Relapsed thrombotic thrombocytopenic purpura presenting as an acute cerebrovascular accident

Thrombotic Thrombocytopenic Purpura Without Evidence of Microangiopathic Hemolytic Anemia: A Case Report

Diagnosis of thrombotic thrombocytopenic purpura (TTP) is challenging due to varied clinical presentations and is primarily based on ADAMTS13 activity assay, however clinical suspicion to include TTP as a potential diagnosis relies on multiple scoring systems all involving hemolysis as a prime feature. Here, we report a case of TTP without any evidence of microangiopathic hemolytic anemia (MAHA). A 65-year-old male admitted with a Glasglow come scale of 3 was intubated and sedated on admission. Complete blood count was concerning for a hemoglobin (Hb) of 5.8 g/dL, and a platelet count of 76 k/µL. The patient had a bleeding episode while placing a central line; the repeat platelet count was found to be 35 k/µL, further dropping to 14 k/µL the next day. Coagulation studies now reflected PT of 19.8 sec, aPTT of 38.7 sec, and fibrinogen of 212 mg/dL. The peripheral smear showed no evidence of hemolysis. TTP was kept low on the differential and haematological anomalies were attributed to possible disseminated intravascular coagulation (DIC) from sepsis and liver disease. ADAMSTS13 was incidentally checked upon admission, later resulting in <5% activity with a Bethesda titer inhibitor of 3.2. The patient was immediately initiated on plasmapheresis along with prednisone. Additionally, rituximab and caplacizumab were added. Plasmapheresis was continued for ten sessions until the platelet count reached 167 k/µL. At the time of discharge, laboratory values revealed platelets of 251 k/µL and hemoglobin of 8.8 g/dL. We recognize that the diagnosis of TTP is challenging because of its diverse clinical manifestations and constrained availability of ADAMTS13 testing. Clinical prediction scores have been developed to estimate the pretest probability of severe ADAMTS13 deficiency, however, they all include the presence of MAHA. Atypical presentation of TTP has been previously acknowledged however continues to remain under-recognized.

Two ischemic stroke events within 48 h: a case report of an unusual presentation of thrombotic thrombocytopenic purpura

BACKGROUND

Thrombotic thrombocytopenic purpura (TTP) considers a rare cause of ischemic stroke (IS). We reported a case of a newly diagnosed patient with acquired immune-mediated TTP (iTTP), in whom two IS events developed during 48 h.

CASE PRESENTATION

A 59-year-old diabetic male was presented to the hospital 24 h after symptoms onset, including left hemiparesis, dysarthria, and decreased consciousness. A brain CT scan was performed with the suspicion of acute IS, indicating infarct lesions in the right middle cerebral artery (MCA) territory. The patient was not eligible for thrombolytic therapy due to admission delay. Over the next 24 h, the patient's neurological condition deteriorated, and the second brain CT scan showed new ischemic lesions in the left MCA territory. Initial laboratory evaluation indicated thrombocytopenia without evidence of anemia. However, in the following days, thrombocytopenia progressed, and microangiopathic hemolytic anemia (MAHA) developed. The ADAMTS-13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) activity and inhibitors assay confirmed the diagnosis of iTTP. The patient underwent plasma exchange activity and inhibitors assay confirmed the diagnosis of iTTP. The patient underwent and pulse IV methylprednisolone. Rituximab was also added due to the refractory course of the disease. After a prolonged hospital course, he had considerable neurologic recovery and was discharged.

CONCLUSIONS

Clinicians should consider two points. First, TTP should be considered in any patient presenting with IS and having thrombocytopenia or anemia without other symptoms of TTP. Second, worsening the patient's condition during hospitalization may indicate a new stroke and should be investigated immediately.

