Thrombotic thrombocytopenic purpura: a moving target

Thrombotic microangiopathy in patients with sickle cell disease

OBJECTIVE

To describe two cases of patients who had thrombotic microangiopathy (TMA) associated with sickle cell disease (SCD).

CASE DESCRIPTION

Both patients started with a painful crisis and had acute chest syndrome during hospitalization. They showed significant worsening of hemolytic anemia, with very high levels of lactate dehydrogenase, thrombocytopenia, lowered level of consciousness, organ damage and the presence of schistocytes in peripheral blood. Due to the possibility of TMA, despite the very rare association with SCD, they were treated with fresh frozen plasma replacement and plasmapheresis, with good response.

COMMENTS

TMA is a serious, life-threatening disease, characterized by microangiopathic hemolytic anemia, thrombocytopenia, and organ damage. The association of SCD and TMA is difficult to diagnose, since they can share a similar clinical presentation. Recognizing this association and promptly instituting treatment may impact the survival of these patients.

Von Willebrand Factor in Health and Disease

Abstract—

Von Willebrand factor (vWF), the key component of hemostasis, is synthesized in endothelial cells and megakaryocytes and released into the blood as high molecular weight multimeric glycoproteins weighing up to 20 million Daltons. Blood plasma metalloprotease ADAMTS13 cleaves ultra-large vWF multimers to smaller multimeric and oligomeric molecules. The vWF molecules attach to the sites of damage at the surface of arterioles and capillaries and unfold under conditions of shear stress. On the unfolded vWF molecule, the regions interacting with receptors on the platelet membrane are exposed. After binding to the vWF filaments, platelets are activated; platelets circulating in the vessels are additionally attached to them, leading to thrombus formation, blocking of microvessels, and cessation of bleeding. This review describes the history of the discovery of vWF, presents data on the mechanisms of vWF secretion and its structure, and characterizes the processes of vWF metabolism in the body under normal and pathological conditions.

Allogeneic reactivity-mediated endothelial cell complications after HSCT: a plea for consensual definitions

Endothelial cell (EC) activation has been suspected of triggering a group of rare and dismal complications that can occur after allogeneic hematopoietic stem cell transplantation (HSCT). Capillary leak syndrome, engraftment syndrome, transplant-associated microangiopathy, diffuse alveolar hemorrhage, and idiopathic pneumonia syndrome are the main nosological entities. Post-HSCT endotheliitis can be triggered by chemotherapy, infections, and calcineurin inhibitors, but allogeneic reactivity is claimed to be the common denominator. Endothelial damages are thought to activate several deleterious pathways (proapoptotic, procoagulant, proinflammatory) and can lead to multiorgan failure; however, clinical manifestations of each syndrome overlap, and their relationship with graft-versus-host disease could be minimal. The lack of well-defined diagnostic criteria does not allow for a clear-cut comparison in the current literature. Therapeutic efforts have been made to intercept the pathogenic mechanisms leading to EC dysfunction, but remission rates and survival remain mostly unsatisfactory. In this article, we have reviewed the incidence, clinical features, and treatment approaches of EC activation syndromes, and we plead for the development of internationally accepted standard definitions.

Thrombotic thrombocytopenic purpura in a new onset lupus patient?

We are presenting a case of TTP with undetectable levels of ADAMTS 13 in a 39-year-old woman. Diagnosis of systemic lupus was evoked in the setting of thrombotic microangiopathy. The patient presented normal renal function but important neurological impairment. Treatment with daily plasmapheresis as well as Rituximab, cyclophosphamide as steroids was required to achieve clinical improvement.

