Thrombotic Thrombocytopenic Purpura-Then and Now

Unmet needs in the management of immune-mediated thrombotic thrombocytopenic purpura and the potential role of caplacizumab in the UK-A modified-Delphi study

Immune-mediated thrombotic thrombocytopenic purpura (iTTP) is an ultra-rare, blood-clotting disorder. Management historically relies on plasma exchange and immunosuppression; however, a 10%-20% mortality rate is still observed. Caplacizumab binds to von Willebrand factor and directly inhibits platelet aggregation; addition of caplacizumab to historical treatment induced faster resolution of platelet count in clinical trials. In 2019, a modified-Delphi study was conducted with UK experts, to develop consensus statements on management of acute TTP and the potential role of caplacizumab. An unmet need was acknowledged, and areas requiring improvement included: time to diagnosis and treatment initiation; time to platelet normalisation (TTPN) during which patients remain at risk of persistent microvascular thrombosis and organ damage; and incidence of subsequent exacerbations and relapses. Caplacizumab addition to historical treatment within 24 h (after confirmatory ADAMTS13 [a disintegrin and metalloproteinase with thrombospondin type 1 motif, member 13] assay) would significantly reduce TTPN, which directly influences acute outcomes, with manageable bleeding risk and reduced burden on healthcare systems. Expert panellists agree that poor outcomes in iTTP largely result from failure to rapidly control microvascular thrombosis. Use of caplacizumab during a confirmed iTTP episode could offer better control and may plausibly improve long-term outcomes. However, this consensus must be validated with further clinical trials and robust real-world evidence.

Disseminated intravascular coagulation: new identity as endotheliopathy-associated vascular microthrombotic disease based on in vivo hemostasis and endothelial molecular pathogenesis

Disseminated intravascular coagulation (DIC) can be correctly redefined as disseminated intravascular microthrombosis based on "two-path unifying theory" of in vivo hemostasis. "DIC" is a form of vascular microthrombotic disease characterized by "microthrombi" composed of platelets and unusually large von Willebrand factor multimers (ULVWF). Microthrombotic disease includes not only "DIC", but also microthrombosis occurring in thrombotic thrombocytopenic purpura (TTP), TTP-like syndrome, and focal, multifocal and localized microthrombosis. Being a hemostatic disease, microthrombotic disease occurs as a result of lone activation of ULVWF path via partial in vivo hemostasis. In endothelial injury associated with critical illnesses such as sepsis, the vascular damage is limited to the endothelial cell and activates ULVWF path. In contrast, in intravascular traumatic injury, the local damage may extend from the endothelial cell to subendothelial tissue and sometimes beyond, and activates both ULVWF and tissue factor (TF) paths. When endotheliopathy triggers exocytosis of ULVWF and recruits platelets, ULVWF path is activated and promotes microthrombogenesis to produce microthrombi composed of microthrombi strings, but when localized vascular damage causes endothelial and subendothelial tissue damage, both ULVWF and TF paths are activated and promote macrothrombogenesis to produce macrothrombus made of complete "blood clots". Currently, "DIC" concept is ascribed to activated TF path leading to fibrin clots. Instead, it should be correctly redefined as microthrombosis caused by activation of ULVWF path, leading to endotheliopathy-associated microthrombosis. The correct term for acute "DIC" is disseminated microthrombosis-associated hepatic coagulopathy, and that for chronic "DIC" is disseminated microthrombosis without hepatic coagulopathy. TTP-like syndrome is hematologic phenotype of endotheliopathy-associated microthrombosis. This correct concept of "DIC" is identified from novel theory of "in vivo hemostasis", which now can solve every mystery associated with "DIC" and other associated thrombotic disorders. Thus, sepsis-associated coagulopathy is not "DIC", but is endotheliopathy-associated vascular microthrombotic disease.

Atypical Hemolytic Uremic Syndrome Presenting as Acute Heart Failure-A Rare Presentation: Diagnosis Supported by Skin Biopsy

Atypical hemolytic uremic syndrome (aHUS) is a rare disorder of uncontrolled complement activation that manifests classically as anemia, thrombocytopenia, and renal failure, although extrarenal manifestations are observed in 20% of the patient most of which involving central nervous system, with relatively rare involvement of the heart. In this article, we report the case of a 24-year-old male with no history of heart disease presenting with acute systolic heart failure along with microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury. Given his presentation of thrombotic microangiopathy (TMA), along with laboratory results significant for low haptoglobin, platelets, hemoglobin, C3, C4, CH50, and normal ADAMTS13 levels, with no diarrhea and negative STEC polymerase chain reaction in stool, aHUS diagnosis was established with strong clinical suspicion, and immediate initiation of treatment was advised. Kidney biopsy to confirm diagnosis of aHUS was inadvisable because of thrombocytopenia, so the skin biopsy of a rash on his arm was done, which came to be consistent with thrombotic microangiopathy. Our case highlights a relatively rare association between aHUS and cardiac involvement, and the use of skin biopsy to support diagnosis of aHUS in patients who cannot undergo renal biopsy because of thrombocytopenia.