THROMBOTIC MICROANGIOPATHY: DIAGNOSTIC CHALLENGES IN THE PRIMARY MULTIPLE NEOPLASM INVOLVEMENT WITH PREVALENT METASTASIS WITH GRANULOMATOSIS INFLAMMATORY FOCUSES

Patient, who died during the hospital stay, had hemoblastosis and syphilis in the reported medical history. While the patient was examined doctors suspected the presence of malignancy with unknown primary localization with multiple metastatic injuries with clinical and laboratory TTP signs (hemorrhagic syndrome, thrombocytopenia, shystocytosis, and non-immune hemolytic anemia). Despite treatment, the general patient's condition progressively worsens with increasing multiple organ decompensation signs. In the final stage of the disease course, after heart arrest and the appearance of clinical death signs CPR measures were performed according to complete guidance, but CRP had no positive effect. Biological death was constated. Considering the criteria of the diagnostic clinical and laboratory dyad (thrombocytopenia and microangiopathic hemolytic anemia), the data of the patholog¬ical examination (multiple metastatic lesions, inflammatory process, tumor intoxication, thrombosis), the combination of manifestations of chronic myeloid leukemia, prostate cancer with multiple metastases, tertiary syphilis served as a condition for the initiation of TTP, which was of decisive importance in the development of the patient's death.

Endocarditis-induced thrombotic thrombocytopenic purpura mimicking preeclampsia: A case report

TTP, Preeclampsia have similar manifestations in pregnancy. Establishing the right diagnosis is essential as the treatment is different. Endocarditis-induced TTP should be suspected when neurological symptoms, thrombocytopenia are present.

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.

Cerebral Infarction in Immune Thrombotic Thrombocytopenic Purpura Is Associated with Old Age, Hypertension, Smoking, and Anti-ADAMTS13 Ig, But Not with Mortality

Background  Neurological involvement is common in patients with immune thrombotic thrombocytopenic purpura (iTTP), but the frequency, risk factors, and outcomes of these with imaging-confirmed stroke in iTTP are not known. Methods  We selected 66 out of 109 iTTP patients with neurological signs and symptoms and reviewed their CT/MRI (computed tomography/magnetic resonance imaging) findings for the evidence of stroke and other clinical information in Alabama TTP Registry. Results  Of these, 52 (78.8%) had their CT/MRI done on admission in whom 22 (42.3%) were positive for multiple acute or chronic infarcts. The patients with image-confirmed ischemic stroke were older, and appeared to be associated with a history of hypertension and smoking. Additionally, patients with imaging-confirmed stroke showed higher plasma concentrations of anti-ADAMTS13 IgG than those without stroke. More interestingly, there was no statistically significant difference in the rate of exacerbation and 60-day mortality between those with and without stroke. Conclusion  Ischemic cerebral infarcts are common findings in brain imaging studies of patients with acute iTTP; old age, chronic hypertension, and smoking, as well as high plasma concentrations of anti-ADAMTS13 IgG may be the potential risk factors for cerebral infarction in these patients. The presence of image-confirmed ischemic stroke, however, does not predict exacerbation and 60-day mortality, although the long-term effect of such ischemic brain damage on cognitive function and quality of life remains to be determined.

Good practice statements (GPS) for the clinical care of patients with thrombotic thrombocytopenic purpura

BACKGROUND

Despite advances in treatment options for thrombotic thrombocytopenic purpura (TTP), there are still limited high quality data to inform clinicians regarding its management.

METHODS

In June 2018, the ISTH formed a multidisciplinary guideline panel to issue recommendations about treatment of TTP. The panel discussed 12 treatment questions related to both immune-mediated TTP (iTTP) and hereditary/congenital TTP (cTTP). The panel used the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach, including evidence-to-decision frameworks, to appraise evidence and formulate recommendations.

RESULTS

The panel agreed on eleven recommendations based on evidence ranging from very low to moderate certainty. For first episode and relapses of acute iTTP, the panel made a strong recommendation for the addition of corticosteroids to therapeutic plasma exchange (TPE), and a conditional recommendation for addition of rituximab and caplacizumab. For asymptomatic iTTP with low ADAMTS13, the panel made a conditional recommendation for rituximab outside of pregnancy, and for prophylactic TPE during pregnancy. For asymptomatic cTTP, the panel made a strong recommendation for prophylactic plasma infusion during pregnancy, but a conditional recommendation for plasma infusion or a wait and watch approach outside of pregnancy.

