The document summarizes essential thrombocytosis, a rare chronic blood disorder characterized by overproduction of platelets. It is one of four myeloproliferative disorders. The summary describes the epidemiology, pathophysiology involving abnormal megakaryocytes and platelet function, clinical features such as bleeding, thrombosis, and splenomegaly. Diagnostic criteria include persistent thrombocytosis over 600x109/L and exclusion of other causes, with some cases associated with a JAK2 kinase mutation. Treatment aims to reduce platelet count and risk of thrombosis.

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Myeloproliferative disease
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Myeloproliferative disease
The myeloproliferative diseases ("MPD"s)
Myeloproliferative disease
are a group of diseases of the bone
Classification and external resources
marrow in which excess cells are
ICD-10 D47.1 overview outline images locations
produced. They are related to, and may
ICD-9 205.1, 238.4, 289.89, 289.9
evolve into, myelodysplastic syndrome and Search this article
ICD-O: 9950/0-9964/3 high
acute myeloid leukemia, although the
MeSH D009196
myeloproliferative diseases on the whole
have a much better prognosis than these conditions. The concept of myeloproliferative Myeloproliferative disease
disease was first proposed in 1951 by the eminent hematologist William Dameshek.[1] Classification
In the most recent World Health Organization classification of Hematologic Causes
malignancies, this group of diseases was renamed from "myeloproliferative diseases" to Diagnosis
"myeloproliferative neoplasms". This reflects the underlying clonal genetic changes that References
are a salient feature of this group of disease. External links
Images Videos
Classification
Although not a malignant neoplasm like other cancers, MPDs are classified within the
hematological neoplasms.
There are four main myeloproliferative diseases, which can be further categorized by the
view all 24 view all 15
presence of the Philadelphia chromosome:
Philadelphia Chromosome "positive" Philadelphia Chromosome "negative"
Chronic myelogenous leukemia (CML) Polycythemia vera (PV)
Essential thrombocytosis (ET)
Myelofibrosis (MF)
In 2001, the World Health Organization classified "chronic eosinophilic leukemia /
hypereosinophilic syndrome" and chronic neutrophilic leukemia under "Chronic
myeloproliferative diseases". [2]
Causes
All MPDs arise from precursors of the "myeloid" lineage in the bone marrow. The
lymphoid lineage may produce similar diseases, the lymphoproliferative disorders (acute
lymphoblastic leukemia, lymphomas, chronic lymphocytic leukemia and multiple
myeloma).
Diagnosis
Depending on the nature of the myeloproliferative disorder, diagnostic tests may include
red cell mass determination (for polycythemia), bone marrow aspirate and trephine
biopsy, arterial oxygen saturation and carboxyhaemoglobin level, neutrophil alkaline
phosphatase level, vitamin B12 (or B12 binding capacity) and serum urate. [3]
According to the WHO Classification of Hematopoietic and Lymphoid Neoplasms 2008
myeloproliferative disorders are divided into the following by diagnostic characteristics:
1. Chronic myelogenous leukemia (CML) with defining translocation t(9;22) BCR-ABL
translocation which has three breakpoints:
a. u-BCR-ABL (p230): leads to CML with usual neutrophilia and
basophilia. b. minor-BCR-ABL (p190): leads to CML which has a tendency
to become acute lymphoblastic leukemia (ALL) usually precursor B ALL
and rarely precursor T ALL. c. major-BCR-ABL (p210): normal usual
breakpoint
2. Primary myelofibrosis associated with JAK2 mutation in up to 50% of cases and MPL
(thrombopoietin receptor) mutation in up to 5% of cases
a. Cellular phase - increased megakaryocytes which cluster, reticulin
fibrosis, later trichrome (collagenous) fibrosis, and increased myeloid

2. precursors b. Fibrotic phase - collagenous fibrosis with lack of marrow
elements
3. Polycythemia vera associated most often with JAK2 mutation in up to 80% of cases
a. Cellular phase - increased megakaryocytes which cluster, reticulin
fibrosis, later trichrome fibrosis, and increased myeloid and erythroid
precursors b. Fibrotic phase - collagenous fibrosis with lack of marrow
elements
4. Essential Thrombocythemia associated with JAK2 mutation in up to 20% of cases
and MPL (thrombopoietin receptor) mutation in up to 15% of cases
a. Cellular phase - increased large megakaryocytes with fibrosis and
little increase in other bone marrow elements b. Fibrotic phase -
collagenous fibrosis with lack of marrow elements
These disorders are still being revised according to more specific genetic mutations and
how often patients end in a fibrotic marrow event.
In 2005, the discovery of the JAK2 V617F mutation provided some evidence to suggest
a common pathogenesis for the Philadelphia Chromosome negative MPDs.[4][5][6][7][8]
References
1. ↑ Dameshek W (1951). "[Expression error: Missing operand for > Some speculations on the
myeloproliferative syndromes]". Blood 6 (4): 372–5. PMID 14820991.
2. ↑ "Classification of Human Hematopoietic Malignancies".
http://emice.nci.nih.gov/emice/mouse_models/organ_models/hema_models/hema_human_class.
3. ↑ Levene, Malcolm I.; Lewis, S. M.; Bain, Barbara J.; Imelda Bates (2001). Dacie & Lewis Practical
Haematology. London: W B Saunders. p. 586. ISBN 0-443-06377-X.
4. ↑ Baxter EJ, Scott LM, Campbell PJ, et al. (2005). "[Expression error: Missing operand for > Acquired
mutation of the tyrosine kinase JAK2 in human myeloproliferative disorders]". Lancet 365 (9464): 1054–
1061. doi:10.1016/S0140-6736(05)71142-9. PMID 15781101.
