Abnormalities of von Willebrand factor multimers in drug-associated thrombotic microangiopathies

The Link Between Conventional and Novel Anti-Cancer Therapeutics with Thrombotic Microangiopathy

BACKGROUND

Kidney disease associated with cancer and anti-cancer therapies has been increasingly recognized in the field of onco-nephrology. In particular, drug-induced nephrotoxicity has important implications since most chemotherapeutic agents have a nephrotoxic potential. Also, standard creatinine clearance methods used for the measurement of kidney function have been questioned in cancer patients due to factors like low muscle mass and poor nutritional status. Overestimations of the glomerular filtration rate, not only can increase the nephrotoxic potential of different agents, but also further limit the use of first-line therapies.

OBJECTIVE

This review covers specifically the drug-induced thrombotic microangiopathy and its two pathophysiologic mechanisms which include immune or idiosyncratic reactions, and non-immune or dose-dependent ones.

CONCLUSION

As novel cancer therapies are developed, it is paramount to pursue a better understanding of conventional and novel chemotherapeutic agents and their role in kidney disease.

Thromboembolism in Cancer Patients: Pathogenesis and Treatment

In this review we summarize the causes of cancer related thrombosis as well as modern treatment approaches. Malignancy as a risk factor for thromboembolism is becoming increasingly recognized by clinicians caring for these patients. The probability of thrombosis occurring in an individual patient is dependent on several factors, including accompanying medical problems, the type of cancer, the clinical stage, performance status, and the treatment modalities employed. Thrombophilia with a history of thromboembolism is important as well. The overall risk of thrombosis is sevenfold that of noncancer patients. Though much has been learned about the pathogenesis of cancer-related thrombosis, we are in fact just beginning to understand the cross-talk between cancer cells and their related microenvironment, and such investigations are likely to increase our knowledge of cancer-related thrombosis mechanisms. Research in these areas may also suggest new strategies for cancer prevention, metastasis suppression, and new treatments. Drugs used in cancer therapy are increasingly recognized to directly contribute to the thrombotic tendency. Few studies provide data on the optimal management of cancer patients with thrombosis. It has been learned that retreating with the same drug can be very hazardous. In general the approach to prevention of thrombosis is the same as for noncancer patients, recognizing that specific cancer types and stage can place a patient in a high-risk category. Initial coumadin therapy fails in a significant number of patients with cancer. Recognition of the cancer patients at highest risk for coumadin failure is challenging. Low-molecular-weight heparins appear to be more effective in such situations where coumadin is likely to fail or has failed, but these drugs are thought to be costlier. Newer agents such as Factor Xa inhibitors and TF inhibitors are currently under investigation and may be found useful in the management of cancer-related thrombosis.

Thrombotic microangiopathy, cancer, and cancer drugs

Thrombotic microangiopathy (TMA) is a complication that can develop directly from certain malignancies, but more often results from anticancer therapy. Currently, the incidence of cancer drug-induced TMA during the last few decades is >15%, primarily due to the introduction of anti-vascular endothelial growth factor (VEGF) agents. It is important for clinicians to understand the potential causes of cancer drug-induced TMA to facilitate successful diagnosis and treatment. In general, cancer drug-induced TMA can be classified into 2 types. Type I cancer drug-induced TMA includes chemotherapy regimens (ie, mitomycin C) that can potentially promote long-term kidney injury, as well as increased morbidity and mortality. Type II cancer drug-induced TMA includes anti-VEGF agents that are not typically associated with cumulative dose-dependent cell damage. In addition, functional recovery of kidney function often occurs after drug interruption, assuming a type I agent was not given prior to or during therapy. There are no randomized controlled trials to provide physician guidance in the management of TMA. However, previously accumulated information and research suggest that endothelial cell damage has an underlying immunologic basis. Based on this, the emerging trend includes the use of immunosuppressive agents if a refractory or relapsing clinical course that does not respond to plasmapheresis and steroids is observed.

