Thromboxane-dependent platelet activation in vivo precedes arterial thrombosis in thrombocythaemia: a rationale for the use of low-dose aspirin as an antithrombotic agent

Evaluation of platelet function in essential thrombocythemia under different analytical conditions

Background. Studies of platelet aggregation (PA) in essential thrombocythemia (ET) reported contrasting results, likely due to differences in analytical conditions.Objective. We investigated platelet aggregation using different techniques and analytical conditions.Patients and Methods. PA was studied by light-transmission aggregometry (LTA) in platelet-rich plasma (PRP) and impedance aggregometry in PRP and whole blood (WB). ADP, collagen, thrombin receptor activating peptide (TRAP-14) and adrenaline were used as agonists. Since ET patients (n = 41) were on treatment with aspirin (100 mg/d), healthy controls (n = 29) were given aspirin (100 mg/d) for 5 days before testing: therefore, thromboxane A₂-independent PA was tested in all subjects. Blood samples were collected in citrate (C) [low Ca²⁺] or lepirudin (L) [physiological Ca²⁺]; platelet count was adjusted to 250 x 10⁹/L in a set of C-PRP (adjusted C-PRP) and left unmodified in the other samples.Results. Results of PA in 17 ET patients who were poor responders to aspirin (high serum thromboxane B2 levels) were not included in the analysis. With LTA, PA in ET was lower than in controls in adjusted C-PRP and normal in native C-PRP and L-PRP. With impedance aggregometry, PA in L-PRP and L-WB tended to be higher in ET than in controls. Platelet serotonin and ADP contents were reduced in ET. The percentages of circulating platelets expressing P-selectin and platelet-leukocyte hetero-aggregates were higher in ET.Conclusions. Analytical conditions dramatically affect in vitro PA of ET patients, which appears defective under the least physiological conditions and normal/supranormal under conditions that are closer to the physiological.

Aspirin cures erythromelalgia and cerebrovascular disturbances in JAK2-thrombocythemia through platelet-cycloxygenase inhibition

Hypersensitive (sticky) platelets in JAK2-mutated essential thrombocythemia (ET) and polycythemia vera (PV) with thrombocythemia spontaneously activate at high shear in arterioles, secrete their inflammatory prostaglandin endoperoxides and induce platelet-mediated arteriolar fibromuscular intimal proliferation. Constitutively activated JAK2 mutated hypersensitive (sticky) platelets spontaneously aggregate at high shear in the endarteriolar circulation as the cause of aspirin responsive erythromelalgia and platelet arterial thrombophilia in JAK2-mutated thrombocythemia patients. Increased production of prostglandin endoperoxides E2 and thromboxane A2 released by activated sticky platelets in arterioles account for redness warmth and swelling of erythromelalgia and platelet derived growth factor can readily explain the arteriolar fibromuscular intimal proliferation. Von Willebrand factor (VWF) platelet rich occlusive thrombi in arterioles are the underlying pathobiology of erythromelalgic acrocyanosis, migraine-like transient cerebral attacks (MIAs), acute coronary syndromes and abdominal microvscular ischemic events. Irreversible platelet cyco-oxygenase inhibition by aspirin cures the erythromelalgia, MIAs and microvascular events, corrects shortened platelet survival to normal, and returns increased plasma levels of beta-TG, platelet factor 4, thrombomoduline and urinary thromboxane B2 excretion to normal in symptomatic JAK2-thrombocythemia patients. In vivo activation of sticky platelets and VWF-platelet aggregates account for endothelial cell activation to secrete thrombomoduline and sVCAM followed by occlusion of arterioles by VWF-rich platelet thrombi in patients with erythromelalgic thrombotic thrombocythemia (ETT) in ET and PV patients. ETT is complicated by spontaneous hemorrhagic thrombocythemia (HT) or paradoxical ETT/HT due to acquired von Willebrand disease type 2A at platelet counts above 1000 × 10⁹/L and disappears by cytoreduction of platelets to normal (< 400 × 10⁹/L).

Chronic Myeloid Leukemia: A Case of Extreme Thrombocytosis Causing Syncope and Myocardial Infarction

Chronic myeloid leukemia (CML), a hematologic malignancy characterized by unregulated growth of myelogenous leukocytes, typically presents with symptoms of fatigue, anorexia, and splenomegaly. Laboratory studies often reveal a significant leukocytosis with neutrophilia. A moderate thrombocytosis may be present, but is not usually problematic. The following case discusses a patient who presented with syncope, a convulsive episode, and non ST-segment myocardial infarction secondary to symptomatic thrombocytosis of 2.5 million cells/microL. She was treated with plateletpheresis and subsequently experienced resolution of symptoms. Ultimately, a diagnosis of CML with an atypical presentation of the disease was identified in this patient.

Guidelines for the management of myeloproliferative neoplasms

Polycythemia vera, essential thrombocythemia, and primary myelofibrosis are collectively known as 'Philadelphia-negative classical myeloproliferative neoplasms (MPNs).' The discovery of new genetic aberrations such as Janus kinase 2 (JAK2) have enhanced our understanding of the pathophysiology of MPNs. Currently, the JAK2 mutation is not only a standard criterion for diagnosis but is also a new target for drug development. The JAK1/2 inhibitor, ruxolitinib, was the first JAK inhibitor approved for patients with intermediate- to high-risk myelofibrosis and its effects in improving symptoms and survival benefits were demonstrated by randomized controlled trials. In 2011, the Korean Society of Hematology MPN Working Party devised diagnostic and therapeutic guidelines for Korean MPN patients. Subsequently, other genetic mutations have been discovered and many kinds of new drugs are now under clinical investigation. In view of recent developments, we have revised the guidelines for the diagnosis and management of MPN based on published evidence and the experiences of the expert panel. Here we describe the epidemiology, new genetic mutations, and novel therapeutic options as well as diagnostic criteria and standard treatment strategies for MPN patients in Korea.