CONCLUSIONS

The panel's recommendations are based on all the available evidence for the treatment effects of various approaches including suppressing inflammation, blocking platelet clumping, replacing the missing and/or inhibited ADAMTS13, and suppressing ADAMTS13 antibody production. There was insufficient evidence for further comparison of different treatment approaches, for which future high-quality studies in iTTP (e.g., rituximab, corticosteroids, recombinant ADAMTS13, and caplacizumab) and in cTTP (eg, recombinant ADAMTS13) are needed.

Atypical Thrombotic Thrombocytopenic Purpura Presenting as Stroke

Here we report a case of atypical thrombotic thrombocytopenic purpura that presented as an ischemic cerebrovascular accident. A 56-year-old man with multiple cardiovascular risk factors presented with sudden left-sided weakness, slurred speech, and left facial droop. He showed mild improvement when he was treated with thrombolytic therapy according to the hospital stroke protocol. Later in the course, he developed thrombocytopenia followed by schistocytes revealed by peripheral blood smear and other lab abnormalities. Thrombotic thrombocytopenic purpura (TTP) was suspected, and he was treated with total plasma exchange that improved his condition significantly. This case shows that TTP can have unusual and atypical presentations either with the first episode or upon relapse, making diagnosis extremely difficult. Because patients may not present the expected clinical findings, it is important to be aware of variant presentations. In the early stages of the disease, platelet aggregation and thrombus formation may not be widespread, and thrombocytopenia and microangiopathic hemolytic anemia may not be clinically evident. Patients can present soon after the onset of symptoms when the typical laboratory abnormalities may not have had ample time to manifest. Although most other similar cases in the literature had a previous typical presentation of the disease before an atypical presentation, our patient's first presentation was atypical. An atypical presentation of disease in a patient with cardiovascular risk factors may therefore be extremely difficult to diagnose. We believe that TTP should be considered for any patient presenting with stroke and thrombocytopenia.

Immune-Thrombotic Thrombocytopenic Purpura is a Rare Cause of Ischemic Stroke in Young Adults: Case Reports and Literature Review

INTRODUCTION

Immune thrombotic thrombocytopenic purpura (i-TTP), related to acquired ADAMTS-13 dysfunction, can lead to various neurological symptoms including ischemic stroke. To date the clinical, radiological, and biological characteristics of patients having a stroke as the inaugural manifestation of i-TTP are largely unknown.

METHODS

Probable immune-TTP was defined by a low ADAMTS-13 activity associated with the presence of ADAMTS-13 inhibitors and/or favorable clinicobiological response under immunological treatments. The clinical, radiological, biological data and outcome under treatment are described in a cohort of 17 patients coming from 3 local cases and a literature review.

RESULTS

Fourteen of the 17 patients were female and the mean age was 41 years. None of the patients had the classical pentad of TTP. Only 41% had a combination of thrombocythemia and hemolysis. Stroke was multifocal in 35% and included large artery strokes. No adverse event was observed following intravenous thrombolysis. Refractory and relapsing forms were observed in 47%.

DISCUSSION

The clinical, radiological, and biological presentation of patients with stroke as the inaugural presentation of i-TTP is heterogeneous. This diagnosis should be discussed in every young adult with ischemic stroke of undetermined source.