Cancer-related coagulopathies

The association between cancer and thrombosis is known for years. Besides the well-recognized connection between venous thromboembolism and malignancies, there are, however, also other manifestations of cancer-related activation of coagulation and (micro)vascular dysfunction. In fact, coagulation derangements and vascular disturbances in patients with cancer cover a wide spectrum of diseases and various clinical manifestations. In this review we will highlight the mechanisms that play a role in the systemic activation of coagulation in cancer patients, in its most severe form manifested as disseminated intravascular coagulation. Clinically, disseminated intravascular coagulation (DIC) in cancer has in general a less fulminant presentation than the types of DIC complicating sepsis and trauma. A more gradual, but also more chronic, systemic activation of coagulation can proceed subclinically. The relationship between venous thromboembolism and cancer as a consequence of the hypercoagulability will be discussed as well. Furthermore, the role of perturbed endothelium in the pathogenesis of microvascular dysfunction and microangiopathy in particular in the setting of cancer and chemo- or radiotherapy will be reviewed.

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.

Prospective study on the behaviour of the metalloprotease ADAMTS13 and of von Willebrand factor after bone marrow transplantation

Thrombotic microangiopathies (TMAs) are rare but serious complications of bone marrow transplantation (BMT). Clinical manifestations are similar to those of thrombotic thrombocytopenic purpura (TTP), but prognosis is generally poorer despite plasma exchange. The enzymatic activity of the plasma metalloprotease ADAMTS13, which cleaves ultralarge thrombogenic multimers of von Willebrand factor (VWF) derived from activated endothelial cells, is very low or undetectable in patients with classic TTP, and protease deficiency is thought to play a mechanistic role in the formation of platelet thrombi in the microcirculation. This is the first prospective study to evaluate the incidence of TMA in 46 consecutively recruited patients undergoing autologous or allogeneic BMT and explore in parallel the behaviour of ADAMTS13, VWF antigen and VWF multimer size. The incidence of post-BMT TMA was 6% (three of 46); all cases occurred after allogeneic BMT. Compared with baseline values plasma ADAMTS13 activity was significantly reduced in patients undergoing BMT, particularly after the conditioning regimen (mean values: 50 +/- 22 vs. 77 +/- 32%; P < 0.0001). In the three patients who developed TMA, ADAMTS13 decreased after conditioning, but was very low in one case only (8%). VWF antigen levels progressively increased after the conditioning regimen (228 +/- 75 vs. 178 +/- 76% at baseline, P = 0.002). The mean proportion of high-molecular weight VWF multimers did not change in the various stages of BMT, even though ultralarge multimers were transiently found in same cases with and without TMA. Hence, the measurements evaluated in this study are not clinically useful to predict the occurrence of post-BMT TMA.

Vascular Toxicity of Antineoplastic Agents

Among the various deleterious effects of cancer chemotherapy, vascular toxicity is the least well recognized. This lack of recognition may be because the vasculotoxic phenomena are not unique to antineoplastic agents, can occur in patients without exposure to these agents, and the fact cancer itself may produce a hypercoagulable state. As a result, many vascular events either go unnoticed, are ignored, and/or are attributed to the underlying malignancy. Many antineoplastic therapies are associated with various vascular phenomena that range from simple phelibitis to lethal microangiopathy. Recognition of these events is important to minimize the morbidity and even prevent unnecessary deaths. Herein we review the vascular syndromes that have been reported in association with antineoplastic agents.

von Willebrand factor, ADAMTS-13, and thrombotic thrombocytopenic purpura

Thrombotic thrombocytopenic purpura (TTP) is a severe, occlusive, microvascular "thrombotic microangiopathy" characterized by systemic platelet aggregation, organ ischemia, profound thrombocytopenia, and erythrocyte fragmentation. Failure to degrade "unusually large" (UL) von Willebrand factor (VWF) multimers as they are secreted from endothelial cells probably causes most cases of familial TTP, acquired idiopathic TTP, thienopyridine-related TTP, and pregnancy-associated TTP. The emphasis in this review is the pathophysiology of familial and acquired idiopathic TTP. In each of these entities, there is a severe defect in the function of a plasma enzyme, VWF-cleaving metalloprotease (ADAMTS-13), that normally cleaves hyper-reactive ULVWF multimers into smaller and less adhesive VWF forms. In familial TTP, mutations in the ADAMTS13 gene cause absent or severely reduced plasma VWF-cleaving metalloprotease activity. Acquired idiopathic TTP, in contrast, is the result in many patients of the production of autoantibodies that inhibit the function of ADAMTS-13. Established, evolving, and some of the unresolved issues in TTP pathophysiology will be summarized.