Aspirin-responsive, migraine-like transient cerebral and ocular ischemic attacks and erythromelalgia in JAK2-positive essential thrombocythemia and polycythemia vera

Migraine-like cerebral transient ischemic attacks (MIAs) and ocular ischemic manifestations were the main presenting features in 10 JAK2(V617F)-positive patients studied, with essential thrombocythemia (ET) in 6 and polycythemia vera (PV) in 4. Symptoms varied and included cerebral ischemic attacks, mental concentration disturbances followed by throbbing headaches, nausea, vomiting, syncope or even seizures. MIAs were frequently preceded or followed by ocular ischemic events of blurred vision, scotomas, transient flashing of the eyes, and sudden transient partial blindness preceded or followed erythromelalgia in the toes or fingers. The time lapse between the first symptoms of aspirin-responsive MIAs and the diagnosis of ET in 5 patients ranged from 4 to 12 years. At the time of erythromelalgia and MIAs, shortened platelet survival, an increase in the levels of the platelet activation markers β-thromboglobulin and platelet factor 4 and also in urinary thromboxane B2 were clearly indicative of the spontaneous in vivo platelet activation of constitutively JAK2(V617F)-activated thrombocythemic platelets. Aspirin relieves the peripheral, cerebral and ocular ischemic disturbances by irreversible inhibition of platelet cyclo-oxygenase (COX-1) activity and aggregation ex vivo. Vitamin K antagonist, dipyridamole, ticlopidine, sulfinpyrazone and sodium salicylate have no effect on platelet COX-1 activity and are ineffective in the treatment of thrombocythemia-specific manifestations of erythromelalgia and atypical MIAs. If not treated with aspirin, ET and PV patients are at a high risk of major arterial thrombosis including stroke, myocardial infarction and digital gangrene.

Aspirin responsive platelet thrombophilia in essential thrombocythemia and polycythemia vera

Essential thrombocythemia (ET) and polycythemia vera (PV) frequently present with erythromelalgia and acrocyanotic complications, migraine-like microvascular cerebral and ocular transient ischemic attacks (MIAs) and/or acute coronary disease. The spectrum of MIAs in ET range from poorly localized symptoms of transient unsteadiness, dysarthria and scintillating scotoma to focal symptoms of transient monocular blindness, transient mono- or hemiparesis or both. The attacks all have a sudden onset, occur sequentially rather than simultaneously, last for a few seconds to several minutes and are usually associated with a dull, pulsatile or migraine-like headache. Increased hematocrit and blood viscosity in PV patients aggravate the microvascular ischemic syndrome of thrombocythemia to major arterial and venous thrombotic complications. Phlebotomy to correct hematocrit to normal in PV significantly reduces major arterial and venous thrombotic complications, but fails to prevent the platelet-mediated erythromelalgia and MIAs. Complete long-term relief of the erythromelalgic microvascular disturbances, MIAs and major thrombosis in ET and PV patients can be obtained with low dose aspirin and platelet reduction to normal, but not with anticoagulation. Skin punch biopsies from the erythromelalgic area show fibromuscular intimal proliferation of arterioles complicated by occlusive platelet-rich thrombi leading to acrocyanotic ischemia. Symptomatic ET patients with erythromelalgic microvascular disturbances have shortened platelet survival, increased platelet activation markers β-thromboglobulin (β-TG), platelet factor 4 (PF4) and thrombomoduline (TM), increased urinary thromboxane B2 (TXB2) excretion, and no activation of the coagulation markers thrombin fragments F1+2 and fibrin degradation products. Inhibition of platelet cyclooxygenase (COX1) by aspirin is followed by the disappearance and no recurrence of microvascular disturbances, increase in platelet number, correction of the shortened platelet survival times to normal, and reduction of increased plasma levels of β-TG, PF4, TM and urinary TXB2 excretion to normal. These results indicate that platelet-mediated fibromuscular intimal proliferation and platelet-rich thrombi in the peripheral, cerebral and coronary end-arterial microvasculature are responsible for the erythromelalgic ischemic complications, MIAs and splanchnic vein thrombosis. Baseline platelet P-selectin levels and arachidonic acid induced COX1 mediated platelet activation showed a highly significant increase of platelet P-selectin expression (not seen in ADP and collagen stimulated platelets), which was significantly higher in JAK2^V617F mutated compared to JAK2 wild type ET.

Thrombocytosis: diagnostic evaluation, thrombotic risk stratification, and risk-based management strategies

Thrombocytosis is a commonly encountered clinical scenario, with a large proportion of cases discovered incidentally. The differential diagnosis for thrombocytosis is broad and the diagnostic process can be challenging. Thrombocytosis can be spurious, attributed to a reactive process or due to clonal disorder. This distinction is important as it carries implications for evaluation, prognosis, and treatment. Clonal thrombocytosis associated with the myeloproliferative neoplasms, especially essential thrombocythemia and polycythemia vera, carries a unique prognostic profile, with a markedly increased risk of thrombosis. This risk is the driving factor behind treatment strategies in these disorders. Clinical trials utilizing targeted therapies in thrombocytosis are ongoing with new therapeutic targets waiting to be explored. This paper will outline the mechanisms underlying thrombocytosis, the diagnostic evaluation of thrombocytosis, complications of thrombocytosis with a special focus on thrombotic risk as well as treatment options for clonal processes leading to thrombocytosis, including essential thrombocythemia and polycythemia vera.