A STARD-compliant prediction model for diagnosing thrombotic microangiopathies

Aim of the study was the definition of a predictive model for the initial diagnosis of thrombotic microangiopathies (TMA). We retrospectively collected data on all adult patients admitted to the Gemelli Hospital from 2010 to 2014. ICD-9 codes from primary diagnoses were used for TMA diagnosis. Demographic and laboratory characteristics on admission of patients with TMA were then compared with a random sample of 500 patients with other diagnoses. The prediction model was externally validated in a cohort from another hospital. Overall, 23 of 187,183 patients admitted during the study period received a primary diagnosis of TMA. LDH (OR 1.26, 95% CI 1.05, 1.63) and platelets (OR 0.96, 95% CI 0.94, 0.98) were the only independent predictors of TMA. The AUROC of the final model including only LDH and platelets was 0.96 (95% CI 0.91, 1.00). The Hosmer-Lemeshow (HL) test (p = 0.54) suggested good calibration. Our model also confirmed good discriminatory power (AUROC 0.72 95% CI 0.60, 0.84) and calibration (HL test p = 0.52) in the validation sample. We present a simple prediction model for use in diagnosing TMA in hospitalized patients. The model performs well and can help clinicians to identify patients at high risk of TMA.

Presenting ADAMTS13 antibody and antigen levels predict prognosis in immune-mediated thrombotic thrombocytopenic purpura

Immune-mediated thrombotic thrombocytopenic purpura (TTP) is a life-threatening disorder caused by antibodies against ADAMTS13. From the United Kingdom TTP registry, we undertook a prospective study investigating the impact of the presenting anti-ADAMTS13 IgG antibody and ADAMTS13 antigen on mortality. A total of 312 episodes involving 292 patients over 87 months were included; 68% were female, median age 46 (range, 11-88 years), and median presenting ADAMTS13 of <5% (range, <5%-18%). The mortality rate was 10.3% (n = 32); 68% of patients had a raised troponin at presentation conferring a sixfold increase in mortality compared with those with normal troponin levels (12.1% vs 2.0%, P = .04). Twenty-four percent had a reduced Glasgow Coma Score (GCS) at presentation with a ninefold increase in mortality (20% vs 2.2% for normal GCS at presentation, P < .0001). Mortality increased with higher anti-ADAMTS13 antibody levels and lower ADAMTS13 antigen levels. Those with antibody levels in the upper quartile (antibody >77%) had a mortality of 16.9% compared with 5.0% for the lowest quartile (antibody <20%) (P = .004). Those with an antigen level in the lowest quartile (antigen <1.5%) had a mortality of 18% compared with 3.8% for the highest quartile (antigen >11%) (P = .005). The synergistic effect of anti-ADAMTS13 IgG antibody in the upper quartile and ADAMTS13 antigen in the lowest quartile had the highest mortality of 27.3%. We conclude that both anti-ADAMTS13 IgG antibody and ADAMTS13 antigen levels correlate with outcome in TTP with increased cardiac and neurological involvement and increased mortality.

Interaction between Multimeric von Willebrand Factor and Complement: A Fresh Look to the Pathophysiology of Microvascular Thrombosis