Predicting response to plasma exchange in patients with thrombotic thrombocytopenic purpura with measurement of vWF-cleaving protease activity

BACKGROUND

Severe deficiency of vWF-cleaving protease (vWF-CPase) activity was recently found in patients with thrombotic thrombocytopenic purpura (TTP). Although the survival of patients with TTP has been dramatically improved with plasma exchange (PE), there are still many patients who are refractory to PE and immunosuppressive therapy.

STUDY DESIGN AND METHODS

The activities of vWF-CPase and its inhibitor were measured in 27 patients with nonfamilial TTP and hemolytic-uremic syndrome (HUS) to examine the relationship between the clinical variables and vWF-CPase activity.

RESULTS

Eight of nine patients with HUS had more than 40 percent of vWF-CPase activity, whereas one had 28 percent of the normal level at the acute phase. Ten of 12 TTP patients with a good outcome had a severe deficiency of vWF-CPase activity and its inhibitor, whereas four of six patients with a poor outcome had a moderate deficiency of vWF-CPase activity along with a lack of the inhibitor. PE produced normalization of the vWF-CPase activity and neutralization of the inhibitor in TTP patients with a good outcome; however, some TTP patients with vWF-CPase inhibitor had relapsed and required an immunosuppressive therapy. The response to the combination therapy with PE and immunosuppressive treatment was poor in TTP patients without a severe deficiency of vWF-CPase activity.

CONCLUSION

Assays of vWF-CPase activity and its inhibitor may be useful for predicting the response to therapy and the outcome of patients with TTP. In some patients, nonfamilial TTP with a poor prognosis may not be caused by a constitutional or acquired deficiency of vWF-CPase with its inhibitor. Although PE and immunosuppressive therapy are effective in patients with nonfamilial TTP and a vWF-CPase inhibitor, other therapeutic modalities may be needed for nonfamilial TTP with unknown etiology.

Thrombotic thrombocytopenic purpura: the systemic clumping "plague"

In thrombotic thrombocytopenic purpura (TTP), a multimeric form of von Willebrand factor (vWf) that is larger than ordinarily found in the plasma causes systemic platelet aggregation under the high-shear conditions of the microcirculation. A divalent cation-activated, vWf-cleaving metalloprotease that metabolizes large vWf multimers to smaller forms in normal plasma is severely reduced or absent in most patients with TTP. The vWf-cleaving metalloprotease either is not produced or is defective in children with chronic relapsing TTP. When the enzyme is provided by the infusion of normal plasma, these patients remain free of TTP symptoms for about three weeks. An IgG autoantibody to the vWf-cleaving metalloprotease is found transiently in many adult patients with acute idiopathic, recurrent, and ticlopidine/clopidogrel-associated TTP. These patients require plasma exchange, i.e., concurrent replacement of the inhibited vWf-cleaving metalloprotease by plasma infusion and plasmapheresis. The vWf-cleaving metalloprotease is present in fresh-frozen plasma, in cryoprecipitate-depleted plasma (cryosupernatant), and in plasma that has been treated with solvent and detergent. The pathophysiology of platelet aggregation in bone marrow transplantation/chemotherapy-associated thrombotic microangiopathy, and in the hemolytic-uremic syndrome, is not established. In neither condition is there a severe decrease in plasma vWf-cleaving metalloprotease activity.