JAK2(V617F) positive early stage myeloproliferative disease (essential thrombocythemia) as the cause of portal vein thrombosis in two middle-aged women: therapeutic implications in view of the literature

The present study describes portal vein thrombosis (PVT) in two women as the first and single presenting symptom of latent or masked myeloproliferative disease (MPD). Essential thrombocythemia (ET) was suspected by a sustained increase in platelet count (>400 x 10(9)/l) and slight splenomegaly on echogram. ET could be diagnosed by the presence of large platelet in peripheral blood smear, an increase in clustered large megakaryocytes in bone marrow smear and the presence of the JAK2(V617F) mutation. A subsequent biopsy specimen was consistent with the diagnosis of true ET. In patients with a first episode of splanchnic vein thrombosis (SVT), analysis of any venous thrombophilic risk factors as well as a JAK2(V617F) mutation status indicative for MPD is warranted. Administration of heparin followed by oral anticoagulation with vitamin K antagonists is the treatment of choice in patients with SVT. Anticoagulation therapy combined with low-dose aspirin and proper treatment of the MPD is recommended in patients with SVT associated with the JAK2(V617F) mutation.

The treatment of polycythaemia vera: an update in the JAK2 era

The clinical course of polycythaemia vera is marked by a high incidence of thrombotic complications, which represent the main cause of morbidity and mortality. Major predictors of vascular events are increasing age and previous thrombosis. Myelosuppressive drugs can reduce the rate of thrombosis, but there is concern that their use raises the risk of transformation into acute leukaemia. To tackle this dilemma, a risk-oriented management strategy is recommended. Low-risk patients should be treated with phlebotomy and low-dose aspirin. Cytotoxic therapy is indicated in high-risk patients, with the drug of choice being hydroxyurea because its leukaemogenicity is low. The recent discovery of JAK2 V617F mutation in the vast majority of polycythaemia vera patients opens new avenues for the treatment of this disease. Novel therapeutic options theoretically devoid of leukaemic risk, such as alpha-interferon and imatinib, affect JAK2 expression in some patients. Nevertheless, these drugs require further clinical experience and, for the time being, should be reserved for selected cases.

Platelet-mediated erythromelalgic, cerebral, ocular and coronary microvascular ischemic and thrombotic manifestations in patients with essential thrombocythemia and polycythemia vera: a distinct aspirin-responsive and coumadin-resistant arterial thrombophilia

Microvascular circulation disturbances including erythromelalgia, its microvascular ischemic complications, and migraine-like atypical or typical transient ischemic cerebral, ocular, and coronary ischemic attacks are specific clinical manifestations in patients with essential thrombocythemia (ET), and polycythemia vera (PV) associated with thrombocythemia. Thrombocythemia (ET and PV) patients with microvascular disturbances have shortened platelet survival, increased beta-thromboglobulin (beta-tg), platelet factor 4 (PF4), and thrombomoduline (TM) levels, and increased urinary thromboxane B2 (TxB2) excretion indicating platelet-mediated processes in vivo. Inhibition of platelet cyclooxygenase (COX 1) by aspirin is followed by relief of microvascular disturbances, correction of shortened platelet survival, and return of plasma levels of beta-tg, PF4, TM levels and TxB2 excretion to normal. The transient ischemic attacks and thrombotic complications in thrombocythemia are very likely caused by hypersensitive platelets produced by spontaneously proliferating enlarged megakaryocytes in the bone marrow of ET and PV patients. In contrast to normal platelets in healthy individuals the circulating hypersensitive thrombocythemic platelets spontaneously activate and secrete their products, thus forming aggregates that transiently plug the microcirculation, or result in occlusive platelet thrombi in arterioles or small arteries. Clear evidence is presented that the microvascular transient ischemic and occlusive thrombotic complications in thrombocythemia patients are relieved by treatment with aspirin and by reduction of platelet counts to normal (<400 x 109/l), but not by coumadin. In patients with thrombocythemia associated with PV, increased hematocrit and whole blood viscosity aggravate the platelet-mediated microvascular ischemic and thrombotic syndrome of thrombocythemia to major arterial and venous thrombotic complications. Correction of hematocrit and blood viscosity by phlebotomy significantly reduces the major arterial and venous thrombotic complications, but fails to prevent the platelet-mediated microvascular circulation disturbances in PV patients because thrombocythemia persists. Complete relief and prevention of microvascular and major thrombosis in PV patients are obtained by treatment with low-dose aspirin on top of phlebotomy or by treatment with the platelet lowering agents, anagrelide, interferon or hydroxyurea.

Platelet-mediated thrombotic complications in patients with ET: Reversal by aspirin, platelet reduction, and not by coumadin

The broad spectrum of aspirin-sensitive erythromelalgia, its microvascular ischemic complications, migraine-like atypical or typical transient ischemic attacks (cerebral and ocular) as well as acute coronary syndromes in thrombocythemia vera (essential thrombocythemia and thrombocythemia associated with polycythemia vera in maintained remission by phlebotomy) is caused by platelet cyclo-oxygenase-mediated arteriolar inflammation, fibromuscular intimal proliferation without and with occlusive thrombosis by platelet-rich thrombi in the end-arterial microvasculature of the peripheral, cerebral, ocular and coronary circulation. These microvascular ischemic and thrombotic complications does not respond to Coumadin, but are immediately relieved by a loading dose of 500 mg aspirin, and does not recur when the patient is maintained on low dose aspirin (50 mg per day) or after reduction of platelet counts to normal (<400.000/microl).

