Essential thrombocytosis

Essential thrombocythaemia
Classification and external resources
Specialty oncology
ICD-10 D75.2, D47.3
ICD-9-CM 238.71
ICD-O M9962/3
OMIM 187950
DiseasesDB 4522
MedlinePlus 000543
eMedicine med/2266
MeSH D013920

Essential thrombocythaemia (ET; also known as essential thrombocytosis, essential thrombocythemia, primary thrombocytosis) is a rare chronic blood disorder characterised by the overproduction of platelets by megakaryocytes in the bone marrow.[1] It may, albeit rarely, develop into acute myeloid leukaemia or myelofibrosis.[1] It is one of four myeloproliferative disorders (disorders characterised by increased production of a particular line of blood cell).[1]

Signs and symptoms

Most people with ET are without symptoms referable to ET at the time of diagnosis, which is usually ultimately made after noting an elevated platelet level on a routine complete blood count (CBC).[2] The most common symptoms are bleeding, blood clots, headache, nausea, vomiting, abdominal pain, visual disturbances, dizziness, fainting, and numbness in the extremities; the most common signs are increased white blood cell count, reduced red blood cell count, and enlarged spleen.[2][3][4]

Cause

In ET, megakaryocytes are more sensitive to growth factors [citation needed]. Platelets derived from the abnormal megakaryocytes are activated, which, along with the elevated platelet count, contributes to the likelihood of thrombosis.[5] The increased possibility of bleeding when the platelet count is over 1 million is due to von Willibrand factor (vWF) sequestration by the increased mass of platelets, leaving insufficient vWF for platelet adhesion.[5] A mutation in the JAK2 kinase (V617F) is present in 40–50% of cases:[1][5] it is diagnostic. JAK2 is a member of the Janus kinase family.[1][5]

In 2013, two groups detected calreticulin mutations in a majority of JAK2-negative/MPL-negative patients with essential thrombocytosis and primary myelofibrosis, which makes CALR mutations the second most common in myeloproliferative neoplasms. All mutations (insertions or deletions) affected the last exon, generating a reading frame shift of the resulting protein, that creates a novel terminal peptide and causes a loss of endoplasmic reticulum KDEL retention signal.[6][7]

Diagnostic criteria

The following revised diagnostic criteria for essential thrombocythaemia were proposed in 2005.[8] The diagnosis requires the presence of both A criteria together with B3 to B6, or of criterion A1 together with B1 to B6.[9] The criteria is as follows:[9]

Treatment

Indications

Not all those affected will require treatment at presentation.[10][11][12] People are usually split up into low and high risk for bleeding/blood clotting groups (based on their age, their medical history, their blood counts and their lifestyles), low risk individuals are usually treated with aspirin, whereas those at high risk are given hydroxycarbamide and/or other treatments that reduce platelet count (such as interferon-α and anagrelide).[1][10][11][12]

Agents

Hydroxycarbamide, interferon-α and anagrelide can lower the platelet count. Low-dose aspirin is used to reduce the risk of thrombosis unless the platelet count is very high, where there is a risk of bleeding from the disease and hence this measure would be counter-productive (as they increase one's risk for bleeds).[1][10][11][12]

The PT1 study compared hydroxyurea plus aspirin to anagrelide plus aspirin as initial therapy for ET. Hydroxyurea treated patients had a lower incidence of arterial thrombosis, lower incidence of severe bleeding and lower incidence of transformation to myelofibrosis, but the risk of venous thrombosis was higher with hydroxycarbamide than with anagrelide. It is unknown whether the results are applicable to all ET patients.[1][10][11][12]

Prognosis

Essential thrombocytosis is sometimes described as a slowly progressive disorder with long asymptomatic periods punctuated by thrombotic or haemorrhagic events.[10] However, well-documented medical regimens can reduce and control the number of platelets, which reduces the risk of these thrombotic or haemorrhagic events. The lifespan of a well controlled ET person is well within the expected range for a person of similar age but without ET.[10]

Epidemiology

The incidence of ET is 0.6-2.5/100,000 per year, the median age at onset is 65–70 years and it is more frequent in females than in males.[13] The incidence in children is 0.09/100,000 per year.[13]

Pregnancy

Hydroxycarbamide and anagrelide are contraindicated during pregnancy and nursing.[14] Essential thrombocytosis can be linked with a three-fold increase in risk of miscarriage.[13] Throughout pregnancy, close monitoring of the mother and foetus is recommended.[14] Low-dose low molecular weight heparin (e.g. enoxaparin) may be used.[14] For life-threatening complications, the platelet count can be reduced rapidly using platelet apheresis, a procedure that removes platelets from the blood and returns the remainder to the patient.[14]

