Semin Thromb Hemost 2006; 32(3): 174-207
DOI: 10.1055/s-2006-939431
Copyright © 2006 by Thieme Medical Publishers, Inc., 333 Seventh Avenue, New York, NY 10001, USA.

Clinical and Laboratory Features, Pathobiology of Platelet-Mediated Thrombosis and Bleeding Complications, and the Molecular Etiology of Essential Thrombocythemia and Polycythemia Vera: Therapeutic Implications

Jan J. Michiels1 , 5 , Zwi Berneman1 , Dirk Van Bockstaele2 , Marc van der Planken3 , Hendrik De Raeve4 , Wilfried Schroyens1
  • 1Department of Hematology, University Hospital Antwerp, Belgium
  • 2Laboratory of Molecular Diagnostics, University Hospital Antwerp, Belgium
  • 3Laboratory of Hematology and Hemostasis, University Hospital Antwerp, Belgium
  • 4Department of Pathology, University Hospital Antwerp, Belgium
  • 5Hematology, Hemostasis and Thrombosis Science Center, Goodheart Institute, Rotterdam, The Netherlands
Further Information

Publication History

Publication Date:
02 May 2006 (online)

ABSTRACT

Microvascular disturbances in essential thrombocythemia (ET) and polycythemia vera (PV), including erythromelalgia, and atypical and typical transient cerebral, ocular, and coronary ischemic attacks, are caused by platelet-mediated transient and occlusive thrombosis in the end-arterial circulation. ET patients with microvascular disturbances have shortened platelet survival, increased β-thromboglobulin (β-TG), platelet factor 4 (PF4), and thrombomodulin (TM) levels, and increased urinary thromboxane B2 (TXB2) excretion, indicating platelet-mediated thrombotic processes. Inhibition of platelet cyclooxygenase-1 by aspirin is followed by relief of microvascular disturbances; correction of shortened platelet survival; correction of increased plasma β-TG, PF4, and TM levels; and correction of increased TXB2 excretion to normal. In PV associated with thrombocythemia, increased hematocrit and whole blood viscosity aggravate the platelet-mediated microvascular syndrome of thrombocythemia to produce major arterial and venous thrombotic complications. Correction of hematocrit to normal by phlebotomy will reduce 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 ET and PV patients, in addition to phlebotomy, are obtained by treatment with aspirin and not with coumarin. The discovery of JAK2 V617F gain of function mutation in patients with myeloproliferative disorders (MPDs) expands our insights into the molecular etiology and biological features of ET, PV, and chronic idiopathic myelofibrosis (CIMF). The current concept is that heterozygous JAK2 V617F mutation with increased kinase activity is enough for megakaryocyte proliferation and increased hypersensitive platelets with no or slightly increased erythropoiesis in ET and in early PV mimicking ET. Homozygous JAK2 mutation with pronounced kinase activity is associated with trilinear megakaryocyte, erythroid, and granulocytic myeloproliferation, myeloid metaplasia, and secondary myelofibrosis (MF), with the most frequent clinical picture of classical PV complicated by major thrombosis in addition to the platelet-mediated microvascular thrombotic syndrome of thrombocythemia. The positive predictive value of a JAK2 V617F polymerase chain reaction test for the diagnosis of MPDs is high (near to 100%), but only half of ET and MF (sensitivity 50%) and the majority of PV (sensitivity 85 to 97%) are JAK2 V617F positive. Bone marrow histopathology, when used in combination with specific markers such as serum erythropoietin, PRV-1, endogenous erythroid colony formation, peripheral blood parameters and red cell mass, has a high sensitivity and specificity (near 100%) to detect the early and overt stages of the MPDs and to differentiate between ET, PV, and CIMF in both JAK2 V617F-positive and -negative MPDs.

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Jan Jacques MichielsM.D. Ph.D. 

Goodheart Institute, MPD Center Europe, Erasmus Tower, Veenmos 13

3069 AT Rotterdam, The Netherlands

Email: postbus@goodheartcenter.demon.nl