Recombinant thrombomodulin for secondary thrombotic thrombocytopenic purpura

In the pathogenesis of thrombotic thrombocytopenic purpura (TTP), reductions in the enzyme activity of ADAMTS13, which cuts ultralarge von Willebrand multimers, generates shear stress on the microvascular endothelium, leading to platelet aggregation and the formation of a thrombus. ADAMTS13 activity is markedly decreased in typical TTP, but is only mildly reduced in secondary TTP, which concomitantly develops with primary disease. The latter develops with septic disseminated intravascular coagulation (DIC) and often causes organ failure. Recombinant thrombomodulin (rTM) is a drug that is used to treat DIC and may also remit TTP because it improves vascular endothelial dysfunction. Therefore, we herein investigated the efficacy of rTM in patients treated for the pathology of secondary TTP. Patients who were admitted to the Emergency and Critical Care Center of our hospital and met the following conditions were extracted and retrospectively analyzed: hemolytic anemia accompanied by fragmented red blood cells (Hb < 12 g/dL or lower); thrombocytopenia (<100 × 10/μL); and ADAMTS13 activity <50%. Sixteen patients were included and accompanied by Kidney Disease: Improving Global Outcomes (KDIGO) stage 2 or more severe nephropathy and DIC. Eleven and 5 patients treated with and without rTM (the rTM and non-rTM treatment groups, respectively) were compared, and no significant difference was noted in their basic characteristics, such as background disease and severity. No significant difference was observed in survival rates; however, the platelet count, which is an important outcome of treatments for TTP, significantly increased in the rTM treatment group: 3.3 ± 2.6→11.3 ± 14.6 versus 3.5 ± 3.7→5.7 ± 3.9 (×1000/μL) (P = 0.034). Thrombotic thrombocytopenic purpura originally requires invasive treatments and its prognosis is not favorable. Blood thrombomodulin levels also markedly increase due to vascular endothelial dysfunction, whereas rTM alleviates vascular endothelial dysfunction in TTP patients with high blood TM levels, suggesting the importance of administering rTM. Thus, rTM may be effective for secondary TTP and may be adopted as adjuvant therapy.

Clinical utility of ADAMTS-13 testing in suspected thrombotic microangiopathy: an audit of ADAMTS-13 activity assay requests in routine practice from a tertiary hospital

AIMS

Differentiation between thrombotic thrombocytopenic purpura (TTP) and other microangiopathic haemolytic anaemia (MAHA) processes can be difficult. Since the documentation of ADAMTS-13 deficiency in TTP, several ADAMTS-13 activity assays have been developed for use in the diagnosis of TTP and/or other microangiopathic disorders. We reviewed the clinical utility of ADAMTS-13 activity testing in suspected TTP, as used in routine clinical practice in a tertiary referral hospital.

METHODS

All requests for ADAMTS-13 activity levels performed at our institution after introduction of the assay were retrospectively audited with respect to clinical diagnosis and results.

RESULTS

In total 57 individual patients were tested, of whom only 46% had a MAHA process. Severe ADAMTS-13 deficiency was present in five TTP patients and in one patient with fulminant hepatic failure.

CONCLUSIONS

Our experience suggests that severely reduced levels are relatively specific for TTP, but may also occur in fulminant hepatic failure. Patients without MAHA may have reduced ADAMTS-13 activity and there is significant overlap in the range of ADAMTS-13 activity seen in non-TTP MAHA diagnoses. This supports the observation that outside the diagnosis and (possible) follow-up of suspected idiopathic TTP, the ADAMTS-13 activity assay has limited clinical utility. Further education about the role of ADAMTS-13 activity testing is needed.

Thrombotic thrombocytopenic purpura secondary to ABO group incompatible blood transfusion in a patient after cardiac surgery

The triggers of secondary thrombotic thrombopcytopenic purpura (TTP) include drug toxicity, radiation and high-dose chemotherapy, angioinvasive infections, surgery and acute graft versus host disease. TTP secondary to surgery have been reported in a number of cases. Most of the cases have been occurred after open heart surgery. Extensive endothelial damage is held responsible as the initiating mechanism in postoperative TTP cases. However, there is no report of secondary TTP describing development owing to ABO incompatible blood transfusion. Here, we describe a patient who developed TTP after transfusion of ABO incompatible blood during hospitalization for bypass surgery. We also propose a hypothesis which may account for the possible underlying mechanism.

Systemic lupus erythematosus and thrombotic thrombocytopenia purpura: a refractory case without lupus activity

The association between systemic lupus erythematosus (SLE) and thrombotic thrombocytopenic purpura (TTP) has been infrequently reported. Usually, patients with TTP have more SLE activity and frequent renal involvement. Here we present a case of TTP associated to low-activity SLE. The absence of renal and major organ involvement increased the difficulty in making the initial diagnosis. ADAMTS13 activity in plasma in this patient was very low, as seen in other similar cases. The evolution of the patient was poor, needing plasma exchanges and immunosuppressive therapy, including the use of rituximab.

The use of monoclonal antibodies in immune-mediated hematologic disorders

In this article, the evidence on the clinical use of monoclonal antibodies in the treatment of immune-mediated hematologic disorders is described. Insights into pathogenic mechanisms have revealed a major role of both B and T cells. Controlled trials have shown conflicting results, necessitating further research regarding pathogenesis, mechanism of action, and resistance. Although the use of more potent and specific monoclonal antibody therapy, mainly targeting costimulation signals, may improve response rates and long-term outcome, its use should be carefully balanced against potential side effects.