Treatment of symptomatic patients with essential thrombocythemia: effectiveness of anagrelide

We prospectively evaluated the effect of anagrelide (ANA) on platelets, PF4, F1+2, PAP, PAI-1, and TFPI and erythromelalgia in patients with essential thrombocythemia (ET) receiving anti-aggregants both pre- and post-ANA. At first, we observed a successful reduction of platelets, which was associated with normalization of platelet coagulant and endothelial function and disappearance of erythromelalgia. Secondly, we found a correlation between PF4 and TFPI and between TFPI and thrombosis, suggesting that erythromelalgia may be caused by platelet-mediated endothelial activation. These data may indicate that ANA may be efficacy in the treatment of symptomatic patients with ET.

Primary and secondary thrombocytosis in childhood

This review summarizes current data on the pathomechanisms and clinical aspects of primary and secondary thrombocytosis in childhood. Primary thrombocytosis is extremely rare in childhood, mostly diagnosed at the beginning of the second decade of life. As in adults, the criteria of the Polycythemia Vera Group are appropriate to diagnose primary thrombocytosis. The pathomechansims of non-familial forms are complex and include spontaneous formation of megakaryopoietic progenitors and increased sensitivity to thrombopoietin (Tpo). Familial forms can be caused by mutations in Tpo or Tpo receptor (c-mpl) genes. These mutations result in overexpression of Tpo, sustained intracellular signalling or disturbed regulation of circulating Tpo. Treatment of primary thrombocytosis is not recommended if platelet counts are <1500/nl and bleeding or thrombosis did not occur in patient's history. In severe cases, decision on treatment should weigh potential risks of treatment options (hydroxyurea, anagrelide) against expected benefits for preventing thrombosis or haemorrhage. Secondary thrombocytosis is frequent in children, in particular in the first decade of life. Hepatic Tpo production is stimulated in acute response reaction to a variety of disorders. Thrombosis prophylaxis is not required, even at platelet counts >1000/nl, except for cases with additional prothrombotic risk factors.

Pathophysiology and treatment of platelet-mediated microvascular disturbances, major thrombosis and bleeding complications in essential thrombocythaemia and polycythaemia vera

Essential thrombocythaemia (ET) is associated with a broad spectrum of microvascular circulation disturbances including erythromelalgia and its ischaemic complications, episodic neurological symptoms of atypical and typical transient ischaemic attacks (TIAs), transient ocular ischaemic attacks, acute coronary syndromes, and superficial 'thrombophlebitis'. The microvascular circulation disturbances are caused by spontaneous activation and aggregation of hypersensitive thrombocythaemic platelets at high shear stress in the endarterial microcirculation involving the peripheral, cerebral and coronary circulation. As this microvascular syndrome is a pathognomonic feature of essential thrombocythaemia and of thrombocythaemia associated with polycythaemia vera (PV) in complete remission with normal haematocrit, we have labelled these two variants of thrombocythaemia as thrombocythaemia vera. The arterial thrombophilia of microvascular circulation disturbances in thrombocythaemia vera already occur at platelet counts in excess of 400 x 10(9)/l. Complete relief of microvascular circulation disturbances in thrombocythaemia vera is obtained with the platelet cyclooxygenase inhibitor aspirin 50-100 mg/day, but not with dipyridamole, ticlopidine, coumarin or heparin. Haemorrhagic thrombocythaemia (HT) is a clinical syndrome of recurrent spontaneous mucocutaneous and secondary haemorrhages associated with extremely high platelet counts far in excess of 1000 x 10(9)/l. The paradoxical occurrence of microvascular circulation disturbances and mucocutaneous bleeding is usually seen at platelet counts between 1000 and 2000 x 10(9)/l. At increasing platelet counts from below 1000 to in excess of 2000 x 10(9)/l, the arterial thrombophilia of thrombocythaemia vera changes into a spontaneous bleeding tendency of HT as a consequence of platelet-mediated increased proteolysis of the large von Willebrand factor multimers leading to a type 2 acquired von Willebrand syndrome. As PV is usually associated with thrombocythaemia, the vascular complications in PV patients are microvascular circulation disturbances typical of thrombocythaemia. On top of this, major arterial and venous thrombotic events and haemorrhages are related to increased haematocrit, red cell mass and its concomitant increased blood viscosity. Correction of increased blood viscosity and haematocrit to normal values (0.40-0.44) by bloodletting alone will significantly reduce the risk of major thrombotic complications, but does not prevent the microvascular circulation disturbances because thrombocythaemia persists. The microvascular syndrome associated with thrombocythaemia in PV patients in remission after bloodletting is best controlled by low-dose aspirin (50-100 mg/day) or by reduction of platelet count to normal (< 350 x 10(9)/l).

Thrombocythemia and hemoperitoneum after transvaginal oocyte retrieval for in vitro fertilization

OBJECTIVE

To present the first report of massive hemoperitoneum in a case of essential thrombocythemia after transvaginal oocyte retrieval for IVF and review the relevant literature related to the management of patients with this condition.

