Diclofenac-induced thrombotic thrombocytopenic purpura with concomitant complement dysregulation: a case report and review of the literature.

BACKGROUND: Thrombotic thrombocytopenic purpura and hemolytic uremic syndrome are two forms of thrombotic microangiopathies. They are characterized by severe thrombocytopenia, microangiopathic hemolysis, and thrombosis, leading to a systemic inflammatory response and organ failure. Plasmapheresis is used to treat thrombotic microangiopathies. A different entity known as atypical hemolytic uremic syndrome has garnered more clinical recognition because reported cases have described that it does not respond to standard plasmapheresis. Diclofenac potassium is a non-steroidal anti-inflammatory drug that is used to treat pain. CASE REPORT: A 35-year-old Hispanic man presented to our emergency department with complaints of generalized malaise, fever, and an evanescent skin rash. During admission, he reported the use of diclofenac potassium for back pain on a daily basis for 1 week. He was noted to have peripheral eosinophilia, so he was admitted for suspected drug reaction involving eosinophilia and systemic symptoms. His initial laboratory work-up showed microangiopathic hemolytic anemia and thrombocytopenia. He also experienced a seizure, encephalopathy, and had a PLASMIC score of 7, thus raising concerns for thrombotic thrombocytopenic purpura. He underwent emergent plasmapheresis, which improved his clinical condition. The diagnosis was confirmed by assessing the levels of disintegrin and metalloproteinase with thrombospondin type 1 motif, member 13, which was less than 3%. In addition, his skin biopsy was positive for patchy complement deposition, demonstrating complement dysregulation. CONCLUSION: Thrombotic thrombocytopenic purpura is a rare condition that can be acquired. Our case is rare because it represents the first report of diclofenac potassium-induced thrombotic thrombocytopenic purpura with subjacent complement activation and dysregulation. Early recognition and aggressive management led to a favorable outcome.

Maintenance rituximab for relapsing thrombotic thrombocytopenic purpura: a case report.

BACKGROUND: Appropriate management to prevent relapses of acquired, autoimmune thrombotic thrombocytopenic purpura (TTP) is not clear. Rituximab (375 mg/m2 /week × 4) is effective treatment for acute episodes but it is not consistently effective for prevention of relapses. Maintenance rituximab, 375 mg/m2 /3 months for 2 years, is commonly used to prevent progression of follicular lymphoma, but the outcome of maintenance rituximab to prevent TTP relapses has been rarely reported. CASE REPORT: An 8-year-old girl was diagnosed with acquired TTP in 2008; her ADAMTS13 activity was less than 5%, with a functional inhibitor of greater than 8 Bethesda units/mL. She achieved remission with therapeutic plasma exchange, corticosteroids, and rituximab (375 mg/m2 /week × 4). During the following 6 years she had seven additional episodes. Each episode responded to therapeutic plasma exchange, sometimes requiring additional treatments (corticosteroids, rituximab, and cyclophosphamide). However, these treatments, as well as splenectomy and trials of cyclophosphamide and mycophenolate mofetil during clinical remissions, failed to prevent relapses. Her ADAMTS13 activity remained 8% or less throughout all of her remissions. Maintenance rituximab was begun in 2013: 500 mg (313 mg/m2 ) every 2-3 months × 5, then 600 mg (375 mg/m2 ) every 6 months × 2. After 1 year, her ADAMTS13 was 26%; after 2 years, 51%. During the past 3 years since stopping rituximab, she has remained well, with normal ADAMTS13 activity (70%-78%). CONCLUSION: Maintenance rituximab treatment may be effective for prevention of relapses in patients with acquired, autoimmune TTP, even when splenectomy and intensive immunosuppression, including multiple conventional courses of rituximab, fail to prevent subsequent relapses.

Complement activation associated with ADAMTS13 deficiency may contribute to the characteristic glomerular manifestations in Upshaw-Schulman syndrome.