ADAMTS13 activity and antigen during therapy and follow-up of patients with idiopathic thrombotic thrombocytopenic purpura: correlation with clinical outcome

BACKGROUND

The assay for ADAMTS13 activity helps clinicians to confirm the clinical diagnosis of idiopathic thrombotic thrombocytopenic purpura. The clinical value of testing for the antigen level of ADAMTS13 protein is, however, less clear.

DESIGN AND METHODS

In this study, both ADAMTS13 antigen and activity levels were measured in 835 sequential samples from 40 consecutive patients who were followed for an average of 29 months throughout the course of acute episode plasma exchange treatment and clinical remission.

RESULTS

During acute episodes, ADAMTS13 activity was severely deficient while ADAMTS13 antigen levels were more variable, ranging from severely deficient to as high as within the reference range. A severe depletion of ADAMTS13 antigen level during acute disease was, however, statistically associated with disease mortality (P=0.0322). For patients who achieved initial clinical responses, ADAMTS13 antigen levels appeared to be restored faster than ADAMTS13 activity to the normal range. Further analysis demonstrated that the ADAMTS13 antigen level at the time of initial clinical recovery was significantly higher in the patients who subsequently achieved a sustained clinical remission than in the group who soon after had an exacerbation (P=0.0187).

CONCLUSIONS

Our data suggest that evaluation of ADAMTS13 antigen levels during the course of therapy and follow-up may offer additional useful information for the management of patients with thrombotic thrombocytopenic purpura.

Anti-CD20 monoclonal antibodies and their use in adult autoimmune hematological disorders

Autoimmune hematological disorders encompass a broad group of hematological conditions characterized by the loss of self-tolerance to a variety of antigens. Despite good response to first-line therapy in the majority of patients, relapses are common, necessitating new and safe therapeutic options. The anti-CD20 monoclonal antibody rituximab has led to substantial improvement in the treatment of malignant and immune-mediated disorders involving B cells. Although experience with rituximab in immune-mediated hematological disorders is rarely supported by randomized trials, there is now substantial experience with rituximab suggesting that anti-CD20 therapy is an effective and well-tolerated alternative to immunosuppressive therapy in these disorders. However, caution is needed based on recent reports describing-sometimes severe-rituximab-related complications.

Thrombotic microangiopathy in haematopoietic cell transplantation: an update

Allogeneic hematopoietic cell transplantation (HCT) represents a vital procedure for patients with various hematologic conditions. Despite advances in the field, HCT carries significant morbidity and mortality. A rare but potentially devastating complication is transplantation-associated thrombotic microangiopathy (TA-TMA). In contrast to idiopathic TTP, whose etiology is attributed to deficient activity of ADAMTS13, (a member of the A Disintegrin And Metalloprotease with Thrombospondin 1 repeats family of metalloproteases), patients with TA-TMA have > 5% ADAMTS13 activity. Pathophysiologic mechanisms associated with TA-TMA, include loss of endothelial cell integrity induced by intensive conditioning regimens, immunosuppressive therapy, irradiation, infections and graft-versus-host (GVHD) disease. The reported incidence of TA-TMA ranges from 0.5% to 75%, reflecting the difficulty of accurate diagnosis in these patients. Two different groups have proposed consensus definitions for TA-TMA, yet they fail to distinguish the primary syndrome from secondary causes such as infections or medication exposure. Despite treatment, mortality rate in TA-TMA ranges between 60% to 90%. The treatment strategies for TA-TMA remain challenging. Calcineurin inhibitors should be discontinued and replaced with alternative immunosuppressive agents. Daclizumab, a humanized monoclonal anti-CD25 antibody, has shown promising results in the treatment of TA-TMA. Rituximab or the addition of defibrotide, have been reported to induce remission in this patient population. In general, plasma exchange is not recommended.

Thrombotic microangiopathy following intestinal transplantation: a single center experience

BACKGROUND

Transplant-related thrombotic microangiopathy (TMA) is a well-recognized complication of all types of transplantations. Despite its known relationship with immunosuppressive therapy, only a few cases have been reported following intestinal transplantation.

METHODS

We retrospectively reviewed the medical files of nine consecutive intestinal transplant patients between 2000 and 2008.