A rare combination of thrombotic thrombocytopenic purpura and antiphospholipid syndrome

: Thrombocytopenia, in the setting of microangiopathic hemolytic anemia and thrombotic events, is characteristic of both thrombotic thrombocytopenic purpura and primary antiphospholipid syndrome. Clinically, it is difficult to distinguish between these two syndromes. We present a 41-year-old woman with chronic, relapsing thrombotic thrombocytopenic purpura in the presence of antiphospholipid antibodies. She had clinical manifestations of antiphospholipid syndrome without meeting laboratory criteria of the Sydney classification system. In the literature, there have only been nine cases of thrombotic thrombocytopenic purpura associated with primary antiphospholipid syndrome. Seven of the nine cases suffered from one or multiple strokes, a common feature in antiphospholipid syndrome, but an uncommon finding in thrombotic thrombocytopenic purpura. We introduce the possibility of an association between thrombotic thrombocytopenic purpura and the presence of antiphospholipid antibodies. Systematic testing of ADAMTS13 activity and anti-ADAMTS13 antibodies in patients who present with neurological symptoms and thrombocytopenia, in the presence of antiphospholipid antibodies, may help with the diagnosis of the rare thrombotic thrombocytopenic purpura-antiphospholipid syndrome combination.

Atypical presentations of thrombotic thrombocytopenic purpura: a diagnostic role for ADAMTS13

Thrombotic thrombocytopenic purpura (TTP) is an acute, life threatening disease. Only a minority of patients expresses the complete clinical presentation and unusual manifestations can occur. Demonstration of low activity levels of ADAMTS13 (<5 %) is highly specific for the diagnosis of TTP. This study reports a series of five cases of TTP presenting with a thrombotic event and no hematological findings. Detailed chart reviews on these patients were conducted. We identified two patients whose first attack of TTP presented as a thrombotic episode without microangiopathic hemolytic anemia and thrombocytopenia, only to be diagnosed as TTP days later, after the appearance of hematological signs. We also describe three cases of classical TTP relapsing atypically as cerebrovascular accidents without hematological signs. Low levels of ADAMTS13 activity were detected and facilitated the diagnosis. The neurological manifestations disappeared concurrent with normalization of ADAMTS13 activity level after plasma exchange. This study underscores the importance of having a high clinical suspicion of TTP in cases of thrombosis even without hematological abnormalities in patients with previous attacks of TTP. In this clinical scenario, measurement of ADAMTS13 activity is important for diagnosis and early administration of treatment.

Prognostic risk-stratified score for predicting mortality in hospitalized patients with thrombotic thrombocytopenic purpura: nationally representative data from 2007 to 2012

BACKGROUND

Despite proven efficacy and increased availability of therapeutic plasma exchange (TPE), mortality for patients with thrombotic thrombocytopenic purpura (TTP) remains high with a limited understanding of those at highest risk of death.

STUDY DESIGN AND METHODS

This study utilized the Nationwide Inpatient Sample (2007-2012) to derive a prognostic score for mortality in hospitalized TTP patients. Odds ratios of death with various putative risk factors adjusted for age, sex, and race were calculated (adjOR). Weighted mean of adjOR estimates were incorporated in a risk-stratified score.

RESULTS

Among 8203 hospitalizations with TTP as primary admission diagnosis who underwent TPE, 613 deaths were identified (all-cause mortality, 7.5%; median time-to-death, 9 days; interquartile range, 4-14 days). In multivariable logistic regression, arterial thrombosis (adjOR 6.7, 95% confidence interval [CI], 1.1-40.9), intracranial hemorrhage (adjOR, 6.1; 95% CI, 1.6-23.2), age at least 60 years (adjOR, 3.5; 95% CI, 2.1-5.6), renal failure (adjOR, 2.6; 95% CI, 1.5-4.5), ischemic stroke (adjOR, 2.4; 95% CI, 1.2-5.0), platelet (PLT) transfusions (adjOR, 2.2; 95% CI, 1.2-4.1), and myocardial infarction (adjOR, 2.3; 95% CI, 1.2-4.6) were significant independent predictors of mortality in TTP patients who underwent TPE. A prognostic weighted mortality prediction scoring system incorporating arterial thrombosis, intracranial hemorrhage, age, renal failure, ischemic stroke, PLT transfusion, and myocardial infarction showed very good discrimination and was predictive of 78.6% deaths.