DESIGN

Case report.

SETTING

Assisted conception unit of a tertiary care university hospital in the United Kingdom.

PATIENT(S)

A 37-year-old woman with essential thrombocythemia who developed massive intra-abdominal bleeding after transvaginal oocyte retrieval for IVF.

INTERVENTION(S)

Emergency laparotomy and right salpingoophorectomy.

RESULT(S)

Resuscitation of the patient.

MAIN OUTCOME MEASURE(S)

Overall management of the patient is discussed.

CONCLUSION(S)

The management of patients with essential thrombocythemia at the childbearing period poses a difficult problem. Fertility may be reduced, and an adverse outcome of pregnancy due to thrombotic or bleeding complications is a matter of concern. A multidisciplinary approach with close and early cooperation with the hematologists before initiation of IVF therapy for patients with essential thrombocythemia is essential. Efforts should be made to reduce the platelet count and assess the platelet function before embarking on IVF, keeping in mind the double jeopardy from bleeding and thrombosis in these cases.

Markers of endothelial and in vivo platelet activation in patients with essential thrombocythemia and polycythemia vera

We investigated endothelial and in vivo platelet activation in a cohort of 52 patients with essential thrombocythemia (ET) and polycythemia vera (PV) before and after cytoreductive treatment, 22 healthy controls, and 17 patients with acute cerebrovascular ischemia (ACVI) and normal platelet counts. We measured platelet expression of CD62P and CD63 antigens and levels of soluble vascular cell adhesion molecule 1 (sVCAM-1). We found increased in vivo platelet activation in all patients with ET and PV, both before and after cytoreductive treatment, compared with controls. In patients with arterial thrombosis, platelet expression of CD62P, and in patients with erythromelalgia, expression of both markers was higher compared with expression in patients without thrombotic complications. In patients with ET and PV before and after treatment, sVCAM-1 expression was increased compared with expression in controls but also compared with expression in patients with ACVI and normal platelet counts. In patients with arterial thrombosis and erythromelalgia, in vivo platelet activation correlated with the level of sVCAM-1. Our findings indicated that in vivo platelet activation reflects intrinsic platelet defects in patients with ET and PV, persists after cytoreductive treatment, and results in endothelial damage, probably through release of angiogenic factors and/or activation of white blood cells.

Platelet-mediated microvascular inflammation and thrombosis in thrombocythemia vera: a distinct aspirin-responsive arterial thrombophilia, which transforms into a bleeding diathesis at increasing platelet counts

Erythromelalgia is the main, pathognomonic and presenting symptom in patients with essential thrombocythemia and thrombocythemia associated with polycythemia vera. Complete relief from erythromelalgic and acrocyanotic pain is obtained with the cyclooxygenase inhibitors aspirin and indomethacin, but not with sodiumsalicylate, dipyridamol, sulfinpyrozone and ticlopedine. Thus, cyclooxygenase metabolites are necessary for erythromelalgia to develop. Local platelet consumption in erythromelalgic areas became evident by the demonstration of arteriolar fibromuscular intimal proliferation and occlusions by platelet-rich thrombi in skin biopsies, by the findings of shortened platelet survival times, significant higher levels of platelet activation markers beta-thromboglobulin, thrombomoduline and increased urinary thromboxane B2 excretion in thrombocythemia patients suffering from erythromelalgia. Aspirin treatment of erythromelalgia in thrombocythemia patients resulted in the disappearance of the erythromelalgic, thrombotic signs and symptoms, correction of the shortened platelet survival times, and a significant reduction of the increased levels of beta-TG, PF4, TM and urinary TxB2 excretion to normal. Erythromelalgia is frequently preceded or followed by atypical transient neurologic, ocular or coronary ischemic symptoms, which specifically respond to low-dose aspirin or reduction of platelet counts to normal. The broad spectrum of acropareshesias, erythromelalgia and acrocyanotic ischemia together with the episodic and transient atypical TIAs and ocular or coronary ischemic symptoms are caused by spontaneous activation and aggregation of hypersensitive platelets in the end-arterial microvasculature involving the peripheral, cerebral and coronary circulation of thrombocythemia patients. These microvascular circulation ischemic disturbances in thrombocythemia vera already occur at platelet counts in excess of 400 x 10(9) l(-1). Low-dose aspirin is highly effective and safe in the cure and prevention of thrombotic and ischemic events and does not elicit bleedings at platelet counts below 1000 x 10(9) l(-1). Spontaneous hemorrhages usually occur at very high platelet counts far in excess of 1000 x 10(9) l(-1) (HT) due to an acquired von Willebrand factor deficiency at increasing platelet counts. At platelet counts between 1000 and 2000 x 10(9) l(-1), thrombosis and bleeding (ETT and HT) frequently occur in sequence or paradoxically and low-dose aspirin does prevent thrombotic complications but aggravates or may elicit bleeding symptoms. Reduction of the platelet count to below 1000 x 10(9) l(-1) by platelet lowering agents usually results in the disappearance of the bleeding tendency and improvement of the von Willebrand syndrome, but the thrombotic tendency persists as long as platelet counts are above the upper limit of normal.