INTRODUCTION: Upshaw-Schulman syndrome (USS) is a congenital form of thrombotic thrombocytopenic purpura (TTP) associated with loss-of-function mutations in the ADAMTS13 gene, possibly leading to aberrant complement activation and vascular injury. However, USS is extremely rare, and there have been no systematic studies correlating histopathological severity with local ADAMTS13 expression and complement activation. MATERIALS AND METHODS: Here, we compared histopathological features, ADAMTS13 immunoreactivity, and immunoreactivity of complement proteins C4d and C5b-9 among renal biopsy tissues from five USS cases, ten acquired TTP cases, and eleven controls. RESULTS: Pathological analysis revealed chronic glomerular sclerotic changes in the majority of USS cases (4 of 5), with minor glomerular pathology in the remaining case. In two of these four severe cases, more than half of the glomerular segmental sclerosis area was localized in the perihilar region. The average number of ADAMTS13-positive cells per glomerulus was significantly lower in USS cases than controls (p < 0.05). Conversely, C4d staining was significantly more prevalent in the glomerular capillary walls of USS cases than controls (p < 0.05), while C5b-9 staining did not differ significantly among groups. CONCLUSIONS: These findings suggest that the severity of glomerular injury in USS is associated with deficient ADAMTS13 expression and local complement activation, particularly in vascular regions with higher endothelial shear stress. We suggest that C4d immunostaining provides evidence for complement-mediated glomerular damage in USS.

von Willebrand factor and its cleaving protease ADAMTS13 balance in coronary artery vessels: Lessons learned from thrombotic thrombocytopenic purpura. A narrative review.

BACKGROUND: Deficiency of the von Willebrand factor-cleaving protease ADAMTS13 is central to the pathophysiology of thrombotic thrombocytopenic purpura (TTP), a microangiopathic syndrome that presents as an acute medical emergency. In this review we will explore the evidence of a two-way relationship between TTP and ACS. Moreover, we will review the evidence emerged from epidemiological studies of an inverse relationship between the plasma levels of ADAMTS13 and the risk of ACS. METHODS AND RESULTS: Pubmed, MEDLINE and EMBASE, CINHAL, COCHRANE and Google Scholar databases were searched from inception to January 2017. The search yielded 43 studies representing 23 unique patient cases, 5 case series, 5 cohort studies and 10 case-control studies. Most ACS cases developing in the setting of TTP resolved with standard treatment of the underlying microangiopathy, with only a few requiring coronary invasive management. Antiplatelet therapy was not usually prescribed and all of the currently used P2Y12 were felt to be a potential trigger for a TTP-like syndrome, although our review revealed that the occurrence of TTP in patients treated with new P2Y12 antagonists is rare. Most studies confirmed the inverse association among ADAMTS13 levels and ACS. CONCLUSIONS: The heart is a definite target organ in TTP. The clinical spectrum of its involvement is probably influenced by local factors that add on to the systemic deficiency characteristic of TTP. It follows that patients with TTP should be carefully monitored for ACS events, especially when multiple risk factors for coronary disease exist.

N-acetylcysteine in preclinical mouse and baboon models of thrombotic thrombocytopenic purpura.