von Willebrand factor (VWF), a multimeric protein with a central role in hemostasis, has been shown to interact with complement components. However, results are contrasting and inconclusive. By studying 20 patients with congenital thrombotic thrombocytopenic purpura (cTTP) who cannot cleave VWF multimers because of genetic ADAMTS13 deficiency, we investigated the mechanism through which VWF modulates complement and its pathophysiological implications for human diseases. Using assays of ex vivo serum-induced C3 and C5b-9 deposits on endothelial cells, we documented that in cTTP, complement is activated via the alternative pathway (AP) on the cell surface. This abnormality was corrected by restoring ADAMTS13 activity in cTTP serum, which prevented VWF multimer accumulation on endothelial cells, or by an anti-VWF Ab. In mechanistic studies we found that VWF interacts with C3b through its three type A domains and initiates AP activation, although assembly of active C5 convertase and formation of the terminal complement products C5a and C5b-9 occur only on the VWF-A2 domain. Finally, we documented that in the condition of ADAMTS13 deficiency, VWF-mediated formation of terminal complement products, particularly C5a, alters the endothelial antithrombogenic properties and induces microvascular thrombosis in a perfusion system. Altogether, the results demonstrated that VWF provides a platform for the activation of the AP of complement, which profoundly alters the phenotype of microvascular endothelial cells. These findings link hemostasis-thrombosis with the AP of complement and open new therapeutic perspectives in cTTP and in general in thrombotic and inflammatory disorders associated with endothelium perturbation, VWF release, and complement activation.

The Differential Diagnosis of Thrombocytopenia in Pregnancy

BACKGROUND

Thrombocytopenia is, after anemia, the second most common abnormality of the complete blood count in pregnancy, with a reported frequency of 6.6% to 11.2%. It has many causes. Thrombocytopenia should be diagnostically evaluated as early as possible in pregnancy, so that the obstetrical management can be accordingly planned to minimize harm to the mother and child. As the various underlying diseases share clinical features and laboratory findings, the differential diagnosis is often a difficult interdisciplinary challenge.

METHODS

In this article, we review pertinent literature (2000-January 2015) retrieved by a selective search in PubMed.

RESULTS

Gestational thrombocytopenia is the most common type, accounting for 75% of cases, followed by severe pre-eclampsia/HELLP syndrome (hemolysis, elevated liver enzymes, low platelet count) in 15-22% and autoimmune thrombocytopenia (ITP) in 1-4%. Gestational thrombocytopenia and ITP differ in the bleeding history, the severity of thrombocytopenia, the frequency of neo - natal thrombocytopenia, and the rate of normalization of the platelet count after delivery. The HELLP syndrome and rarer microangiopathic hemolytic anemias (e.g., thrombotic thrombocytopenic purpura) can be differentiated on the basis of their main clinical features, such as hypertension/proteinuria and upper abdominal pain, the severity of hemolysis and thrombocytopenia, the degree of transaminase elevation, and the rapidity of postpartum remission of the clinical and laboratory findings. A stepwise diagnostic procedure should be followed to distinguish further causes, e.g., to differentiate thrombocytopenia due to infection, autoimmune disease, or drugs from thrombocytopenia due to a rare hereditary disease.

CONCLUSION

The early interdisciplinary evaluation of thrombocytopenia in pregnancy is a prerequisite for the optimal care of the mother and child. The development of evidence-based recommendations for interdisciplinary management should be a goal for the near future.

Treatment of Congenital Thrombotic Thrombocytopenic Purpura With Eculizumab

A 12-year-old boy was hospitalized for hemolytic anemia, thrombocytopenia, acute kidney injury, and generalized seizures. The childhood onset, severely decreased kidney function, absence of prodromal diarrhea, negative test results for Shiga-like toxin-producing Escherichia coli, elevated plasma levels of the terminal complement complex sC5b-9, and ex vivo testing in endothelial cells showing serum-induced complement activation were all consistent with a diagnosis of complement-mediated atypical hemolytic uremic syndrome. Before plasma ADAMTS13 (von Willebrand factor protease) activity results were available, the patient was treated with the anti-C5 monoclonal antibody eculizumab, and treatment was followed by prompt disease remission. However, results of ADAMT13 activity level tests and gene screening revealed a severe deficiency associated with 2 heterozygous mutations in the ADAMTS13 gene, fully consistent with a diagnosis of congenital thrombotic thrombocytopenic purpura. Screening for atypical hemolytic uremic syndrome-associated genes failed to show a mutation and an assay for plasma anti-factor H antibodies gave negative results both before and after eculizumab treatment initiation. The patient's clinical evolution suggests that complement activation plays a role in the pathogenesis of thrombotic thrombocytopenic purpura and provides unexpected new insights into the treatment of this life-threatening disease.

ADAMTS13 Secretion and Residual Activity among Patients with Congenital Thrombotic Thrombocytopenic Purpura with and without Renal Impairment

BACKGROUND AND OBJECTIVES

Acute renal impairment is observed in 11%-23% of patients with congenital thrombotic thrombocytopenic purpura (TTP) and deficiency of a disintegrin and metalloprotease with thrombospondin motifs 13 (ADAMTS13, a metalloprotease that cleaves von Willebrand factor [VWF] multimers), a substantial percentage of whom develop CKD during follow-up.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Here we investigated whether, in 18 patients with congenital recruited from 1996 to 2013 who fulfilled inclusion criteria, acute renal involvement occurred during bouts segregated with lower secretion and activity levels of ADAMTS13 mutants. We performed expression studies and a sensitive recombinant VWF (rVWF) A1-A2-A3 cleavage test (detection limit, 0.78% of normal ADAMTS13 activity).