CONCLUSIONS

Early and targeted therapy for high-risk individuals should be used to guide management of TTP patients for improved survival outcomes.

Resolution of internal carotid dissection with middle cerebral artery occlusion in pregnancy

Introduction. Cervical artery dissection (CAD) is a common cause of stroke in younger patients. While the incidence of stroke in pregnancy is increasing, CAD remains a rare cause of ischemic stroke in the pregnant population, with only 30 cases described in the literature, most in the postpartum period. Methods. The case of a pregnant patient at 18 weeks of gestation presenting with CAD and ischemic stroke following intercourse is discussed. Discussion. CAD results from an intimal tear in the carotid artery, allowing accumulation of blood in the vessel wall. Stroke results from embolization of thrombogenic material in the wall. Etiology includes minor trauma, connective tissue disorders, or anatomic variations of the carotid artery. Most patients present with headache and/or neck pain, while ischemic symptoms are seen in at least 50% of patients. In the pregnant population, imaging with MRI or MRA of the head and neck aids in diagnosis. Once the diagnosis is made, patients are treated with either anticoagulation or antiplatelet medications. The optimal treatment in both pregnant and nonpregnant patients has not been well-studied. Conclusion. CAD is an important diagnosis to consider in a pregnant patient with persistent headache, especially if neurological symptoms are present. Imaging should be quickly obtained so treatment can be initiated.

Atypical thrombotic thrombocytopenic purpura in a middle-aged woman who presented with a recurrent stroke

An atypical clinical presentation makes TTP diagnosis difficult, which prevents prompt management of TTP. This case highlights the importance of early recognition of TTP in patients with atypical presentations who may not have the expected clinical or laboratory findings. The level of suspicion should be especially high in young and middle-aged patients with strokes or acute coronary syndrome who do not have other risk factors for cardiovascular events. This is particularly so for those patients who have a previous episode of TTP or patients with subtle laboratory abnormalities, which may suggest the potential existence of a thrombotic microangiopathic process.

Stroke due to typical thrombotic thrombocytopenic purpura treated successfully with intravenous thrombolysis and therapeutic plasma exchange

We report a case of a 39-year-old man with expressive aphasia due to occlusion of the temporal stem of the left middle cerebral artery. Laboratory tests showed microangiopathic haemolytic anaemia and thrombocytopenia. A thrombotic thrombocytopenic purpura (TTP) was diagnosed, and thrombolytic therapy (TT) with alteplase followed by therapeutic plasma exchange (TPE) were performed with complete resolution of symptoms. The gold standard TTP treatment is TPE, and its delay can be lethal. The use of TT in TTP is controversial and has potential risks. This case shows a successful TT in a patient with typical TTP presenting as a stroke due to a large cerebral artery occlusion.

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

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

A review of hereditary and acquired coagulation disorders in the aetiology of ischaemic stroke

The diagnostic workup in patients with ischaemic stroke often includes testing for prothrombotic conditions. However, the clinical relevance of coagulation abnormalities in ischaemic stroke is uncertain. Therefore, we reviewed what is presently known about the association between inherited and acquired coagulation disorders and ischaemic stroke, with a special emphasis on the methodological aspects. Good-quality data in this field are scarce, and most studies fall short on epidemiological criteria for causal inference. While inherited coagulation disorders are recognised risk factors for venous thrombosis, there is no substantial evidence for an association with arterial ischaemic stroke. Possible exceptions are the prothrombin G20210A mutation in adults and protein C deficiency in children. There is proof of an association between the antiphospholipid syndrome and ischaemic stroke, but the clinical significance of isolated mildly elevated antiphospholipid antibody titres is unclear. Evidence also suggests significant associations of increased homocysteine and fibrinogen concentrations with ischaemic stroke, but whether these associations are causal is still debated. Data on other acquired coagulation abnormalities are insufficient to allow conclusions regarding causality. For most coagulation disorders, a causal relation with ischaemic stroke has not been definitely established. Hence, at present, there is no valid indication for testing all patients with ischaemic stroke for these conditions. Large prospective population-based studies allowing the evaluation of interactive and subgroup effects are required to appreciate the role of coagulation disorders in the pathophysiology of arterial ischaemic stroke and to guide the management of individual patients.