Thrombotic thrombocytopenic purpura (TTP) is a microangiopathic disorder diagnosed by thrombocytopenia and hemolytic anemia, associated with a deficiency in von Willebrand factor (VWF)-cleaving protease ADAMTS13. Current treatment is based on plasma infusion for congenital TTP, or plasma exchange, often in combination with immunosuppressive agents, for acquired TTP. These treatment methods are not always effective; therefore, new treatment methods are highly necessary. N-acetylcysteine (NAC), an FDA-approved anti-mucolytic agent, is a possible new treatment strategy for TTP, as it was demonstrated to reduce disulfide bonds in VWF, thereby decreasing VWF multimers size and hence their prothrombotic potential. We investigated whether NAC, without concurrent plasma exchange and immunosuppressive therapy, is effective in preventing and resolving TTP signs, using well-established murine and baboon models for TTP. In mice, prophylactic administration of NAC was effective in preventing severe TTP signs. This in vivo finding was supported by in vitro data demonstrating the VWF multimer-reducing properties of NAC in solution. Nonetheless, in both mice and baboons, administration of NAC was not effective in resolving preexisting TTP signs; thrombocytopenia, hemolytic anemia, and organ damage could not be reversed, as thrombus resolution was not achieved. Failure to improve clinical outcome occurred even though a reduction in VWF multimers was observed, demonstrating that NAC was efficient in reducing disulfide bonds in circulating VWF multimers. In conclusion, prophylactic administration of NAC, without concurrent plasma exchange, was effective in preventing severe TTP signs in mice, but NAC was not effective in resolving preexistent acute TTP signs in mice and baboons.

ADAMTS13 and von Willebrand factor interactions.

PURPOSE OF REVIEW: ADAMTS13 is a zinc-containing metalloprotease that cleaves von Willebrand factor (VWF). Deficiency of plasma ADAMTS13 activity is accountable for a potentially fatal blood disorder thrombotic thrombocytopenic purpura (TTP). Understanding of ADAMTS13-VWF interaction is essential for developing novel treatments to this disorder. RECENT FINDINGS: Despite the proteolytic activity of ADAMTS13 being restricted to the metalloprotease domain, the ancillary proximal C-terminal domains including the disintegrin domain, first TSP-1 repeat, cysteine-rich region, and spacer domain are all required for cleavage of VWF and its analogs. Recent studies have added to our understandings of the role of the specific regions in the disintegrin domain, the cysteine-rich domain, and the spacer domain responsible for its interaction with VWF. Additionally, regulative functions of the distal portion of ADAMTS13 including the TSP-1 2-8 repeats and the CUB domains have been proposed. Finally, fine mapping of anti-ADAMTS13 antibody epitopes have provided further insight into the essential structural elements in ADAMTS13 for VWF binding and the mechanism of autoantibody-mediated TTP. SUMMARY: Significant progress has been made in our understandings of the structure-function relationship of ADAMTS13 in the past decade. To further investigate ADAMTS13-VWF interactions for medical applications, these interactions must be studied under physiological conditions in vivo.

Ultralarge von Willebrand factor-induced platelet clumping and activation of the alternative complement pathway in thrombotic thrombocytopenic purpura and the hemolytic-uremic syndromes.

The molecular linkage between ultralarge (UL) von Willebrand factor (VWF) multimers and the alternative complement pathway (AP) has recently been described. Endothelial cell (EC)-secreted and anchored ULVWF multimers (in long stringlike structures) function as both hyperadhesive sites that initiate platelet adhesion and aggregation and activating surfaces for the AP. In vitro, the active form of C3, C3b binds to the EC-anchored ULVWF multimeric strings and initiates the assembly on the strings of C3 convertase (C3bBb) and C5 convertase (C3bBbC3b). In vivo, activation of the AP via this mechanism proceeds all the way to generation of terminal complement complexes (C5b-9).

Evaluation of a chromogenic commercial assay using VWF-73 peptide for ADAMTS13 activity measurement.