Polycythemia vera: a comprehensive review and clinical recommendations

More than a century has elapsed since the appearance of the modern descriptions of polycythemia vera (PV). During this time, much has been learned regarding disease pathogenesis and PV-associated molecular aberrations. New information has allowed amendments to traditional diagnostic criteria. Phlebotomy remains the cornerstone treatment of PV, whereas myelosuppressive agents may augment the benefit of using phlebotomy for thrombosis prevention in high-risk patients. Excessive aspirin use is contraindicated in PV, although the use of lower-dose aspirin has been shown to be safe and effective in alleviating microvascular symptoms including erythromelalgia and headaches. Recent studies have shown the utility of selective serotonin receptor antagonists for treating PV-associated pruritus. Nevertheless, many questions remain unanswered. What is the specific genetic mutation or altered molecular pathway that is causally related to the disease? In the absence of a specific molecular marker, how is a working diagnosis of PV made? What evidence supports current practice in the management of PV? This article summarizes both old and new information on PV; proposes a modern diagnostic algorithm to formulate a working diagnosis; and provides recommendations for patient management, relying whenever possible on an evidence-based approach.

Essential thrombocythemia (ET): moving from palliation to cure

Essential thrombocythemia (ET) is a clonal hematopoietic stem cell myeloproliferative disorder characterized by megakaryocytic hyperplasia and persistent thrombocytosis. The clinical presentation and evolution of ET are heterogeneous. This review highlights the current treatment options in the management of ET, including hydroxyurea, anagrelide and both regular and pegylated interferons. Anagrelide, while very effective at controlling counts and symptoms in most patients, may not consistently reduce the bone marrow megakaryocyte mass. Interferon is very effective and not associated with leukemogenesis, but has not been proven to restore polyclonal hematopoiesis and has significant dose-related adverse events. Pegylated interferon represents a significant improvement over the unmodified interferon preparations. Novel therapeutic options directed towards eradication of the malignant ET clone are required.

Polycythemia vera--a case report and discussion on pathogenic mechanisms of increased thrombosis

Polycythemia vera is a myeloproliferative disorder characterized by increased red cell mass and frequently complicated by venous and arterial thrombosis. The mechanism underlying the increased incidence of thrombotic events remains illusive. Presented in this report are a case of a 77-year-old man diagnosed with polycythemia vera and a review of the current literature on the mechanisms underlying the increased incidence of thrombotic events in polycythemia vera.

Frequent occurrence of anticardiolipin antibodies, Factor V Leiden mutation, and perturbed endothelial function in chronic myeloproliferative disorders

Chronic myeloproliferative disorders (MPD) are characterized by a high incidence of thrombohaemorrhagic complications, possibly related to platelet abnormalities and disturbances of the coagulation system. In an attempt to define abnormalities in coagulation and fibrinolysis, we investigated risk markers for venous thromboembolism, fibrinolytic, and haemostatic system activation markers and antiphospholipid antibodies in blood samples from 50 MPD patients and 30 controls. Compared with controls median levels of protein S free and protein C were significantly decreased in the patients (0.27 vs. 0.38 arbitrary units; P < 0.001 and 0.86 vs. 0.99 arbitrary units; P < 0.001, respectively), and activated partial thromboplastin time was significantly prolonged in patients (33 vs. 27 sec; P < 0.001). No differences were observed in levels of antithrombin, thrombin-antithrombin complex, and fibrin D-dimer. In patients the median value of thrombomodulin was significantly increased indicating perturbed endothelial function. Anticardiolipin antibodies of IgM subtype (median 38 U/mL, 33-99) were detected in 11 patients (22%) and only in one control (3%) (P < 0.021; patients vs. controls). Seven patients were heterozygous for the Factor V Leiden, one patient was heterozygous for the prothrombin G20210A mutation, and one patient was homozygous for the Factor V Leiden mutation. Among controls, two were heterozygous for the Factor V Leiden mutation. Comparing the allele frequency of the Factor V Leiden mutation in patients with MPD and the background population disclosed a significantly increased allele prevalence of the Factor V Leiden mutation in the patients (9% vs. 3.4%; P = 0.003). Alterations in the level of anticoagulant proteins, disturbances of endothelial cell function, and the presence of cardiolipin antibodies and Factor V Leiden mutation may increase the cumulative thrombotic risk in MPD besides the risk imposed by platelet activation.

A single institutional experience with 43 pregnancies in essential thrombocythemia

OBJECTIVES

We describe the periconception circumstances and outcome of 43 consecutive pregnancies in an unselected group of young women with essential thrombocythemia (ET).

PATIENTS AND METHODS

We retrospectively studied 74 consecutive cases of young women with ET seen at our institution, among whom 43 pregnancies occurred in 20 patients.

RESULTS

Of the 43 pregnancies, 22 (51%) were successful (21 term and 1 preterm live births) and 21 (49%) ended in miscarriages (1 ectopic pregnancy, 2 elective abortions, 16 first-trimester spontaneous abortions, 1 stillbirth at 22 wk, and 1 abruptio placentae at 33 wk). Management of ET at the time of conception included either no specific therapy (16 cases) or the use of aspirin alone (24 cases), a cytoreductive agent (2 cases), or heparin (1 case). There were no significant differences with respect to platelet count or the effect of treatment with aspirin, either at the time of conception or during the first trimester, among cases of successful pregnancies (22), all miscarriages (21), or first-trimester spontaneous abortions (16). The findings were similar when the analysis was restricted to only first-time pregnancies. In patients with multiple pregnancies, the outcome of a subsequent pregnancy was not predicted by the outcome of the first. In general, in successful cases the last two trimesters were mostly uneventful, with healthy offspring being reported in all cases.