Stroke in a young patient treated by alteplase heralding an acquired thrombotic thrombocytopenic purpura

BACKGROUND AND PURPOSE

Thrombotic thrombocytopenic purpura (TTP) is a life-threatening multisystem disorder characterized by thrombocytopenia and fluctuating neurological symptoms due to microinfarcts. In rare cases, large cerebral arteries can be occluded.

SUMMARY OF THE CASE

We report on a 30-year-old woman with a first-ever acute stroke related to a right proximal MCA M1 occlusion. Platelet count was normal at admission and progressively decreased 6 days after intravenous thrombolysis with the occurrence of a hemolytic anemia with schistocytes. Most biological anomalies reversed after plasma exchange. No hemorrhagic complication occurred. Diagnosis of initial TTP was confirmed by low ADAMTS13 activity and positivity of anti-ADAMTS13 antibody.

CONCLUSION

This observation highlights the fact that even if platelet count and hemoglobin rate are normal in the beginning, an acute ischemic stroke in a young patient can be related to TTP. Faced with subsequent thrombopenia, practitioners should be aware of acquired TTP, and, thus, schistocytes, haptoglobin, and LDH assays should be performed. Early diagnosis is paramount to start the life-saving plasma exchanges.

Pathophysiology of thrombotic thrombocytopenic purpura

Thrombotic thrombocytopenic purpura (TTP) is a disorder with characteristic von Willebrand factor (VWF)-rich microthrombi affecting the arterioles and capillaries of multiple organs. The disorder frequently leads to early death unless the patients are treated with plasma exchange or infusion. Studies in the last decade have provided ample evidence to support that TTP is caused by deficiency of a plasma metalloprotease, ADAMTS13. When exposed to high shear stress in the microcirculation, VWF and platelets are prone to form aggregates. This propensity of VWF and platelet to form microvascular thrombosis is mitigated by ADAMTS13, which cleaves VWF before it is activated by shear stress to cause platelet aggregation in the circulation. Deficiency of ADAMTS13, due to autoimmune inhibitors in patients with acquired TTP and mutations of the ADAMTS13 gene in hereditary cases, leads to VWF-platelet aggregation and microvascular thrombosis of TTP. In this review, we discuss the current knowledge on the pathogenesis, diagnosis and management of TTP, address the ongoing controversies, and indicate the directions of future investigations.

Atypical presentations of thrombotic thrombocytopenic purpura: a review

Thrombotic thrombocytopenic purpura (TTP) is diagnosed by the presence of microangiopathic hemolytic anemia and thrombocytopenia in a patient who frequently presents with central nervous system involvement and, to a lesser extent, renal dysfunction. Recent understanding of the pathophysiology of TTP due to severe deficiency of von Willebrand factor cleaving protease, known as ADAMTS13, has improved diagnosis of TTP. Once the diagnosis is suspected, life-saving therapeutic plasma exchange therapy is initiated. Occasionally, an unusual clinical presentation makes TTP diagnosis difficult, thus resulting in a delay in the management of TTP. This review highlights a variety of atypical TTP presentations described in the literature. It is intended to bring unusual scenarios to the clinician's awareness, so that timely treatment can be delivered.

Von Willebrand factor, ADAMTS13, and thrombotic thrombocytopenic purpura

Discoveries during the past decade have revolutionized our understanding of idiopathic thrombotic thrombocytopenic purpura (TTP). Most cases in adults are caused by acquired autoantibodies that inhibit ADAMTS13, a metalloprotease that cleaves von Willebrand factor within nascent platelet-rich thrombi to prevent hemolysis, thrombocytopenia, and tissue infarction. Although approximately 80% of patients respond to plasma exchange, which removes autoantibody and replenishes ADAMTS13, one third to one half of survivors develop refractory or relapsing disease. Intensive immunosuppressive therapy with rituximab appears to be effective as salvage therapy, and ongoing clinical trials should determine whether adjuvant rituximab with plasma exchange also is beneficial at first diagnosis. A major unanswered question is whether plasma exchange is effective for the subset of patients with idiopathic TTP who do not have severe ADAMTS13 deficiency.