INTRODUCTION: Thrombotic thrombocytopenic purpura (TTP) is a thrombotic microangiopathy (TMA), related to a severe functional deficiency of ADAMTS13 activity (<10% of normal). ADAMTS13 activity is thus crucial to confirm the clinical suspicion of TTP, to distinguish it from other TMAs, and to perform the follow-up of TTP patients. MATERIAL AND METHODS: We compared the performance of the commercial chromogenic assay Technozym ADAMTS13 Activity ELISA (chromogenic VWF73 substrate, Chr-VWF73, Technoclone, Vienna, Austria), to that of our in-house FRETS-VWF73 used as reference method. A large group of 247 subjects (30 healthy volunteers and 217 patients with miscellaneaous TMAs) was studied. RESULTS: The lower limit of detection of the Chr-VWF73 was 3%, which is well adapted to the clinically relevant threshold for TTP diagnosis (10%). Our results showed a reasonable agreement between FRETS-VWF73 and Chr-VWF73 assays to distinguish samples with an ADAMTS13 activity <10% from those with an ADAMTS13 activity >10%. However, Chr-VWF73 assay provided false negative results in ~12% of acute TTP patients. Inversely, the Chr-VWF73 assay globally underestimated ADAMTS13 activity in detectable values ranging from 11 to 100% (with a great variability compared to FRETS-VWF73), which may be a concern for the follow-up of TTP patients in remission. CONCLUSION: In-house assays developed and performed by expert laboratories remain the reference methods that should be used without limitation to control values provided by commercial assays when needed. Also, the development of an international reference preparation will be crucial to improve standardization.

Advances in our understanding of the pathogenesis of glomerular thrombotic microangiopathy.

Glomerular thrombotic microangiopathy is a hallmark feature of haemolytic uraemic syndrome, the leading cause of acute renal failure in childhood. This paper is a review of the different mechanistic pathways that lead to this histological picture in the kidney. It will focus on atypical HUS and complement dysregulation, but will also highlight some other recent advances in our understanding of this condition, including the potential role of the molecule vascular endothelial growth factor-A (VEGF-A).

Rituximab therapy to prevent relapse in chronic relapsing thrombotic thrombocytopenic purpura (TTP) in a child.

Our patient first developed thrombotic thrombocytopenic purpura (TTP) at age 10 years with an initial platelet count of 10,000/microL. She achieved remission with plasmapheresis (PE), but suffered 2 relapses in the next 2 years, each approximately 1 year from PE, with ADAMTS13 levels of <5%. Early in her third remission, with vincristine (weekly x 4 doses) and prednisone (for 2 weeks) her ADAMTS13 increased to 99% in 24 weeks, but decreased to <4% in the next 38 weeks. After 4 weekly doses of rituximab (375 mg/m(2)), her ADAMTS13 level reached 101% in 9 weeks and has remained consistently above 97% on bimonthly monitoring for more than a year. She remains in continuous clinical and hematologic remission with an ADAMTS13 level of 108% at 60 weeks from rituximab therapy and 124 weeks from her second relapse. This case report suggests that monitoring ADAMTS13 level at regular intervals in recurrent TTP may help us identify patients at risk for further relapse; and such a relapse may be prevented, or at least delayed with timely rituximab therapy, thus reducing morbidity from relapsed TTP and its treatment.

Thrombotic thrombocytopenia purpura (TTP) and other thrombotic microangiopathies.

Thrombotoic thrombocytopenic purpura (TTP) is a thrombotic microangiopathy characterised by systemic platelet aggregation, organ ischaemia, profound thrombocytopenia (with increased marrow megakaryocytes) and fragmentation of erythrocytes. Haemolytic-uraemic syndrome (HUS) is another type of thrombotic microangiopathy accompanied by renal dysfunction. In adults, a thrombotic microangiopathy that clinically more often resembles HUS than TTP may follow: bone marrow or solid organ transplantation and immunosuppression with cyclosporine or tacrolimus; total-body irradiation; mitomycin; gemcitabine; multiple chemotherapeutic agents; or antiangiogenic/antineoplastic substances. This article discusses the thrombotic microangiopathies that have provided the most extensive molecular insights to date into pathophysiology. These are familial and acquired forms of TTP associated with deficient plasma von Willebrand factor (VWF)-cleaving metalloprotease (ADAMTS-13) activity; acquired diarrhoea-associated HUS; the thrombotic microangiopathies associated with cyclosporine/tacrolimus or bevacizumab; and the preeclampsia-HELLP (haemolysis-elevated liver enzymes-low platelets) syndrome.