Therapeutic apheresis for cancer related hemolytic uremic syndrome

Hemolytic uremic syndrome (HUS) can be seen as a result of disseminated cancer, as a consequence of chemotherapy, or in association with bone marrow transplantation (BMT). Further distinction can be made when the clinical presentation is that of an acute, fulminant course with rapidly progressive renal failure or that of a sub-acute form with a slow progression of renal involvement. Each of the different etiologies (cancer, chemotherapy, or BMT) and each of the two basic clinical presentations has its own prognosis. There are no randomized, controlled studies to elucidate the role of therapeutic apheresis for cancer-related HUS. Hemolytic uremic syndrome related to disseminated cancer is most often a terminal event and is not commonly treated with apheresis procedures, although there are anecdotal reports that plasma exchange may be beneficial. Chemotherapy and drug-related HUS have a prognosis that is strongly dependent on the severity of the presentation, but even in the most severe cases may respond to either immunoadsorption or plasma exchange with fresh frozen plasma (FFP). Finally, BMT-related HUS has a poor prognosis but may respond to immunoadsorption, plasma exchange, or a combination of the two.

Extracorporeal treatment of thrombotic microangiopathy: a ten year experience

We reviewed 24 episodes of thrombotic microangiopathy (TMA) representing 22 patients from July 1989 to July 1998. Nine cases presented with a community acquired (CA group) thrombotic thrombocytopenic purpura or hemolytic uremic syndrome (TTP/HUS), 3 cases were related to pregnancy (P group), 10 cases were compatible with TMA after bone marrow transplantation or chemotherapy (BMT/C group), and 2 cases had a background of scleroderma (SC group). Twenty episodes were treated exclusively with therapeutic plasma exchange (TPE) using fresh frozen plasma (FFP) replacement. In the BMT/C group, 4 patients underwent immunoadsorption with the Prosorba protein A column in addition to TPE. The CA, P, and SC groups had favorable outcomes with 78% (7 of 9), 100% (3 of 3), and 100% (2 of 2) survival, respectively. Despite intensive therapy, there was only 1 survivor in the BMT/C group (1 of 10). Successful outcome required up to 57 TPE treatments. We could not document any benefit to immunoadsorption with the Prosorba protein A column.

Vasculopathy of small muscular arteries in pediatric patients after bone marrow transplantation

Bone Marrow Transplant (BMT) is a critical therapeutic intervention for a variety of diseases occurring in the pediatric patient. Complications of allogeneic BMT include graft-versus-host disease (GVHD), infection, drug toxicity, thrombotic microangiopathy, and veno-occlusive disease. With solid organ transplantation, chronic vascular rejection has emerged as a major factor limiting long-term survival of the graft. We present a vasculopathy of small muscular arteries in 6 patients after allogeneic BMT. Cases include 4 boys and 2 girls ranging in age from 4 months to 13 years with full or partial human leukocyte antigen matching. Five of the 6 transplants were from related donors. The vasculopathy occurred 13 to 418 days after transplant and was noted in surgical specimens (2) and at autopsy (4). It was seen in the gastrointestinal tract and lung in 3 cases each. Vascular changes in small muscular arteries include concentric intimal or medial hyperplasia with luminal narrowing, prominent myxoid change, extravasated red blood cells, and presence of some foamy histiocytes with no evidence of thrombotic microangiopathy. Vasculopathy contributed to intestinal compromise requiring surgical intervention 3 times in 1 patient, and diffuse alveolar damage with hemorrhage in another. All 6 patients are dead. The cause of this unusual vasculopathy present in patients after BMT is likely to be multifactorial, involving effects of irradiation, chemotherapy, cyclosporine, and GVHD. Together these may create a negative synergy which produces an obliterative arteriopathy that should be recognized as a pathological entity and may be a harbinger of a poor prognosis.

Cancer chemotherapy-related thrombotic thrombocytopenic purpura: biological evidence of increased nitric oxide production

The occurrence of thrombotic thrombocytopenic purpura (TTP) in cancer patients receiving chemotherapy has been well established; although this entity is rare, its clinical importance seems to be growing. We describe 3 cases of TTP developing in cancer patients receiving different chemotherapeutic regimens. Using a sensitive high-performance liquid chromatographic method, we evaluated the stable nitric oxide end products, nitrite and nitrate, in the plasma of these patients. Nitric oxide is one of the key components involved in maintaining the normal nonthrombogenicity of the vascular endothelium. In our 3 patients, we found increased nitrate titers that were substantially higher than those observed in patients with de novo TTP. The observed increased release of nitrate could be interpreted as the consequence of massive disruption of endothelial integrity, with consequent passive nitric oxide release in vivo, or an adaptive mechanism of the endothelium to compensate for diffuse microvascular occlusion. The 2 mechanisms may both be involved, but the normal titers of nitric oxide end products in de novo TTP suggest that the former mechanism is more important, at least in cancer chemotherapy-related TTP.