RESULTS

A higher risk of acute renal impairment during bouts was observed in patients with childhood (<18 years) onset (odds ratio [OR], 24.6 [95% confidence interval (CI), 1.11 to 542.44]) or a relapsing (≥1 episode per year) disease (OR, 54.6 [95% CI, 2.25 to 1326.28]) than in patients with adulthood onset or long-lasting remission, respectively. Whatever the age at onset, patients with acute renal impairment had mutations different from those in patients without renal involvement. Moreover, mutations in patients with acute renal impairment compared with those in patients without renal involvement caused lower in vitro rADAMTS13 secretion (1.33% versus 12.5%; P<0.001) and residual activity (0.11% versus 3.47%; P=0.003). rADAMTS13 secretion ≤3.75% and residual activity ≤0.4% best discriminated patients with renal impairment (receiver-operating characteristic curve sensitivity, 100% and 100%; specificity, 100% and 83.3%, respectively; logistic regression OR, 325 [95% CI, 6 to 18339] and 91.7 [95% CI, 3.2 to 2623.5], respectively). All mutations found in patients with childhood onset or relapsing disease were associated with acute renal impairment during bouts, confirming the link between acute renal impairment and early onset or a relapsing course. ADAMTS13 activity levels in vivo, measured in patients' serum by rVWF A1-A2-A3 cleavage test, correlated with in vitro rADAMTS13 mutant activity (r=0.95; P<0.001).

CONCLUSIONS

In congenital TTP, renal impairment and relapsing disease might be predicted by measurements of in vitro rADAMTS13 secretion and activity levels and in vivo serum ADAMTS13 activity.

Thrombotic thrombocytopenic purpura with concomitant small- and large-vessel thrombosis, atypical posterior reversible encephalopathy syndrome and cerebral microbleeds

We report a case of thrombotic thrombocytopenic purpura (TTP) with uncommon imaging features, namely concomitant small- and large-vessel thrombosis, atypical locations of posterior reversible encephalopathy syndrome (PRES) and microbleeds. A 58-year-old Chinese woman presented with slurred speech and multiple petechiae over lower limbs. Blood tests showed thrombocytopenia. Neuroimaging showed multiple acute small infarcts and PRES in the subcortical white matter, basal ganglia, thalamus, brainstem and occipital lobe. Microbleeds were noted. She was treated as TTP with infusion of cryo-reduced plasma (CRP). Patient subsequently developed dense right hemiplegia. Computed tomography of brain demonstrated a new major left middle cerebral artery territory infarct. She was stabilized after 2 weeks of treatment with daily CRP infusion, then received rehabilitation for major stroke. Early recognition of TTP provides the best chance of recovery as most lesions are reversible when TTP was treated. However, concurrent large artery thrombosis could cause major morbidity and mortality.

ADAMTS-13 in the Diagnosis and Management of Thrombotic Microangiopathies

Thrombotic microangiopathies (TMAs) comprise a group of distinct disorders characterized by microangiopathic hemolytic anemia, thrombocytopenia, and microvascular thrombosis. For many years distinction between these TMAs, especially between thrombotic thrombocytopenic purpura (TTP) and hemolytic uremic syndrome (HUS), remained purely clinical and hard to make. Recent discoveries shed light on different pathogenesis of TTP and HUS. Ultra-large von Willebrand factor (UL-VWF) platelet thrombi, resulting from the deficiency of cleavage protease which is now known as ADAMTS-13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13), were found to cause TTP pathology, while Shiga toxins or abnormalities in regulation of the complement system cause microangiopathy and thrombosis in HUS. TMAs may appear in various conditions such as pregnancy, inflammation, malignancy, or exposure to drugs. These conditions might cause acquired TTP, HUS, or other TMAs, or might be a trigger in individuals with genetic predisposition to ADAMTS-13 or complement factor H deficiency. Differentiation between these TMAs is highly important for urgent initiation of appropriate therapy. Measurement of ADAMTS-13 activity and anti-ADAMTS-13 antibody levels may advance this differentiation resulting in accurate diagnosis. Additionally, assessment of ADAMTS-13 levels can be a tool for monitoring treatment efficacy and relapse risk, allowing consideration of therapy addition or change. In the past few years, great improvements in ADAMTS-13 assays have been made, and tests with increased sensitivity, specificity, reproducibility, and shorter turnaround time are now available. These new assays enable ADAMTS-13 measurement in routine clinical diagnostic laboratories, which may ultimately result in improvement of TMA management.