Thrombotic thrombocytopenic purpura: a thrombotic disorder caused by ADAMTS13 deficiency

A serious disorder with characteristic microvascular thrombosis involving the brain and other organs, thrombotic thrombocytopenic purpura (TTP) typically presents with thrombocytopenia, hemolysis with schistocytes on blood smears, and mental changes or seizures. It may progress rapidly to a fatal end if the patient is not treated immediately with plasma. Recent advances have shown that TTP is caused by deficiency of a circulating, von Willebrand factor cleaving metalloprotease, ADAMTS13. This new knowledge will provide clues to improve the diagnosis and management of this intriguing disease.

Journey in reverse: TTP from bedside to blood bank to bench

Thrombotic thrombocytopenic purpura (TTP) is the most extensive and dangerous intravascular platelet clumping disorder. For more than a half-century after its initial recognition, mortality was near 100% and the etiology totally obscure. Then, in the late 1970s to early 1980s, empiric, but successful, therapy by a few clinician/blood bank partnerships was followed by sudden laboratory insight into pathophysiology. The discussion that follows was prepared in conjunction with the 2006 Francis Morrison, M.D., Memorial Lecture at the 27th Annual Meeting of the American Society for Apheresis.

ADAMTS13 and microvascular thrombosis

Interaction between platelet and von Willebrand factor, a circulating adhesive glycoprotein, is essential for hemostasis under the high shear environments of arterioles and capillaries. If unregulated, this interaction may lead to unwarranted platelet thrombosis. ADAMTS13 (a disintegrin and metalloprotease with thrombospondin type 1 motif, number 13), a plasma zinc metalloprotease synthesized primarily in the stellate cells of the liver, cleaves shear stress-activated von Willebrand factor, thereby preventing the occurrence of von Willebrand factor-platelet interaction in the circulation. A profound deficiency of ADAMTS13, due to genetic mutations or autoimmune inhibition, results in intravascular von Willebrand factor platelet aggregation and widespread microvascular thrombosis characteristic of thrombotic thrombocytopenic purpura. Cloning of ADAMTS13 and structure-function analyses of the enzyme are leading to exciting advances in the diagnosis and therapy of this hitherto mysterious disease.

Current concepts in thrombotic thrombocytopenic purpura

Recent advances have demonstrated that thrombotic thrombocytopenic purpura (TTP), characterized by widespread thrombosis in the arterioles and capillaries, is caused by deficiency of a circulating zinc metalloprotease, ADAMTS13. Two types of TTP are recognized: autoimmune TTP, caused by inhibitory antibodies of ADAMTS13, and hereditary TTP, caused by genetic mutations of ADAMTS13. This article reviews the characteristics and function of ADAMTS13, the mechanism by which ADAMTS13 deficiency may lead to thrombosis, and the causes of ADAMTS13 deficiency. It also discusses how the new knowledge may improve the diagnosis and treatment of this previously mysterious disorder.

Thrombotic thrombocytopenic purpura: a moving target

Almost 80 years after Eli Moschcowitz published the first description of the disease, most patients with idiopathic thrombotic thrombocytopenic purpura (TTP) were found to have acquired autoantibody inhibitors of the ADAMTS13 metalloprotease. Plasma ADAMTS13 normally cleaves von Willebrand factor within nascent platelet-rich thrombi, and ADAMTS13 deficiency allows unchecked thrombus growth to cause microangiopathic hemolysis, thrombocytopenia, and tissue infarction. At present, ADAMTS13 deficiency with a high-titer inhibitor level appears to be associated with an increased risk of early death and subsequent relapse. Thus, acquired ADAMTS13 deficiency identifies a specific mechanism of TTP and is a potential biomarker of disease activity or risk. At present, two major clinical questions in the field may be summarized as follows. First, by emphasizing TTP caused by ADAMTS13 deficiency, are we in danger of neglecting other causes that should be treated with plasma exchange? Second, should we treat asymptomatic patients who have severe ADAMTS13 deficiency to prevent future disease, and if so, how?