References

  1. 1 2 3 4 5 6 7 8 Beer, PA; Green, AR (2009). "Pathogenesis and management of essential thrombocythemia" (PDF). Hematology / the Education Program of the American Society of Hematology. American Society of Hematology. Education Program: 621–8. doi:10.1182/asheducation-2009.1.621. PMID 20008247.
  2. 1 2 Fu, R; Zhang, L; Yang, R (November 2013). "Paediatric essential thrombocythaemia: clinical and molecular features, diagnosis and treatment". British Journal of Haematology 163 (3): 295–302. doi:10.1111/bjh.12530. PMID 24032343.
  3. ↑ Frewin, R; Dowson, A (October 2012). "Headache in essential thrombocythaemia." (PDF). International Journal of Clinical Practice 66 (10): 976–83. doi:10.1111/j.1742-1241.2012.02986.x. PMC 3469735. PMID 22889110.
  4. ↑ Tefferi, A (March 2011). "Annual Clinical Updates in Hematological Malignancies: a continuing medical education series: polycythemia vera and essential thrombocythemia: 2011 update on diagnosis, risk-stratification, and management.". American Journal of Hematology 86 (3): 292–301. doi:10.1002/ajh.21946. PMID 21351120.
  5. 1 2 3 4 Vannucchi, AM (June 2010). "Insights into the pathogenesis and management of thrombosis in polycythemia vera and essential thrombocythemia". Internal and Emergency Medicine 5 (3): 177–84. doi:10.1007/s11739-009-0319-3. PMID 19789961.
  6. ↑ Nangalia J, Massie CE, Baxter EJ, Nice FL, Gundem G, Wedge DC, Avezov E, Li J, Kollmann K, Kent DG, Aziz A, Godfrey AL, Hinton J, Martincorena I, Van Loo P, Jones AV, Guglielmelli P, Tarpey P, Harding HP, Fitzpatrick JD, Goudie CT, Ortmann CA, Loughran SJ, Raine K, Jones DR, Butler AP, Teague JW, O'Meara S, McLaren S, Bianchi M, Silber Y, Dimitropoulou D, Bloxham D, Mudie L, Maddison M, Robinson B, Keohane C, Maclean C, Hill K, Orchard K, Tauro S, Du MQ, Greaves M, Bowen D, Huntly BJ, Harrison CN, Cross NC, Ron D, Vannucchi AM, Papaemmanuil E, Campbell PJ, Green AR (Dec 2013). "Somatic CALR mutations in myeloproliferative neoplasms with nonmutated JAK2". The New England Journal of Medicine 369 (25): 2391–405. doi:10.1056/NEJMoa1312542. PMC 3966280. PMID 24325359.
  7. ↑ Klampfl T, Gisslinger H, Harutyunyan AS, Nivarthi H, Rumi E, Milosevic JD, Them NC, Berg T, Gisslinger B, Pietra D, Chen D, Vladimer GI, Bagienski K, Milanesi C, Casetti IC, Sant'Antonio E, Ferretti V, Elena C, Schischlik F, Cleary C, Six M, Schalling M, Schönegger A, Bock C, Malcovati L, Pascutto C, Superti-Furga G, Cazzola M, Kralovics R (Dec 2013). "Somatic mutations of calreticulin in myeloproliferative neoplasms". The New England Journal of Medicine 369 (25): 2379–90. doi:10.1056/NEJMoa1311347. PMID 24325356.
  8. ↑ Campbell PJ, Green AR (2005). "Management of polycythemia vera and essential thrombocythemia" (PDF). Hematology / the Education Program of the American Society of Hematology 2005: 201–8. doi:10.1182/asheducation-2005.1.201. PMID 16304381.
  9. 1 2 Vardiman, JW; Thiele, J; Arber, DA; Brunning, RD; Borowitz, MJ; Porwit, A; Harris, NL; Le Beau, MM; Hellström-Lindberg, E; Tefferi, A; Bloomfield, CD (July 2009). "The 2008 revision of the World Health Organization (WHO) classification of myeloid neoplasms and acute leukemia: rationale and important changes." (PDF). Blood 114 (5): 937–51. doi:10.1182/blood-2009-03-209262. PMID 19357394.
  10. 1 2 3 4 5 6 Cervantes, F (2011). "Management of essential thrombocythemia." (PDF). Hematology / the Education Program of the American Society of Hematology 2011: 215–21. doi:10.1182/asheducation-2011.1.215. PMID 22160037.
  11. 1 2 3 4 Birgegård, G (July 2013). "Pharmacological management of essential thrombocythemia.". Expert Opinion on Pharmacotherapy 14 (10): 1295–306. doi:10.1517/14656566.2013.797408. PMID 23668666.
  12. 1 2 3 4 Tefferi, A; Barbui, T (August 2013). "Personalized management of essential thrombocythemia-application of recent evidence to clinical practice." (PDF). Leukemia 27 (8): 1617–20. doi:10.1038/leu.2013.99. PMC 3740400. PMID 23558521.
  13. 1 2 3 Fabris, F; Randi, ML (October 2009). "Essential thrombocythemia: past and present.". Internal and Emergency Medicine 4 (5): 381–8. doi:10.1007/s11739-009-0284-x. PMID 19636672.
  14. 1 2 3 4 Valera, MC; Parant, O; Vayssiere, C; Arnal, JF; Payrastre, B (October 2011). "Essential thrombocythemia and pregnancy". European Journal of Obstetrics, Gynecology, and Reproductive Biology 158 (2): 141–7. doi:10.1016/j.ejogrb.2011.04.040. PMID 21640467.

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