Safety and efficacy of cryoprecipitate-poor plasma as a replacement fluid for therapeutic plasma exchange in thrombotic thrombocytopenic purpura: a single center retrospective evaluation

INTRODUCTION

Thrombotic thrombocytopenic purpura (TTP) is a thrombotic microangiopathy caused by decreased activity of ADAMTS13, resulting in reduced clearance of ultralarge von Willebrand factor (VWF) multimers. Treatment of TTP is therapeutic plasma exchange (TPE) with replacement with fresh frozen plasma (FFP). Cryoprecipitate-poor plasma (CPP) is a plasma product with lower concentrations of large VWF multimers, and similar amounts of ADAMTS13. CPP is regarded as at least as efficacious as FFP in TTP but evidence of additional benefits has not been demonstrated. Furthermore, there are limited data on the frequency of adverse events associated with CPP.

MATERIAL AND METHODS

In our center, the choice between CPP and FFP is performed before the 1st TPE session at the physicians' discretion. Here, we retrospectively evaluated the efficacy and safety of CPP based on the number of sessions, volume of plasma exposure, frequency of exacerbations/relapses, and adverse events.

RESULTS

Fourteen patients with newly diagnosed TTP were included in this analysis. The proportion of CPP:FFP use was 5:9. There were no significant differences in age, gender, initial hemoglobin, platelet count, LDH, or etiology of TTP between groups. We observed a trend toward a higher number of TPE sessions and higher plasma exposure in CPP, compared to FFP-treated patients. Acute exacerbations were more frequent among patients treated with CPP (OR 26.6; 95%CI 1.01-703.51; P = 0.03). Mild allergic reactions were the most common treatment-related adverse event in both groups.

DISCUSSION

Our data suggest that CPP should not be used as 1st line treatment for newly diagnosed TTP patients.

Postoperative thrombotic thrombocytopenic purpura

Thrombotic thrombocytopenic purpura (TTP) is a rare, life-threatening disease characterized by acute episodes of thrombocytopenia and microangiopathic hemolytic anemia occurring due to platelet and von Willebrand factor deposition and hyaline thrombi formation in arterioles and capillaries throughout the body, which results in organ ischemia. TTP can be idiopathic or secondary, and there are several causes of secondary TTP. There is a clinical syndrome resembling TTP that occurs after surgical procedures, so-called "postoperative TTP" (pTTP). In this review, the differential diagnosis, pathogenesis and clinical and laboratory features of pTTP, together with the treatment modalities and outcomes of the patients, are discussed. The pTTP is a diagnosis of exclusion, and disseminated intravascular coagulation, heparin-induced thrombocytopenia and medication-induced effects should be ruled out. As in classical TTP, patients with pTTP should be diagnosed and treated with therapeutic plasma exchange (TPE) as early as possible to reduce their morbidity and mortality. Although rarely seen, surgeons and physicians of all specialties should be alert to the possibility of pTTP, and since pTTP is a life-threatening event that usually can be treated successfully with TPE, especially when diagnosed early in its course, it is critical to recognize and treat pTTP promptly.

Thrombotic thrombocytopenic purpura: basic pathophysiology and therapeutic strategies

VWF is a multimeric plasma glycoprotein that specifically recruits platelets to sites of vessel injury. VWF multimeric size is central to this function, with larger multimers being more hemostatically active. Regulation of VWF multimeric size is mediated by the plasma metalloprotease ADAMTS13 (A Disintegrin And Metalloproteinase with ThromboSpondin type 1 motifs, member 13). This enzyme can only recognize and cleave VWF when it is unraveled by rheological shear forces of the flowing blood. After the exposure of cryptic exosites, VWF recognition by ADAMTS13 involves multiple interactions that enable the protease to cleave VWF. Loss of VWF multimer size regulation caused by severe ADAMTS13 deficiency (either inherited or acquired) is associated with the microvascular thrombotic disorder thrombotic thrombocytopenic purpura (TTP). The sequelae associated with TTP are widely thought to be linked to hyperreactive circulating VWF that cause unwanted platelet aggregation in the high shear environment of the microvasculature. Diagnosis of TTP is primarily made through a combination of symptoms, analysis of plasma ADAMTS13 activity, and detection of inhibitory anti-ADAMTS13 antibodies. Current frontline treatments for TTP include plasma exchange, which serves to remove inhibitory antibodies (in acquired TTP) and provide a source of functional ADAMTS13, and steroids to treat the autoimmune component of acquired TTP. The use of anti-CD20 therapy has also exhibited encouraging results in the treatment of acquired TTP. Newer therapeutic strategies that are currently being explored or are in development include recombinant ADAMTS13, a hyperreactive ADAMTS13 variant, and anti-VWF therapy. This review discusses the basic biochemistry of VWF and ADAMTS13, their dysfunction in TTP, and therapeutic approaches for the amelioration of TTP.