RESULTS

The diagnosis of TMA was established in 3 patients (33%). At diagnosis the immunosuppressive therapy consisted of tacrolimus (n = 3), combined with azathioprine (n = 1) or sirolimus (n = 2) and steroids (n = 2). The median time between transplantation and TMA was 104 days (range, 55-167 days). Levels of ADAMTS13, a von Willebrand protease, were within normal ranges in all 3 patients. Treatment consisted of stopping/tapering of tacrolimus, together with initiation of plasma therapy, leading to complete remission in all 3 patients. During further follow-up, all 3 patients showed severe graft rejection necessitating more profound immunosuppressive therapy, leading to graft loss in 1 patient and infection-related death in the 2 others. At a median follow-up of 52 months (range, 9-100 months) all remaining TMA-free patients (n = 6) were alive with functioning grafts under minimal immunosuppression.

CONCLUSION

Herein we have described 3 intestinal transplant patients who were diagnosed with transplantation-related TMA. Despite excellent disease control the final outcomes were dismal, which clearly contrasts with the outcome among TMA-free patients, who were all well with functioning grafts at last follow-up.

Haptoglobin halts hemoglobin's havoc

Hemoglobin (Hb) is crucial to the function of the red blood cell. However, when it is released during intravascular hemolysis from the cell into blood plasma, it produces a state of NO depletion, oxidant stress, and vascular dysfunction, including hypertension. In their study reported in this issue of the JCI, Boretti and colleagues used canine and guinea pig models to demonstrate that pharmacological doses of glucocorticoid can increase the plasma levels of haptoglobin (Hp), the principal plasma-binding protein for free Hb (see the related article beginning on page 2271). Hp prevented Hb-induced hypertension and the generation of oxidant damage to the kidney. Neutralization of free Hb appears to be part of the downstream antiinflammatory properties of glucocorticoid.

Thrombotic microangiopathy in haematopoietic stem cell transplantation: diagnosis and treatment

Each year in the US, more than 10 000 patients benefit from allogeneic haematopoietic stem cell transplantation (HSCT), a modality that offers an excellent chance of eradicating malignancy but confers a higher risk of treatment-related mortality. An uncommon but devastating consequence of HSCT is transplantation-associated thrombotic microangiopathy (TA-TMA). The incidence of TA-TMA ranges from 0.5% to 76%, with a mortality rate of 60-90% despite treatment. Although there appears to be a consistent treatment approach to idiopathic thrombotic thrombocytopenic purpura (TTP) using plasma exchange, corticosteroids and rituximab, the treatment strategies for TA-TMA are perplexing, in part, because the literature regarding this complex condition does not provide true consensus for incidence, aetiology, diagnostic criteria, classification and optimal therapy. The classic definition of idiopathic TTP includes schistocytes on the peripheral blood smear, thrombocytopenia and increased serum lactate dehydrogenase. Classic idiopathic TTP has been attributed to deficient activity of the metalloproteinase responsible for cleaving ultra-large von Willebrand factor multimers. This protease is a member of the 'a disintegrin and metalloprotease with thrombospondin type 1 motif' family and is subsequently named ADAMTS-13. Severely deficient ADAMTS-13 activity (<5% of normal) is associated with idiopathic TTP in 33-100% of patients. In constrast to the pathophysiology of idiopathic TTP, patients with TA-TMA have >5% ADAMTS-13 serum activity. These data may explain why plasma exchange, a standard treatment modality for idiopathic TTP that restores ADAMTS-13 activity, is not effective in TA-TMA. TA-TMA has a multifactorial aetiology of endothelial damage induced by intensive conditioning therapy, irradiation, immunosuppressants, infection and graft-versus-host disease. Treatment consists of substituting calcineurin inhibitors with an alternative immunosuppressive agent that possesses another mode of action. One candidate may be daclizumab, especially in those with mild to moderate TMA. Rituximab therapy or the addition of defibrotide may also be beneficial. In general, plasma exchange is not recommended.