Berend Houwen Memorial Lecture: ISLH Las Vegas May 2009: the pathogenesis and management of thrombotic microangiopathies.

Thrombotic microangiopathies are a relatively rare group of congenital and inherited disorders caused by defects in processing the ultra large forms of von Willibrand factor which pathologically give rise to platelet rich microthrombi in the micro arterial circulation leading to end organ damage particularly in the brain, heart and kidneys. Identification of the ADAMTS 13 gene has led to the definition of congenital deficiency of its activity or failure of activity due to the development of an inhibitory IgG antibody. The idiopathic autoimmune form of the disease is the most common. There are various subgroups of acquired TTP associated with HIV infection, pregnancy, pancreatitis, associated with bone marrow transplantation, various disseminated malignancies and certain drugs, particularly Clopidogrel. Diagnostic assays are now becoming widely available to identify ADAMTS 13 activity and also acquired antibodies to the enzyme. Mainline treatment is associated with daily plasma exchange with associated other immunosuppressant treatments particularly steroids and recently the use of Rituximab, a monoclonal anti- CD20 antibody. Despite improvement in treatment modalities there is still significant mortality of 10-20%, particularly if there is a delay in initiating plasma exchange. Relapse also occurs in 20-50% of patients although this may be improved by Rituximab therapy.

Insights into von Willebrand factor proteolysis: clinical implications.

The proteolysis of von Willebrand factor (VWF) by the recently discovered metalloprotease ADAMTS13 (a disintegrin and metalloprotease with thrombospondin repeats), is a normal processing step in VWF biochemistry. Emerging data indicate that this step may be influenced by a variety of factors, some of which favour increased proteolysis and some of which compromise proteolysis. The former may predispose to bleeding, whilst the latter appears to be the underlying mechanism for thrombotic thrombocytopenic purpura (TTP). The new insights support the concept of "risk" in bleeding, particularly in the case of type 1 von Willebrand disease (VWD), in much the same way that risk is considered in venous thrombosis. This review presents relevant current knowledge of VWF proteolysis by ADAMTS13, and a novel model of how this may be implicated in type 1 VWD is proposed, based on events at the vessel wall at a time of haemostatic challenge.

Thrombotic thrombocytopenic purpura causing rapid unexpected death: value of CD61 immunohistochemical staining in diagnosis.

BACKGROUND: Thrombotic thrombocytopenic purpura (TTP) shares histologic features with disseminated intravascular coagulation (DIC) but is clinically distinct. TTP may result in myocardial hemorrhages and rapid death. We compared rapidly fatal TTP with heart involvement and DIC cases to determine if the differential diagnosis of TTP and DIC could be aided by immunohistochemical techniques. DESIGN: We examined 11 hearts from seven women and four men dying with TTP (aged 34+/-10 years) and 8 hearts from patients dying with DIC (five women, three men, aged 58+/-16 years). The diagnosis of TTP was established on histologic findings and identification of thrombocytopenia with schistocytes on premortem blood smear. Underlying conditions for TTP were recent diarrheal illness (3), autoimmune disease (3), sickle cell disease, HIV infection, cocaine abuse, and none known (2). Underlying conditions for DIC were disseminated carcinoma (4), multiorgan failure after open-heart surgery (2), pancreatitis (1), and placental abruption (1). Antibodies against platelet glycoprotein IIIa (CD61) and fibrin II were applied to formalin fixed tissue sections and detected by the avidin biotin techniques, and platelet and fibrin capillary thrombi were quantitated. RESULTS: Gross myocardial hemorrhages were present in 7/11 cases of TTP and 0 cases of DIC (P<.001). Capillary thrombi were present in all cases by routine histologic techniques but were often difficult to discern. Platelet thrombi were strongly highlighted by stains for CD61 and seen at a density of 8.0+/-3.1/mm(2) in TTP versus 0.5+/-0.4/mm(2) in DIC (P=.0001). In TTP, there were 12.1+/-5.9/mm(2) fibrin capillary thrombi and 4.8+/-5.8/mm(2) in DIC (P=.05). CONCLUSION: In the myocardium, rapidly fatal TTP is characterized by the diffuse presence of intracapillary platelet-rich thrombi, in contrast to DIC, which is characterized by predominantly fibrin thrombi. Immunohistochemical staining for CD61 and fibrin II is helpful in diagnosing TTP and distinguishing it from DIC.