von Willebrand factor-cleaving protease in thrombotic thrombocytopenic purpura and the hemolytic-uremic syndrome

BACKGROUND

Thrombotic thrombocytopenic purpura and the hemolytic-uremic syndrome are severe microvascular disorders of platelet clumping with similar signs and symptoms. Unusually large multimers of von Willebrand factor, capable of agglutinating circulating platelets under high shear stress, occur in the two conditions. We investigated the prevalence of von Willebrand factor-cleaving protease deficiency in patients with familial and nonfamilial forms of these disorders.

METHODS

Plasma samples were obtained from 53 patients with thrombotic thrombocytopenic purpura or hemolytic-uremic syndrome. Von Willebrand factor-cleaving protease was assayed in diluted plasma samples with purified normal von Willebrand factor as the substrate. The extent of the degradation of von Willebrand factor was assessed by electrophoresis in sodium dodecyl sulfate-agarose gels and immunoblotting. To determine whether an inhibitor of von Willebrand factor-cleaving protease was present, we measured the protease activity in normal plasma after incubation with plasma from the patients.

RESULTS

We examined 30 patients with thrombotic thrombocytopenic purpura and 23 patients with the hemolytic-uremic syndrome. Of 24 patients with nonfamilial thrombotic thrombocytopenic purpura, 20 had severe and 4 had moderate protease deficiency during an acute event. An inhibitor found in 20 of these patients was shown to be IgG in five of five tested plasma samples. Of 13 patients with nonfamilial hemolytic-uremic syndrome, 11 had normal levels of activity of von Willebrand factor-cleaving protease during the acute episode, whereas in 2 patients, the activity was slightly decreased. All 6 patients with familial thrombotic thrombocytopenic purpura lacked von Willebrand factor-cleaving protease activity but had no inhibitor, whereas all 10 patients with familial hemolytic-uremic syndrome had normal protease activity. In vitro proteolytic degradation of von Willebrand factor by the protease was studied in 5 patients with familial and 7 patients with nonfamilial hemolytic-uremic syndrome and was normal in all 12 patients.

CONCLUSIONS

Nonfamilial thrombotic thrombocytopenic purpura is due to an inhibitor of von Willebrand factor-cleaving protease, whereas the familial form seems to be caused by a constitutional deficiency of the protease. Patients with the hemolyticuremic syndrome do not have a deficiency of von Willebrand factor-cleaving protease or a defect in von Willebrand factor that leads to its resistance to protease.

Acquired Deficiency of von Willebrand Factor-Cleaving Protease in a Patient With Thrombotic Thrombocytopenic Purpura

Plasma of patients with thrombotic thrombocytopenic purpura (TTP) has been shown to contain unusually large von Willebrand factor (vWF) multimers that may cause platelet agglutination in vivo. Fresh frozen plasma infusions and plasma exchange represent the most efficient therapy of acute TTP. A specific protease responsible for cleavage of vWF multimers has been recently isolated from normal human plasma and was found to be deficient in four patients with chronic relapsing TTP. We examined the activity of the vWF-cleaving protease in plasma samples collected over a period of 400 days from a further patient with recurrent episodes of TTP who was treated by plasma exchange, plasma infusion, vincristine, corticosteroid therapy, and splenectomy. Complete deficiency of the vWF-cleaving protease was established during the first episode of TTP. The ensuing normalization of the platelet count was associated with the appearance of the protease activity. Three months after remission from the initial TTP event, the vWF-cleaving protease again disappeared and the platelet count gradually decreased. Relapses of severe thrombocytopenia occurred 7 and 11 months after the first acute episode of TTP. Deficient protease activity was associated with the presence in the patient plasma of an inhibitor that was found to be an IgG. Plasma exchange/infusion was followed by a temporary increase in the antibody titer, whereas treatment with vincristine led to a recovery of the platelet count without affecting the inhibitor concentration. Splenectomy and corticosteroid treatment resulted in disappearance of the autoantibody and normalization of the protease activity and of the platelet count. Our data suggest that the thrombocytopenia in this patient with TTP was associated with a lack of the vWF-cleaving protease activity depleted by an autoimmune mechanism. This case, together with our previously reported patients, leads us to conclude that acquired as well as constitutional deficiency of the vWF-cleaving protease may predispose to TTP.

