of VWF/ADAMTS13 was higher at baseline than HS. Cumulatively, the findings indicate a state of pro-coagulant imbalance, which (although reduced), remained high [i.e., ETP-TM-ratio, 0.80 (0.74-0.84); FVIII, 152 U/dL (122-190)] one month after discharge when the infection was resolved.

CONCLUSIONS

Patients with CAP possess a state of pro-coagulant imbalance, which remains substantially high, even when the infection is resolved. The findings suggest CAP patients as candidates for antithrombotic prophylaxis even after the resolution of infection. Clinical trials are warranted to assess the benefit/risk ratio of prophylaxis extension.

Acquired Thrombotic Thrombocytopenic Purpura in a Newly Diagnosed HIV Patient: A Case Report and Literature Review

Thrombotic thrombocytopenic purpura (TTP) is a rare but a potentially fatal condition. Although the majority of TTP cases are of unknown etiology, certain viral infections, malignancies, and medications have been linked to the acquired form of the illness. Regardless of the underlying etiology, TTP remains a great challenge diagnostically and therapeutically. TTP remains a very uncommon complication of HIV. We reviewed the current literature to better understand the relationship between HIV and TTP and address some of the major obstacles that may impede or delay the correct diagnosis. Here, we present a case of a 28-year-old male with complaints of light-headedness, fatigue, and gingival bleeding. He was found to have severe anemia and thrombocytopenia. He tested positive for the HIV and was then diagnosed with TTP. Despite needing endotracheal intubation for airway protection, he clinically improved with packed red blood cells, plasmapheresis, and highly active antiretroviral therapy.

Annual incidence and severity of acute episodes in hereditary thrombotic thrombocytopenic purpura

Hereditary thrombotic thrombocytopenic purpura (hTTP) is a rare thrombotic microangiopathy characterized by severe congenital ADAMTS13 deficiency and recurring acute episodes causing morbidity and premature death. Information on the annual incidence and severity of acute episodes in patients with hTTP is largely lacking. This study reports prospective data on 87 patients from the Hereditary TTP Registry (clinicaltrials.gov #NCT01257269) for survival, frequency, and severity of acute episodes from enrollment until December 2019. The 87 patients, followed up for a median of 4.2 years (range, 0.01-15 years), had a median age at overt disease onset and at clinical diagnosis of 4.6 years and 18 years (range, 0.0-70 years for both), respectively. Forty-three patients received regular plasma prophylaxis, whereas 22 did not, and treatment changed over time or was unknown in the remaining 22. Forty-three patients experienced 131 acute episodes, of which 91 (69%) occurred in patients receiving regular prophylaxis. This resulted in an annual incidence of acute episodes of 0.36 (95% confidence interval [CI], 0.29-0.44) with regular plasma treatment and of 0.41 (95% CI, 0.30-0.56) without regular plasma treatment. More than one-third of acute episodes (n = 51) were documented in children <10 years of age at enrollment and were often triggered by infections. Their annual incidence of acute episodes was significantly higher than in patients aged >40 years (1.18 [95% CI, 0.88-1.55] vs 0.14 [95% CI, 0.08-0.23]). The prophylactic plasma infusion regimens used were insufficient to prevent acute episodes in many patients. Such regimens are burdensome, and caregivers, patients, and their guardians are reluctant to start regular plasma infusions, from which children particularly would benefit.

A Novel Case of Leflunomide-Induced Thrombotic Thrombocytopenic Purpura

Leflunomide has not been previously associated with thrombotic thrombocytopenic purpura (TTP), a rare life-threatening clinical syndrome characterized by thrombotic microangiopathy (TMA) due to inability to cleave ADAMTS13. Here, we present the first case of leflunomide-induced TTP. Our patient developed encephalopathy, thrombocytopenia, anemia and hyperbilirubinemia 2 months after starting leflunomide. Schistocytes were noted on peripheral smear and ADAMTS13 activity was low (< 5%), consistent with acquired TTP. He received therapeutic plasma exchange, corticosteroids, rituximab and caplacizumab with normalization of hemolysis labs and ADAMTS13 activity. However, pancytopenia persisted, raising the suspicion for leflunomide toxicity. Oral cholestyramine treatment was empirically started before teriflunomide (a leflunomide metabolite) level was found to be elevated. Blood counts normalized after cholestyramine and have remained normal at last follow-up over a year later. This is the first reported case of TTP precipitated by leflunomide. Our case highlights the importance of recognizing drugs as an etiology of TMA and adds leflunomide to this list.

[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.