Interplay between ADAMTS13 and von Willebrand factor in inherited and acquired thrombotic microangiopathies.

The presence of unusually large multimers of von Willebrand factor (VWF) is thought to be a major pathogenic factor for thrombotic thrombocytopenic purpura (TTP). ADAMTS13 is a protease that regulates the multimeric size and function of VWF by cleaving VWF. Hence, congenital or acquired deficiency of ADAMTS13 causes life-threatening illness of TTP. Mutations in the ADAMTS13 gene cause inherited TTP, and the development of autoantibodies that inhibit ADAMTS13 activity frequently are associated with acquired TTP. ADAMTS13 consists of 1,427 amino acid residues and is composed of multiple structural and functional domains, containing a signal peptide, a propeptide, a reprolysin-like metalloprotease domain, a disintegrin-like domain, a thrombospondin type-1 (Tsp1) motif, a cysteine-rich domain, a spacer domain, seven additional Tsp1 repeats, and two CUB domains. In particular, the cysteine-rich/spacer domains are essential for VWF cleavage and are the principal epitopes recognized by autoantibodies in patients with acquired TTP. Therefore, it is likely that these domains are involved in the recognition and binding of ADAMTS13 to VWF. ADAMTS13 circulates in the blood in an active state, and efficiently cleaves unfold form of VWF induced under shear stress caused by blood flow, preventing the accumulation of pathogenic unusually large VWF multimers (ULVWF). Thus, ADAMTS13 helps maintain vascular homeostasis by preventing the excess thrombus formation.

Effect of plasma exchange on plasma ADAMTS13 metalloprotease activity, inhibitor level, and clinical outcome in patients with idiopathic and nonidiopathic thrombotic thrombocytopenic purpura.

Therapeutic plasma exchange is an effective empiric treatment for thrombotic thrombocytopenic purpura (TTP), but how therapy affects the level of a disintegrin and metalloprotease with thrombospondin type 1 motif 13 (ADAMTS13) or inhibitor has not been reported in many patients. We prospectively analyzed ADAMTS13 activity and inhibitor levels in 37 adults with TTP. ADAMTS13 level at presentation was lower than 5% in 16 of 20 patients with idiopathic TTP and in none of 17 patients with TTP associated with hematopoietic stem cell transplantation, cancer, drugs, or pregnancy (P <.00001). Seven of the 16 patients with ADAMTS13 activity lower than 5% ( approximately 44%) had inhibitors. For 8 patients followed serially with ADAMTS13 activity lower than 5% but no inhibitor at presentation, plasma exchange led to complete clinical remission and a rise in ADAMTS13 level. In contrast, 4 patients with low ADAMTS13 activity but high-titer inhibitor (> 5 units/mL) had neither a rise in ADAMTS13 activity nor a reduction in the inhibitor titer: 3 had recurrent disease and 1 died. Among 17 patients with AD-AMTS13 activity at presentation higher than 25%, 10 died. Mortality rate for idiopathic TTP was 15%, whereas mortality for nonidiopathic TTP was 59% (P <.02). We conclude that assays of ADAMTS13 activity and inhibitors in addition to the clinical categories (idiopathic TTP and nonidiopathic TTP) are predictive of outcome and may be useful to tailor patient treatment.

Role of transforming growth factor beta1 in microvascular endothelial cell apoptosis associated with thrombotic thrombocytopenic purpura and hemolytic-uremic syndrome.