Protein A-immunoadsorption in chemotherapy associated hemolytic-uremic syndrome

Circulating IgG-immune complexes (IgG-IC) play a role in the complex etiology of C-HUS. In an ongoing open clinical study protein A immunoadsorption treatment is carried out for patients who developed severe forms of the syndrome after mitomycin-C chemotherapy. So far, successful treatment of 14 out of 19 evaluable patients was possible. A protein A immunoadsorption system was used, allowing processing of large plasma volumes to eliminate IgG and IgG-IC from the patient's plasma.

Deficient Activity of von Willebrand Factor–Cleaving Protease in Chronic Relapsing Thrombotic Thrombocytopenic Purpura

In patients with thrombotic thrombocytopenic purpura (TTP), excessive intravascular platelet aggregation has been associated with appearance in plasma of unusually large von Willebrand factor (vWF ) multimers. These extremely adhesive vWF multimers may arise due to deficiency of a “depolymerase” cleaving vWF to smaller molecular forms, either by reducing the interdimeric disulfide bridges or by proteolytic degradation. We studied the activity of a recently described vWF-cleaving protease in four patients with chronic relapsing TTP. Diluted plasma samples of TTP patients were incubated with purified normal human vWF in the presence of a serine protease inhibitor, at low ionic strength, and in the presence of urea and barium ions. The extent of vWF degradation was assayed by electrophoresis in sodium dodecyl sulfate-agarose gels and immunoblotting. Four patients, that included two brothers, with chronic relapsing TTP displayed either substantially reduced levels or a complete absence of vWF-cleaving protease activity. In none of these patient plasmas was an inhibitor of or an antibody against the vWF-cleaving protease established. Our data suggest that the unusually large vWF multimers found in TTP patients may be caused by deficient vWF-cleaving protease activity. Deficiency of this protease may be inherited in an autosomal recessive manner and seems to predispose to chronic relapsing TTP. The assay of the vWF-cleaving protease activity may be used as a sensitive diagnostic tool for identification of subjects with a latent TTP tendency.

Cyclosporine-induced detachment of vascular endothelial cells initiates the intrinsic coagulation system in plasma and whole blood

Cyclosporine A (CsA) is supposed to alter the metabolism of vascular endothelial cells, leading to a prothrombotic state. We examined by which mechanism human umbilical vein endothelial cells (HUVECs) treated with CsA would promote coagulation in human plasma and in whole blood. Treatment of HUVECs with CsA at concentrations clinically used led to dose-dependent cell detachment, with the subsequent exposure of the highly procoagulant connective tissue. As determined by scanning electron microscopy, cell counting of detached and adherent cells, and antigenic measurement of collagen exposure, HUVECs treated with 0.4 micrograms/ml CsA (or more) for 4 days exhibited significant amounts of subendothelial areas. On CsA-treated HUVEC monolayers, the clotting time of recalcified citrated platelet-rich plasma (PRP), but not platelet-poor plasma (PPP), was dose-dependently shortened. Likewise, the onset of thrombin generation was significantly earlier. Except at a high concentration of 8.0 micrograms/ml CsA, there was no procoagulant effect when PPP was used. To investigate CsA-treated HUVECs in whole blood, cells were cultivated on globular microcarriers and were incubated with nonanticoagulated whole blood. When untreated cells were used, generation of factor Xa, thrombin, and kallikrein was completely suppressed for 30 minutes. HUVEC beads treated with 0.4 and 0.8 micrograms/ml CsA, however, led to a dose-dependent generation of all three coagulation factors, with peak values at 2.5 to 5 minutes. Extrinsic activation was excluded, since CsA treatment did not induce tissue factor activity in HUVECs. Furthermore, the thrombomodulin activity of HUVECs w as not altered by CsA. In conclusion, treatment of HUVECs with CsA for 4 days at concentrations clinically used leads to the exposure of subendothelial areas that induce activation of the intrinsic coagulation in recalcified PRP and nonanticoagulated whole blood.