Historical perspective and future directions in platelet research

Platelets are a remarkable mammalian adaptation that are required for human survival by virtue of their ability to prevent and arrest bleeding. Ironically, however, in the past century, the platelets' hemostatic activity became maladaptive for the increasingly large percentage of individuals who develop age-dependent progressive atherosclerosis. As a result, platelets also make a major contribution to ischemic thrombotic vascular disease, the leading cause of death worldwide. In this brief review, I provide historical descriptions of a highly selected group of topics to provide a framework for understanding our current knowledge and the trends that are likely to continue into the future of platelet research. For convenience, I separate the eras of platelet research into the "Descriptive Period" extending from ~1880-1960 and the "Mechanistic Period" encompassing the past ~50 years since 1960. We currently are reaching yet another inflection point, as there is a major shift from a focus on traditional biochemistry and cell and molecular biology to an era of single molecule biophysics, single cell biology, single cell molecular biology, structural biology, computational simulations, and the high-throughput, data-dense techniques collectively named with the "omics postfix". Given the progress made in understanding, diagnosing, and treating many rare and common platelet disorders during the past 50 years, I think it appropriate to consider it a Golden Age of Platelet Research and to recognize all of the investigators who have made important contributions to this remarkable achievement..

Treatment of bleeding in dialysis patients

Bleeding is a common and potentially serious complication of acute and chronic renal failure. The pathogenesis of bleeding in uremia is multifactorial; however, the major role is played by abnormalities in platelet-platelet and platelet-vessel wall interaction. Platelet dysfunction is partially due to uremic toxins present in circulating blood. Despite decreased platelet function, abnormalities of blood coagulation and fibrinolysis predispose the uremic patients to a hypercoagulable state carrying the risk of cardiovascular and thrombotic complications. Dialysis improves platelet abnormalities and reduces, but does not eliminate, the risk of hemorrhage. Hemodialysis can even contribute to the bleeding through the continuous platelet activation induced by the interaction between blood and artificial surfaces and the use of anticoagulants. Correction of anemia improves hemostasis in uremic patients. Therapeutic management of bleeding in patients with uremia is discussed.

Adenoviral-mediated gene transfer restores plasma ADAMTS13 antigen and activity in ADAMTS13 knockout mice

ADAMTS13 is a plasma metalloprotease that regulates the size of the von Willebrand factor (VWF) multimers. Genetic or acquired deficiency of ADAMTS13 causes thrombotic thrombocytopenic purpura (TTP) in humans. Plasma infusion is the treatment of choice for patients with congenital ADAMTS13 deficiency. However, this practice exposes patients to the risk of infections, allergies and fluid volume overload. The search for alternative treatments is required. Here, we tested the ability of systemically administered adenovirus encoding human ADAMTS13 to restore the deficient protein in the circulation of Adamts13(-/-) mice. Injection of the adenovirus efficiently transduced the liver, kidney, lung, heart and spleen, resulting in the secretion of ADAMTS13 into plasma. A reduced area of thrombi was observed when blood from Ad-ADAMTS13-treated mice was perfused over a collagen-coated surface in a parallel plate flow chamber compared with blood of Ad-betaGal-treated controls. The secreted ADAMTS13 protein was functionally active even after 2 months from injection. The data provide the proof of principle for developing a novel therapy for the correction of ADAMTS13 deficiency in patients with hereditary TTP.

The diagnostic dilemma of thrombotic thrombocytopenic purpura/hemolytic uremic syndrome in the obstetric triage and emergency department: lessons from 4 tertiary hospitals

OBJECTIVE

We report a series of occurrences of thrombotic thrombocytopenic purpura (TTP)/hemolytic uremic syndrome (HUS) in pregnancy that emphasizes early diagnosis.