Primary human microvascular endothelial cells (MVEC) of restricted lineage undergo apoptosis when exposed to plasma from patients with thrombotic thrombocytopenic purpura (TTP) and sporadic hemolytic-uremic syndrome (HUS). This reflects the pathology and tissue distribution of lesions in vivo. As extracellular matrix (ECM) is critical to MVEC survival, and cytokines which regulate ECM, such as transforming growth factor (TGF)-beta1, have been reported anecdotally to be altered in TTP/HUS, we examined the role of TGF-beta1 and two ECM proteins, fibronectin and thrombospondin (TSP), in these disorders. Levels of active TGF-beta1 were elevated in acute but not convalescent phases of TTP/sporadic HUS, as well as TTP associated with human immunodeficiency virus infection and use of the anti-platelet drug ticlopidine. MVEC from tissues susceptible to TTP-mediated apoptosis showed little active TGF-beta1 production when exposed to TTP plasmas. In contrast, pulmonary MVEC and large-vessel EC, which are resistant to TTP-linked pathology, showed marked induction of TGF-beta1 following TTP plasma exposure. Exogenous TGF-beta1 suppressed TTP plasma-mediated apoptosis in susceptible MVEC in association with blockade of cell entry into S phase. Soluble TSP, devoid of detectable bound TGF-beta1, had a similar effect, which paralleled its ability to induce TGF-beta1 production in MVEC. In vivo, TSP deposition was diminished markedly in involved tissues of TTP patients. These data highlight the role of TGF-beta1 and ECM in TTP and suggest that differential production of TGF-beta1 by MVEC may play a role in their sensitivity or resistance to TTP/sporadic HUS-mediated apoptosis in vitro and in vivo.

Renal involvement of thrombotic thrombocytopenic purpura: special reference to the glomeruloid structures.

We report the case of a 9-year-old girl with biopsy-proven renal thrombotic microangiopathy in thrombotic thrombocytopenic purpura (TTP), with particular reference to the glomeruloid structures. The renal biopsy sample from this TTP patient revealed platelet thrombus deposition, a glomeruloid structure and aneurysm with relative sparing of the glomeruli. The glomeruloid structure displayed a proliferation of mainly capillary-sized channels lined by Factor VIII-related, antigen-positive plump endothelial cells embedded in the edematous connective tissue. These glomeruloid vessels communicated with the aneurysmal segment at the end portion of the arteriolar branch. We believe that the glomeruloid structures in TTP represent not merely organization or recanalization of thrombus but rather active angiogenesis through aneurysmal dilation in the arteriolized vessel, probably initiated by platelet agglutination.

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.

Increased von Willebrand factor binding to platelets in single episode and recurrent types of thrombotic thrombocytopenic purpura.

Extensive microvascular platelet aggregation is characteristic of thrombotic thrombocytopenic purpura (TTP). Previous studies have indicated that abnormalities of von Willebrand factor (vWf) are often present in TTP patient plasma. There has not been previously any direct evidence linking these abnormalities to the process of intravascular platelet aggregation in TTP. We used flow cytometry to analyze the binding of vWf to single platelets, and the presence of platelet aggregates, in the blood of 4 children with chronic relapsing (CR) TTP and 5 adults with single episode or recurrent TTP. vWf on the single platelets of CRTTP patients at all time points studied was significantly increased compared to controls, and was increased further as platelet counts decreased to levels below 40,000/microl. The single episode and recurrent adult TTP patients had platelet aggregates in the blood, as well as increased vWf on single platelets, before therapy commenced and thereafter until recovery was in process. In the one unresponsive single episode TTP patient, vWf on single platelets remained elevated, and platelet aggregates persisted, until her death. The platelet alpha-granular protein, P-selectin, was not increased on the single platelets of most TTP blood samples, suggesting that it is vWf from plasma (rather than from alpha-granules) that attaches to platelet surfaces in association with platelet aggregation. These results suggest that vWf-platelet interactions are involved in the platelet clumping process that characterizes TTP.