Thrombotic microangiopathies associated with drugs and bone marrow transplantation

This type of thrombotic microangiopathy more commonly resembles the hemolytic-uremic syndrome (HUS) than thrombotic thrombocytopenic purpura (TTP). The syndrome has been associated with the use of cyclosporin, mitomycin C, combinations of other chemotherapeutic and immunosuppressive agents, and total body irradiation. Endothelial cell injury and von Willebrand factor may be involved in pathogenesis of the intravascular platelet aggregation and tissue (especially renal) ischemia and infarction that characterize the entity. The most effective therapy for thrombotic microangiopathy associated with drugs and bone marrow transplantation has not been determined.

Apheresis in grade 4 bone marrow transplant associated thrombotic microangiopathy: a case series

Bone marrow transplant-associated thrombotic microangiopathy (BMT-TM) ranges in severity from a self-limited to a fatal disorder. There has been no specific therapy for this condition. We have previously described a clinical grading system for BMT-TM, based upon lactate dehydrogenase level (LDH) and percentage fragmented cells (FC) as follows: grade 0, normal or increases LDH and % FC < or = to 1.2%; grade 1, normal LDH and FC > or = to 1.3%; grade 2, increases LDH and FC = 1.3-4.8%; grade 3, increases LDH and FC = 4.9-9.6%; and grade 4, increases LDH and FC > or = to 9.7%. Patients with grade 4 BMT-TM usually have fulminant disease and generally succumb. This study summarizes results using a variety of apheresis procedures in a series of 16 patients with grade 4 BMT-TM. The apheresis procedures consisted of plasma exchange (with replacement with fresh frozen plasma or cryo-poor plasma), and protein A immunoadsorption (PAI). The PAI exchanges were not done concurrently with plasma exchange procedures. Fifteen patients had undergone an allogeneic BMT and the 16th patient had undergone an autologous peripheral blood stem cell transplant. Half showed hematologic improvement with a downstaging of their TM to grades 1-3. All non-responders died a median of 11 days following the onset of grade 4 BMT-TM. The median survival in the responders was significantly (P = 0.001) increased to 218 days with three responders surviving more than 400 days following the onset of this severe complication. These results suggest a role for apheresis in the treatment of this lethal complication. Nevertheless grade 4 BMT-TM represents a major complication of BMT; the median survival in this group of 16 patients with grade 4 BMT-TM was only 31 days.

Abnormally large von Willebrand factor multimers in Henoch-Schönlein purpura

Allergic vasculitis phenomena seem to be involved in Henoch-Schönlein purpura (HSP). Elevated plasma levels of von Willebrand factor (vWf) are a well recognized feature of vasculitis and have been taken as an indication of in vivo endothelial cell damage. Plasma factor VIII:C and vWf levels and vWf multimeric pattern were studied in 8 patients with HSP, during active disease and twice during the remission (3 and 9 months later). Plasma vWf multimeric composition was evaluated using low resolution gels which better resolve large vWf multimers. During active disease plasma factor VIII:C, vWf:Ag, and vWf:RCoF were normal in 5% of patients and increased in three, but in each patient, platelets appeared to aggregate at doses of ristocetin lower than in normals. Furthermore, all patients demonstrated the presence of abnormally large vWf multimers usually found only in platelets and endothelial cells. Three and 9 months later, during remission, in spite of the normalization of factor VIII:C and vWf levels, the abnormal multimers were still detectable, as well as hyper-responsiveness to ristocetin. These findings confirm that damage and/or perturbation of endothelial cells is associated with HSP. Moreover, the persistence of abnormality in the vWf multimeric pattern, when the disease is inactive, suggests that the mechanisms involved operate through the entire clinical course.