Recent advances in thrombotic thrombocytopenic purpura

Thrombotic thrombocytopenic purpura (TTP) is characterized by microangiopathic hemolytic anemia and thrombocytopenia, accompanied by microvascular thrombosis that causes variable degrees of tissue ischemia and infarction. Intravascular coagulation is not a prominent feature of the disorder. Plasma exchange can induce remissions in approximately 80% of patients with idiopathic TTP, but patients have a much worse prognosis when thrombotic microangiopathy is associated with cancer, certain drugs, infections, or tissue transplantation. Recently, acquired autoimmune deficiency of a plasma metalloprotease named ADAMTS13 was shown to cause many cases of idiopathic TTP. This review describes our current understanding of how to use this knowledge clinically. In Section I, Dr. Joel Moake describes the presentation of thrombotic microangiopathy, emphasizing the pathophysiology of idiopathic TTP. Platelets adhere to ultra-large (or "unusually large") von Willebrand factor (ULVWF) multimers that are immobilized in exposed subendothelial connective tissue and secreted into the circulation in long "strings" from stimulated endothelial cells. ADAMTS13 cleaves ULVWF multimers within growing platelet aggregates under flowing conditions, and this normally limits platelet thrombus formation. If ADAMTS13 is absent, either congenitally or due to acquired autoantibodies, platelet-rich microvascular thrombosis proceeds unchecked and TTP ensues. Plasma exchange is effective therapy for idiopathic TTP, probably because it replenishes the deficient ADAMTS13 and removes some of the pathogenic autoantibodies and endothelial-stimulating cytokines. Some patients have a type of thrombotic microangiopathy after transplantation/chemotherapy but do not have severe ADAMTS13 deficiency. The pathogenesis of their disease must differ but remains poorly understood. In Section II, Dr. Toshiyuki Miyata describes recent advances in assay methods that should facilitate routine laboratory testing of ADAMTS13 for patients with thrombotic microangiopathy. ADAMTS13 cleaves a single Tyr-Met bond in domain A2 of the VWF subunit. ADAMTS13 assays based on the cleavage of plasma VWF multimers have been used extensively but require considerable time and expertise to perform. A recombinant substrate containing 73 amino acid residues of VWF domain A2 has been devised that allows short incubation times and rapid product detection by gel electrophoresis or immunoassay. These results should encourage the development of even simpler assays that can be performed in most clinical laboratories. In Section III, Dr. James George provides an update on the long-term prospective study of thrombotic microangiopathy in the Oklahoma TTP-HUS Registry. At presentation, the clinical distinction between idiopathic TTP, various forms of secondary thrombotic microangiopathy, and even Shiga toxin-associated hemolytic uremic syndrome (HUS) can be problematic because the symptoms and laboratory findings often overlap. Consequently, plasma exchange usually is administered to any patient with thrombotic microangiopathy if there is doubt about the cause. The role of ADAMTS13 testing in choosing therapy remains uncertain, but the results do appear to have prognostic significance. Severe ADAMTS13 deficiency is specific for idiopathic TTP and identifies a subgroup with a high likelihood of response to plasma exchange, and high-titer ADAMTS13 inhibitors correlate strongly with a high risk of relapsing disease. Patients with normal ADAMTS13 activity have a much worse prognosis, although many factors probably contribute to this difference. Longitudinal study of these patients will continue to clarify the relationship of ADAMTS13 deficiency to the clinical course of thrombotic microangiopathy.