Thrombotic thrombocytopenic purpura related to severe ADAMTS13 deficiency in children

Thrombotic thrombocytopenic purpura (TTP) related to a severely deficient activity of the von Willebrand factor cleaving protease, ADAMTS (A Disintegrin And Metalloprotease with ThromboSpondin type 1 repeats) 13, is a life-threatening event, the onset of which may occur as early as childhood. TTP is either inherited (Upshaw-Schulman syndrome) via ADAMTS13 gene mutations (neonatal onset) or acquired via anti-ADAMTS13 autoantibodies (childhood onset). TTP is due to platelet- and von-Willebrand-factor-rich thrombi of the microvasculature, inducing mechanical hemolytic anemia, consumption thrombocytopenia, and multivisceral ischemia. Clinical course consists of relapsing acute events triggered mostly by infections, associated icterus and hyperbilirubinemia, severe hemolytic anemia with schistocytosis and a negative Coombs test, severe thrombocytopenia, and sometimes symptoms related to visceral ischemia (renal failure, central nervous system vascular events, other organ failure). The recently available ADAMTS13 laboratory investigation combining measurement of ADAMTS13 activity in plasma, search for an ADAMTS13 circulating inhibitor, and anti-ADAMTS13 IgG and ADAMTS13 gene sequencing is a crucial addition to TTP diagnosis. Plasma exchanges are first-line treatment of acquired TTP, combined with steroids and immunosuppressive drugs. Curative treatment of acute events in Upshaw-Schulman syndrome relies on plasma infusions (provider of active ADAMTS13). Guidelines for preventive treatment of relapses are not clearly established but should associate plasmatherapy and caution to triggers of relapses. Therapeutic perspectives are focused on the development of concentrated plasma-derived ADAMTS13 or recombinant ADAMTS13.

New treatment options for immune-mediated hematological disorders

In recent years, there has been a tremendous increase in the number of clinical studies with monoclonal antibodies and small molecules in the treatment of hematological malignancies. Clinical observations have shown that some of these molecules may also aid in the treatment of immune-mediated hematological disorders. Moreover, immunotherapy has become an important treatment cornerstone in other, non-hematological, auto-immune diseases. This paper reviews the current state of the use of these new molecules in the treatment of the most frequently encountered immune-mediated hematological disorders: auto-immune hemolytic anemia (AIHA), idiopathic thrombocytopenic purpura (ITP), and thrombotic thrombocytopenic purpura (TTP).

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.

Relationship between ADAMTS13 activity in clinical remission and the risk of TTP relapse

Idiopathic thrombotic thrombocytopenic purpura (TTP) is characterized by frequent recurrences. Effective screening for relapses will enable intervention prior to overt episodes of TTP. The present study used a modified assay to detect ADAMTS13 (a disintegrin and metalloprotease with thrombospondin type 1 motif, 13) activity as low as 0.5%. This analytical improvement permits adequate measurement of ADAMTS13 activity levels in 97% of remission samples used for statistical modelling. ADAMTS13 activity and ADAMTS13 antibody (IgG) were measured in 157 serial samples prospectively collected from 24 TTP patients during periods of clinical remission. These patients were followed-up quarterly for an average of 23 months, during which time nine episodes of TTP relapse occurred among six patients. Finally, logistic regression modelling was used to define the relationship between ADAMTS13 activity levels (0.5-100%) and the probability of TTP relapses. Our data demonstrated that lower ADAMTS13 activity and younger age were significantly associated with higher risk of relapse in the 3 months after specimens were taken. In contrast, ADAMTS13 antibody IgG levels were not predictive of TTP relapses. Identification of low ADAMTS13 activity during clinical remission as a key risk factor for TTP relapses provides a new screening strategy to identify patients who may benefit from prophylactic therapy prior to disease relapses.

Diagnosis and treatment of transplantation-associated thrombotic microangiopathy: real progress or are we still waiting?

Transplantation-associated thrombotic microangiopathy (TA-TMA) is an infrequent but devastating syndrome that occurs in allogeneic hematopoietic stem cell transplant recipients, and is associated with a variety of transplantation-related factors, including conditioning regimens, immunosuppressive agents, GVHD and opportunistic infections. Progress in managing this condition has been hampered by lack of a consensus definition and poor understanding of the pathophysiology of the disorder. Two different groups recently have proposed consensus definitions, yet they fail to distinguish the primary syndrome from the secondary causes, such as a variety of infections, medication exposure or other conditions. Increasing evidence suggests that TA-TMA is a multifactorial disorder that is distinct from thrombotic thrombocytopenic purpura (TTP), and likely represents the final common pathway of a number of endothelial cell insults. TA-TMA responds poorly to conventional treatment for TTP, including plasma exchange, but newer agents, including daclizumab and defibrotide show promise. In addition, other agents known to modify endothelial responses to injury, including statins, prostacyclin analogues, endothelin-receptor antagonists and free radical scavengers, may lead to improved outcomes for patients affected by this disorder.