CONCLUSIONS

Pregnant patients with ET have an increased risk of first-trimester abortion which is not predictable by preconception platelet count or aspirin therapy. In addition, our experience does not support the use of prophylactic platelet apheresis during delivery.

Medical management of a large aortic thrombus in a young woman with essential thrombocythemia

Aortic thrombus formation is rare in the patients with essential thrombocytosis (ET); therefore, no guidelines for its management have been established. Embolism from ET-associated large vessel thrombi is potentially lethal and has been managed surgically in a few reported cases. We describe herein a 45-year-old black woman with ET found to have a 3.5-cm, pedunculated intra-aortic thrombus at the thoracoabdominal junction. How to treat this potentially devastating aortic thrombus was a management dilemma. We believed, based on the patient's diagnosis of ET and the histology of similar thrombi in 1 reported series, that the aortic thrombus was a "white thrombus" consisting primarily of aggregated platelets with a minimal fibrin network and almost no entrapped erythrocytes. The patient was treated with aspirin, 325 mg daily, as a platelet antiaggregating agent and hydroxyurea, 1,500 mg daily, to reduce the platelet count to less than 450 x 10(9)/L. The thrombus resolved without severe thromboembolic events. To our knowledge, this is the first reported case of a large intra-aortic thrombosis associated with ET that has been successfully managed with medical therapy alone.

Acquired thrombophilic syndromes

As the biochemical mechanisms of hypercoagulable states are revealed, the syndromes of venous thromboembolism have been increasingly associated with specific aberrations. Most of these changes involve an increase in procoagulant potential, for example, by activation of the coagulation cascade, or by a defect or decrease in natural inhibitors of clotting. Similar abnormalities of the fibrinolytic pathways may contribute, as can loss of inhibitory mechanisms of endothelial cells, as well as changes in vascular anatomy and rheologic patterns of blood flow. All of these factors can directly influence thrombus formation and/or the physiologic response to the thrombus.(1)

Cisplatin triggers platelet activation

Clinical observations suggest that anticancer drugs could contribute to the thrombotic complications of malignancy in treated patients. Thrombotic microangiopathy, myocardial infarction, and cerebrovascular thrombotic events have been reported for cisplatin, a drug widely used in the treatment of many solid tumours. The aim of this study is to explore in vitro cisplatin effect on human platelet reactivity in order to define the potentially active role of platelets in the pathogenesis of cisplatin-induced thrombotic complications. Our results demonstrate that cisplatin increases human platelet reactivity (onset of platelet aggregation wave and thromboxane production) to non-aggregating concentrations of the agonists involving arachidonic acid metabolism. Direct or indirect activation of platelet phospholipase A(2) appears to be implicated. This finding contributes to a better understanding of the pathogenesis of thrombotic complications occurring during cisplatin-based chemotherapy.

Polycythaemia vera and essential thrombocythaemia in the elderly

Essential thrombocythaemia (ET) and polycythaemia vera (PV) both belong to the group of chronic myeloproliferative disorders which originate at the haematopoietic stem cell level with retention of their cellular differentiating capacity. The clinical course of both ET and PV is frequently complicated by potentially life-threatening thrombotic events and a variable rate of progression to myelofibrosis and leukaemic conversion (the latter in particular for PV). However, due to the relative paucity of randomised clinical trials in both ET and PV, a sound scientific basis for making therapeutic decisions is lacking. The management of patients with ET or PV should probably be addressed by categorising patient populations into groups with either a 'low risk' or 'high risk' for thrombosis after taking into account the risk factors for thrombosis (advanced age and/or previous thrombotic complications, and increased haematocrit). The goal of treatment in PV and ET is, however, not only to reduce the risk of thrombosis but also to reduce the risk of transformation into acute myeloid leukaemia or myelofibrosis. In this review we will discuss in detail the diagnosis, clinical manifestations and epidemiology, rationale for treatment, and the various treatment options for ET and PV with an emphasis on treatment efficacy and therapy-related leukaemic risk.

Increased platelet activation and abnormal membrane glycoprotein content and redistribution in myeloproliferative disorders

Chronic myeloproliferative disorders (MPDs) are characterized by a high incidence of thrombohaemorrhagic complications, possibly caused by platelet dysfunction. In an attempt to define platelet functional abnormalities, we assessed the expression of activation-dependent membrane proteins in unstimulated and agonist [ADP and thrombin receptor-activating peptide (TRAP)]-stimulated platelets using quantitative whole blood flow cytometry in samples from 50 MPD patients and 30 controls. The receptor densities of activation markers and glycoproteins (GPs) were quantified using standardized fluorescent beads. Compared with controls, the mean percentage of P-selectin-positive (15.3% vs. 7.2%; P < 0.001) and thrombospondin (TSP)-positive (6.6% vs. 3.7%; P = 0.003) platelets was increased in unstimulated platelets from patients. Patients having experienced a thrombotic event had a higher mean percentage of TSP-positive non-stimulated platelets than patients without a history of thrombosis (9.0% vs. 4.6%; P = 0.02) and a higher GPIV molecules of equivalent fluorochrome (MEF) value (33113 vs. 24471 MEF; P = 0.02). Mean MEF values of monoclonal antibodies (mAbs) against GPIb (34055 vs. 38945 MEF; P < 0.001) and GPIIb/IIIa (1416 vs. 1648 MEF; P < 0. 001) were significantly reduced among patients, whereas surface expression of GPIV was increased in patients (28273 vs. 16258 MEF; P < 0.001). In TRAP (10 micromol/l) stimulated whole blood, the MEF of P-selectin (9611 vs. 13293 MEF; P = 0.004) and CD63 (2385 vs. 5177 MEF; P < 0.001) and the ratio of PAC-1/GPIIb/IIIa MEF (0.98 vs. 2. 00; P < 0.001) was reduced in patients, indicating either a reduced granule GP content or an intrinsic cellular defect in receptor-mediated granule secretion and activation of the GPIIb/IIIa complex. Expressed as the relative change of MEF compared with unstimulated platelets, TRAP induced decrease of GPIb (7.8% vs. 45%; P < 0.001) and increase of GPIIb/IIIa (49.1% vs. 95.7%; P < 0.001) and GPIV expression (17.8% vs. 55.2%; P < 0.001) was attenuated in patients.