STUDY DESIGN

Fourteen pregnancies with TTP (n = 12) or HUS (n = 2) were studied. Analysis focused on clinical and laboratory findings on examination, initial diagnosis, and treatment.

RESULTS

There were 14 pregnancies in 12 patients; 2 cases of TTP were diagnosed as recurrent. Five women were admitted to the emergency department (ED), and 7 patients were admitted to an obstetrics triage. Patients who were evaluated by an obstetrician were treated initially for hemolysis, elevated liver enzymes and low platelets syndrome/preeclampsia, whereas patients who were seen in the ED had a diagnosis that is commonplace in the ED (panic attack, domestic violence, gastroenteritis). Latency from the onset of symptoms to diagnosis ranged from 1-7 days. Plasmapheresis treatments in early gestation resulted in favorable maternal-neonatal outcome. Maternal and perinatal mortality rates were 25% each.

CONCLUSION

TTP/HUS is a challenging diagnosis in obstetric triage and ED areas. We propose a management scheme that suggests how to triage patients for early diagnosis in pregnancy.

Molecular basis of ADAMTS13 dysfunction in thrombotic thrombocytopenic purpura

Thrombotic thrombocytopenic purpura (TTP) is a thrombotic microangiopathic disorder characterized by thrombocytopenia, hemolytic anemia, neurological and renal manifestations, and fever. It is associated with dysfunctional von Willebrand factor (VWF) proteolysis and the occurrence of VWF- and platelet-rich thrombi in the microcirculation of multiple organs, including the kidneys. Von Willebrand factor is a large glycoprotein that circulates in plasma as a series of multimers, and it plays a major role in primary hemostasis by inducing the formation of platelet plugs at sites of vascular injury and high-shear stress. Its activity is dependent on the sizes of the multimers, with ultra-large (UL) VWF multimers being biologically very potent. The ULVWF multimers are rapidly degraded upon their secretion from endothelial cells in normal individuals but not in the circulation of TTP patients, causing the formation of disseminated thrombi in the latter. The defective breakdown of VWF is attributed to a severely deficient activity of the VWF-cleaving protease ADAMTS13, a plasma metalloprotease synthesized in the liver, kidneys, and endothelium. This protease rapidly degrades VWF-platelet strings under flow by proteolytic cleavage of the VWF subunit, thereby regulating the size of the platelet thrombus. Congenital TTP occurs due to ADAMTS13 mutations, with the usual debut occurring during the first years of life, while acquired TTP is associated with auto-antibodies against ADAMTS13.

Thrombotic thrombocytopenic purpura in systemic lupus erythematosus: risk factors and clinical outcome: a single centre study

The study was undertaken to investigate clinical characteristics of thrombotic thrombocytopenic purpura (TTP) in patients with SLE and to determine risk factors and clinical outcome of TTP in patients with SLE. Among the 1203 patients with SLE admitted to catholic medical centre of the catholic university of Korea from January 1990 to December 2006, 26 patients with SLE were found to admit with TTP. TTP was defined if microangiopathic haemolytic anaemia, thrombocytopenia and negative Coombs’ test were present and when at least one of the following signs was noted: renal impairment, neurologic deficit or fever. Eighty-seven patients with SLE who admitted with other manifestations, matched for age and sex, were included as disease controls. Data were retrospectively analysed based on medical records. There were no significant demographic characteristics between SLE patients with TTP and those with other manifestations. Multivariate analysis showed that independent risk factors for the development of TTP included high SLE disease activity index score (SLEDAI > 10, P = 0.006) and coexisting nephritis ( P = 0.004). Among the 26 SLE patients with TTP, 12 died during admission period (in-hospital mortality rate: 46.1%). SLE patients with infection or neurologic manifestations had higher mortality rates. Multivariate analysis showed that infection is the only independent risk factor for mortality in SLE patients with TTP ( P = 0.035). Patients with SLE who are in the active stage or who have renal involvement have the increased risk for TTP. Development of TTP in patients with SLE can be fatal. Therefore, intensive therapy will be needed especially in the presence of infection.

Microscopic peliosis of pancreatic islets associated with thrombotic thrombocytopenic purpura

Peliosis is a rarely seen histological finding with unexplained fully etiology and pathogenesis. It is presented as cyst-like blood filled cavities. The presence of peliosis in the endocrine part of the pancreas is extremely rarely reported microscopic phenomenon. The authors provide histological, histochemical, immunohistochemical and ultrastructural investigation of microscopic peliosis in the pancreas from an autopsy case with thrombotic trombocytopenic purpura. The findings give ideas for a wide range of pathophysiological and morphogenetic comments of such an unusual morphologic presentation.