Unresponsive Thrombotic Thrombocytopenic Purpura (TTP): Challenges and Solutions

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

Current prophylactic plasma infusion protocols do not adequately prevent long-term cumulative organ damage in the Japanese congenital thrombotic thrombocytopenic purpura cohort

Congenital thrombotic thrombocytopenic purpura (cTTP), known as Upshaw-Schulman syndrome, is an ultrarare thrombotic disorder caused by ADAMTS13 gene mutations; however, its long-term outcomes have not been widely studied. A questionnaire survey was administered to physicians of patients in the Japanese cTTP registry to characterise these outcomes. We analysed 55 patients in remission, with 41 cases receiving prophylactic fresh frozen plasma (FFP; median dosage: 13·2 ml/kg per month) and 14 receiving on-demand FFP. Patients receiving prophylactic FFP were considered as having a more severe form of the disease and had lower platelet counts and higher serum creatinine levels than those receiving on-demand FFP (median 138 × 10⁹ /l vs. 243 × 10⁹ /l, P = 0·003 and 0·71 mg/dl vs 0·58 mg/dl, P = 0·009, respectively). Patients who received prophylactic FFP more commonly developed organ damage, including renal impairment, cerebral infarctions, and cardiac hypofunction, than those who did not. Adverse FFP-related events were seen in 78% of the prophylactic FFP group, with allergic reactions being most common. Since current protocols for FFP administration to the prophylactic FFP group in Japan may be insufficient for preventing cumulative organ damage, a higher dosage of ADAMTS13 supply using recombinant ADAMTS13 agent is needed in these patients.

Rituximab leads to early elimination of circulating CD20+ T and B lymphocytes in patients with iTTP despite ongoing TPEx

How TPEx impacts rituximab effectiveness in iTTP patients is not fully understood. In iTTP patients on therapeutic plasma exchange, rituximab eliminates circulating CD20+ B and T cells in 24 hours for at least 1 week.

An evaluation of existing manual blood film schistocyte quantitation guidelines and a new proposed method

Schistocytosis is the morphological hallmark of the microangiopathic haemolytic anaemia of thrombotic microangiopathy (TMA). Consensus guidelines for manual schistocyte quantitation are available, but limited research has evaluated them. The 2012 International Council for Standardization in Haematology (ICSH) recommends a schistocyte quantitation of 1% as a robust cut-off for significance, with the quantitation including helmet, crescent, triangle and keratocyte poikilocytes; and microspherocytes only in the presence of helmets, crescents/triangles, and keratocytes. We aimed to evaluate the relative contribution of these different poikilocytes to schistocyte counting; compare the ICSH method with our proposed method which counts only cells most specific for red cell fragmentation (helmet, crescent and triangular schistocytes); and evaluate inter- and intra-observer agreement. Blood films were sourced from the Australian Snakebite Project, including non-envenomed and envenomed cases, with and without TMA. In blood films across the range of schistocytosis, the predominant poikilocytes present were helmets and crescents. Triangles, keratocytes and microspherocytes were typically only present when ICSH schistocyte count was >1%. With results dichotomised as <1.0% or ≥1.0%, our proposed new method versus the ICSH method showed almost perfect agreement [observed agreement 95%, Cohen's kappa (κ)=0.84, SE 0.04, 95% CI 0.76-0.92, p<0.005]. Inter-observer strength of agreement for our method was moderate (Fleiss' κ for comparisons between three non-unique microscopists κ=0.50, SE 0.05, 95% CI 0.41-0.59, p<0.005). Intra-observer reproducibility assessed in two microscopists ranged from substantial (Cohen's κ=0.71, SE 0.08, 95% CI 0.55-0.86, p<0.005) to borderline almost perfect agreement (Cohen's κ=0.81, SE 0.07, 95% CI 0.68-0.93, p<0.005). Schistocyte quantitation using our new method is simpler than the 2012 ICSH method and had almost perfect agreement. Our finding of moderate inter-observer agreement in quantitating helmet, triangle and crescent schistocytes is applicable to both the ICSH and our newly proposed method. This finding underscores the importance of clinicopathological correlation and repeated examinations in the context of a clinically suspected TMA.

A Case of Thrombotic Thrombocytopenic Purpura without Pathognomonic Schistocytes

Patients diagnosed with thrombotic thrombocytopenic purpura (TTP) typically present with microangiopathic hemolytic anemia (MAHA) and thrombocytopenia; these two clinical manifestations were often believed to be essential indicators of TTP. However, such indicators are not always present in every case. Here, we present a patient affected by TTP but showing no distinctive schistocytes on blood smear review. TTP was diagnosed through a critically low level of a disintegrin and metalloproteinase with thrombospondin type 1 motif, member 13 (ADAMTS13) activity. Awareness of such an atypical presentation of TTP is essential for timely treatment to prevent serious and even fatal outcomes for patients.

Educational Case: Differentiating Thrombotic Thrombocytopenic Purpura From Other Thrombotic Microangiopathies and Potential Role of the Spleen

The following fictional case is intended as a learning tool within the Pathology Competencies for Medical Education (PCME), a set of national standards for teaching pathology. These are divided into three basic competencies: Disease Mechanisms and Processes, Organ System Pathology, and Diagnostic Medicine and Therapeutic Pathology. For additional information, and a full list of learning objectives for all three competencies, seehttp://journals.sagepub.com/doi/10.1177/2374289517715040.¹