Diagnosis and treatment of polycythemia vera and possible future study designs of the PVSG

The present study describes clinicopathological criteria to distinguish the 5 sequential stages proposed by Wasserman et al in the natural history of newly diagnosed PV patients. The European Working Group on MPD (EWG.MPD) extended and modified the PVSG diagnostic criteria of PV by including bone marrow histopathology. From the results of prospective randomized studies in PV it became evident that new clinical trials in previously untreated PV patients should focus on comparing interferon-alpha, a non-leukemogenic approach, versus a potential leukemogenic myelosuppressive treatment modality. Hydroxyurea appears to be the least leukemogenic myelosuppressive agent in long-term prospective clinical PV-studies extending observation periods of more than 10 years. The rational for using IFN-alpha as a first-line treatment option in newly diagnosed PV-patient include its effectiveness to abate constitutional symptoms and to induce a complete remission thereby avoiding phlebotomy, iron deficiency, and macrocytosis associated with hydroxyurea. Moreover IFN-alpha may prevent or delay the development of postpolycythemic myelofibrosis if used early in the course of the disease. Clinicians will be reluctant to postpone the use of hydroxyurea in early stage PV as long as a conservative approach using phlebotomy aiming at a hematocrit below 0.45, plus low-dose aspirin for the control platelet function or anagrelide for the control platelet number is used to keep the patient healthy. Low-dose aspirin will prevent the microvascular thrombotic complications of thrombocythemia associated with PV in remission after phlebotomy, but lacks myelosuppressive activity. Control of megakaryocyte maturation and reduction of platelet production to normal (<400 x 10(9)/l) by relatively low doses of anagrelide will predict a significant reduction of vascular complications in the early stages of PV, may prevent progression to myelofibrosis during follow-up of PV and very probable will postpone the use of hydroxyurea treatment for controlling the platelet count in PV. Large scale randomized clinical trials in PV are proposed, which should aim not only for clinical and hematological response, safety, efficacy, but should also assess toxicity, the need for phlebotomy and whether the development of progressive disease such as splenomegaly, pruritus, myelofibrotic myeloid metaplasia, spent phase, myelodysplasia and acute leukemia can be delayed or prevented by IFN-alpha as compared to a conservative approach of phlebotomy plus low-dose aspirin or anagrelide followed by hydroxyurea when signs of myeloproliferative activity became evident.

Aspirin and platelet-lowering agents for the prevention of vascular complications in essential thrombocythemia

Low-risk essential thrombocythemia patients include patients aged 18 to < 80 years with no vascular risk factor or previous thrombosis, no associated disease, a normal life expectancy, and a platelet count between 400 and 1,000 x 10(9)/L up to 1,500 x 10(9)/L. Asymptomatic essential thrombocythemia patients may be at risk for microvascular circulation disturbances. The indication for low-dose aspirin in asymptomatic essential thrombocythemia patients is uncertain, therefore randomization for aspirin 50 mg versus placebo is recommended. Symptomatic essential thrombocythemia patients with erythromelalgia and its ischemic complications, atypical transient ischemic attacks, minor stroke, visual disturbances and "superficial thrombophlebitis" in the absence of bleeding, vascular risk factors, or vascular disease have a clear indication for aspirin in a regular dose. To determine whether 50 mg/day is as effective as 100 mg/day for the prophylaxis of microvascular circulation disturbances in essential thrombocythemia, a randomized trial comparing low-dose aspirin 50 mg versus 100 mg at platelet counts between 400 and 1,000 up to 1,500 x 10(9)/L is recommended. To address the question whether reduction of the platelet count to normal (< 350 x 10(9)/L) is as effective as low-dose aspirin for the long-term relief of microvascular circulation disturbances, a randomized study comparing low-dose aspirin with the correction of platelet count to normal by anagrelide is recommended. High-risk essential thrombocythemia patients have a clear indication for platelet reductive therapy, including: (a) platelets > 1,500 x 10(9)/L, history of major thrombosis (myocardial infarction, stroke, peripheral occlusive vascular disease), or presence of vascular disease (e.g., arteriosclerosis); (b) history or presence of spontaneous or major bleedings, bleedings elicited by low-dose aspirin for the secondary prevention of vascular complications in essential thrombocythemia at platelet counts < 1500 x 10(9)/L, and side effects of long-term aspirin treatment such as gastritis; and progression from low- to high-risk essential thrombocythemia patients during follow-up or progressive myeloproliferative disease such as significant splenomegaly, myelofibrosis, leukocytosis, etc. To address the question of optimal treatment of high-risk essential thrombocythemia patients, randomization for anagrelide versus interferon at < 65 years of age and anagrelide versus hydroxyurea at an age > 65 years is recommended.