Thrombocythemia

Thrombocythemia, also called thrombocytosis, is the presence of a high platelet (thrombocyte) count in the blood. In a healthy individual, a normal platelet count ranges from 150,000 and 450,000 per microlitre (mm3), or 150–450 x 109/litre).[1] These limits, however, are determined by the 2.5th lower and upper percentile, and a mild elevation does not necessary imply any form of disease. .

Thrombocythemia
Other namesThrombocytosis. thrombophilia
SpecialtyHematology 

Causes are divided into primary, also termed essential thrombocythemia; secondary, also termed reactive thrombocythemia; and artifactual. Thrombocythemia is usually symptomless, and is therefore diagnosed from a routine complete blood count, which includes a platelet count. Thrombocythemia may predispose to thrombosis.


Signs and symptoms

High platelet levels are often without signs or symptoms, and are first noted on a routine complete blood count.

A very small segment of patients report symptoms of erythromelalgia, a burning sensation and redness of the extremities that resolves with cooling and/or aspirin use.[2]

Scientific literature sometimes excludes thrombocytosis from the scope of thrombophilia by definition,[3] but practically, by the definition of thrombophilia as an increased predisposition to thrombosis,[4][5] thrombocytosis (especially primary thrombocytosis) is a potential cause of thrombophilia. Conversely, secondary thrombocytosis very rarely causes thrombotic complications.[6]

Evaluation

However, it is important that a full medical history be elicited to ensure that the increased platelet count is not due to a secondary process. Often, it occurs in tandem with an inflammatory disease, as the principal stimulants of platelet production (e.g. thrombopoietin) are elevated in these clinical states as part of the acute phase reaction.

Causes

Reactive

Reactive thrombocythemia is the common cause of high platelet count. It accounts for 88% to 97% of thrombocythemia cases in adults, and 100% in children. In adults, acute infection, tissue damage, chronic inflammation and malignancy are the common causes of reactive thrombocythemia. Usually, one or more of these conditions is present in more than 75% of the cases with reactive thrombocythemia. Causes for reactive thrombocytopenia in children are similar to adults. In addition to that, haemolytic anemia and thalassemia are often present in children living in the middle eastern countries. Other causes of reactive thrombocythemia includes: post surgery, iron deficiency, drugs, and rebound effect after bone marrow suppression.[7]

Clonal

Once the reactive causes of thrombocythemia are ruled out, clonal thrombocythemia should be considered. The most common cause of clonal thrombocythemia is myeloproliferative disease. These include: essential thrombocythemia, chronic myelogenous leukemia, polycythemia vera, and primary myelofibrosis.[7]

Artifactual

Extremely rare causes of thrombocythemia are artifactual causes. This is due to the presence of structures resembling platelets in the blood such as needle-like cryoglobulin crystals, cytoplasmic fragments of circulating leukemic cells, bacteria, and red blood cell microvesicles. These structures are counted as platelets by the automated machine counter; therefore, causing the platelet number to be falsely elevated. However, such error can be avoided by doing a peripheral blood smear.[7]

Diagnosis

Laboratory tests might include: complete blood count, liver enzymes, renal function and erythrocyte sedimentation rate.

If the cause for the high platelet count remains unclear, bone marrow biopsy is often undertaken, to differentiate whether the high platelet count is reactive or essential.

Treatment

Often, no treatment is required or necessary for reactive thrombocytosis. In cases of reactive thrombocytosis of more than 1,000x109/L, it may be considered to administer daily low dose aspirin (such as 65 mg) to minimize the risk of stroke or thrombosis.[8]

However, in essential thrombocythemia, if platelet counts are over 750,000 or 1,000,000, and especially if there are other risk factors for thrombosis, treatment may be needed. Selective use of aspirin at low doses is thought to be protective. Extremely high platelet counts can be treated with hydroxyurea (a cytoreducing agent) or anagrelide (Agrylin).[9]

In Janus kinase 2 positive disorders, ruxolitinib (Jakafi) can be effective.

References
  • Schafer AI (March 2004). "Thrombocytosis". N. Engl. J. Med. 350 (12): 1211–9. doi:10.1056/NEJMra035363. PMID 15028825.
  1. Kumar & Clark (2005). "8". Clinical Medicine (Sixth ed.). Elsevier Saunders. p. 469. ISBN 0-7020-2763-4.
  2. van Genderen, P. J.; Lucas, I. S.; van Strik, R.; Vuzevski, V. D.; Prins, F. J.; van Vliet, H. H.; Michiels, J. J. (1996-09-01). "Erythromelalgia in essential thrombocythemia is characterized by platelet activation and endothelial cell damage but not by thrombin generation". Thrombosis and Haemostasis. 76 (3): 333–338. doi:10.1055/s-0038-1650579. ISSN 0340-6245. PMID 8883266.
  3. "Management of patients with thrombophilia". Drug and Therapeutics Bulletin. 33 (1): 6–8. 1995. doi:10.1136/dtb.1995.3316. PMID 7587981.
  4. Mitchell RS, Kumar V, Abbas AK, Fausto N (2007). "Chapter 4". Robbins Basic Pathology (Eighth ed.). Philadelphia: Saunders. ISBN 978-1-4160-2973-1.
  5. Heit JA (2007). "Thrombophilia: common questions on laboratory assessment and management". Hematology Am. Soc. Hematol. Educ. Program. 2007 (1): 127–35. doi:10.1182/asheducation-2007.1.127. PMID 18024620.
  6. Pediatric Thrombocytosis at eMedicine
  7. Jonathan, S Bleeker; William, J Hogan (8 June 2011). "Thrombocytosis: Diagnostic Evaluation, Thrombotic Risk Stratification, and Risk-Based Management Strategies". Thrombosis. 2011: 536062. doi:10.1155/2011/536062. PMC 3200282. PMID 22084665.
  8. Secondary Thrombocytosis~treatment at eMedicine
  9. Harrison, CN; Campbell PJ; Buck G; Wheatley K; East CL; Bareford D; Wilkins BS; van der Walt JD; Reilly JT; Grigg AP; Revell P; Woodcock BE; Green AR; United Kingdom Medical Research Council Primary Thrombocythemia 1 Study (2005). "Hydroxyurea compared with anagrelide in high-risk essential thrombocythemia". NEJM. 353 (1): 33–45. doi:10.1056/NEJMoa043800. PMID 16000354.
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