Synergistic interactions between interferon-gamma and TRAIL modulate c-FLIP in endothelial cells, mediating their lineage-specific sensitivity to thrombotic thrombocytopenic purpura plasma-associated apoptosis

Microvascular endothelial cell (MVEC) injury coupled to progression of platelet microthrombi facilitated by ADAMTS13 deficiency is characteristic of idiopathic and HIV-linked thrombotic thrombocytopenic purpura (TTP). Cytokines capable of inducing MVEC apoptosis in vitro are up-regulated in both TTP and HIV infection. However, the concentrations of these cytokines required to elicit EC apoptosis in vitro are 2- to 3-log-fold greater than present in patient plasmas. We report that clinically relevant levels of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and interferon (IFN)-gamma act in synergy to induce apoptosis in dermal MVECs, but have no effect on large-vessel ECs or pulmonary MVECs. This reflects the tissue distribution of TTP lesions in vivo. Sensitivity to TTP plasma or TRAIL plus IFN-gamma is paralleled by enhanced ubiquitination of the caspase-8 regulator cellular FLICE-like inhibitory protein (c-FLIP), targeting it for proteasome degradation. c-FLIP silencing with anti-FLIP short interfering RNA (siRNA) in pulmonary MVECs rendered them susceptible to TTP plasma- and cytokine-mediated apoptosis, while up-regulation of c-FLIP by gene transfer partially protected dermal MVECs from such injury. TTP plasma-mediated apoptosis appears to involve cytokine-induced acceleration of c-FLIP degradation, sensitizing cells to TRAIL-mediated caspase-8 activation and cell death. Suppression of TRAIL or modulation of immunoproteasome activity may have therapeutic relevance in TTP.

Atypical reversible posterior leukoencephalopathy syndrome in thrombotic thrombocytopenic purpura

A 32-year-old man with an atypical form of reversible leukoencephalopathy syndrome (RPLS) caused by thrombotic thrombocytopenic purpura (TTP) is reported. In this particular case, a timely diagnosis of TTP was established primarily on the clinical findings, which led to the early initiation of plasmapheresis and resulted in excellent clinical recovery. The pathophysiological aspects of the relationship between TTP and RPLS are discussed in light of the clinical and radiological features (including diffusion- and perfusion-weighted magnetic resonance imaging studies) of this case. The mechanism for TTP-associated, or TTP-induced, leukoencephalopathy is suggested to be independent of hypertension and vasoconstriction. TTP-associated endothelial injury can play a major role as the inciting mechanism for the development of RPLS.

Intravenous immunoglobulin as an adjunct to plasma exchange for the treatment of chronic thrombotic thrombocytopenic purpura

Thrombotic thrombocytopenic purpura (TTP) is a life-threatening disease. Therapeutic plasma exchange (TPE) is the most effective therapy; however, despite TPE, about one-third of TTP patients will relapse. A subset of patients with TTP has antibodies to ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) and may become resistant to conventional treatments. We describe a patient with TTP and high-titre anti-ADAMTS13 antibodies who developed a chronic, relapsing course of TTP despite frequent TPE. Once adjuvant treatment with intravenous immunoglobulin (IVIG) was added, remission was achieved. Even during remission, anti-ADAMTS13 antibodies remained elevated. We conclude that IVIG may sustain remission in some patients with chronic, relapsing TTP.

Severe limb necrosis: primary thrombotic microangiopathy or “seronegative” catastrophic antiphospholipid syndrome? A diagnostic dilemma

An episode of gastroenteritis triggered severe necrosis of all extremities in a previously asymptomatic male. Hepatic and renal involvement were also manifest, while the hematological picture was one of thrombotic microangiopathic hemolytic anemia. Antiphospholipid antibodies were negative. He responded well to a combination of plasma exchange, anticoagulation (heparin), parenteral steroids, and antibiotics, as well as vasodilators (prostacycline) and hyperbaric oxygen, but died because of a cerebral hemorrhage. The differential diagnosis included thrombotic thrombocytopenic purpura/hemolytic-uremic syndrome, or seronegative catastrophic antiphospholipid (Asherson's) syndrome. The dangers of administering such a combination of therapies with anticoagulation, as well as vasodilatation (prostacycline) and hyperbaric oxygen, are highlighted by the case report and emphasized.