5. ↑ James C, Ugo V, Le Couedic JP, et al. (2005). "[Expression error: Missing operand for > A unique
clonal JAK2 mutation leading to constitutive signalling causes polycythaemia vera]". Nature 434 (7037):
1144–1148. doi:10.1038/nature03546. PMID 15793561.
6. ↑ Levine RL, Wadleigh M, Cools J, et al. (2005). "[Expression error: Missing operand for > Activating
mutation in the tyrosine kinase JAK2 in polycythemia vera, essential thrombocythemia, and myeloid
metaplasia with myelofibrosis]". Cancer Cell 7 (4): 387–397. doi:10.1016/j.ccr.2005.03.023. PMID
15837627.
7. ↑ Kralovics R, Passamonti F, Buser AS, et al. (2005). "[Expression error: Missing operand for > A gain-
of-function mutation of JAK2 in myeloproliferative disorders]". N Engl J Med 352 (17): 1779–1790.
doi:10.1056/NEJMoa051113. PMID 15858187.
8. ↑ Campbell PJ, Scott LM, Buck G, et al. (2005). "[Expression error: Missing operand for > Definition of
subtypes of essential thrombocythaemia and relation to polycythaemia vera based on JAK2 V617F
mutation status: a prospective study]". Lancet 366 (9501): 1945–1953. doi:10.1016/S0140-6736(05)67785-
9. PMID 16325696.
External links
Myeloproliferative Disorders Website of The CMPD Education Foundation
Myeloproliferative Disorders in practice
Myeloproliferative Disease Support List Free daily digest, 2850 subscribers 40+
countries
MeSH Myeloproliferative+Disorders
Myeloproliferative Disorders Research Consortium
MPD Foundation - Free newsletter and patient brochure
This disease article is a stub. You can help Wikipedia by expanding it.
Myeloid Hematological malignancy/leukemia histology (ICD-O 9590-9989, C81-C96, show
200-208)
Categories:
Disease stubs | Hematology
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What Are Myeloproliferative Disorders?
Quick Links Myeloproliferative disorders are a group of slow-growing blood cancers, including chronic myelogenous
leukemia, in which large numbers of abnormal red blood cells, white blood cells, or platelets grow and
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spread in the bone marrow and the peripheral blood.
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NCI Drug Dictionary The following PDQ treatment summaries are available:
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Childhood Acute Myeloid Leukemia/Other Myeloid Malignancies
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Includes childhood myelodysplastic syndromes and other myeloproliferative disorders.
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Subsections of this summary include:
NCI Highlights Polycythemia Vera
Office of Biorepositories and Chronic Idiopathic Myelofibrosis
Biospecimen Research Essential Thrombocythemia
The Nation's Investment in Chronic Neutrophilic Leukemia
Cancer Research FY 2010 Chronic Eosinophilic Leukemia
Report to the Nation Finds
Myelodysplastic Syndromes
Continued Declines in Cancer
Rates Includes refractory anemia, refractory anemia with excess blasts, refractory anemia with ringed
sideroblasts, refractory cytopenia with multilineage dysplasia, unclassifiable myelodysplastic syndrome,
and myelodysplastic syndrome associated with del (5q).
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Subsections of this summary include:
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Secondary Myelodysplastic Syndrome
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Myelodysplastic/Myeloproliferative Diseases
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Subsections of this summary include:
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Bing essential thrombocythemia
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Essential thrombocytosis
view original wikipedia article
Essential thrombocytosis
'Essential thrombocytosis (ET, also known
ICD10 = D75.2, D47.3
as essential thrombocythemia) is a rare
Classification and external resources
chronic blood disorder characterized by
ICD-9 238.71 overview outline images locations
the overproduction of platelets by
ICD-O: M9962/3
megakaryocytes in the bone marrow in Search this article
OMIM 187950 high
the absence of an alternative cause. In
DiseasesDB 4522
some cases this disorder may be
MedlinePlus 000543
progressive, and rarely may evolve into Essential thrombocytosis
eMedicine med/2266
acute myeloid leukemia or
MeSH D013920 Epidemiology
myelofibrosis. It is one of four
Pathophysiology
myeloproliferative disorders.
Clinical features
Epidemiology Diagnostic criteria
Treatment
Essential thrombocytosis is diagnosed at a rate of about 2 to 3 per 100,000 individuals Prognosis
annually. [1][2] The disease usually affects middle aged to elderly individuals, with an Special care related to pregnancy
average age at diagnosis of 50–60 years, although it can affect children and young References
adults as well. [3] External links
Images
Pathophysiology
The pathologic basis for this disease is unknown. However, essential thrombocytosis
resembles polycythemia vera in that cells of the megakaryocytic series are more
sensitive to growth factors. Platelets derived from the abnormal megakaryocytes do not
function properly, which contributes to the clinical features of bleeding and thrombosis. view all 24
In 2005, a mutation in the JAK2 kinase (V617F) was found by multiple research groups
[4][5][6] to be associated with essential thrombocytosis in around 30% of cases. JAK2 is
a member of the Janus kinase family. This mutation may be helpful in making a
diagnosis or as a target for future therapy.
Clinical features
The major symptoms are bleeding and thrombosis. Other symptoms include epistaxis
(nosebleeds) and bleeding from gums and gastrointestinal tract. One characteristic
symptom is throbbing and burning of the hands and feet due to the occlusion of small
arterioles by platelets (erythromelalgia). An enlarged spleen (splenomegaly) may be
found on examination.
Diagnostic criteria
The diagnosis of essential thrombocytosis requires the presence of a persistent
thrombocytosis of greater than 600 x109 /L in the absence of an alternative cause.
The following revised diagnostic criteria for essential thrombocytosis were proposed in
2005 [7] . The diagnosis requires the presence of both A criteria together with B3 to B6,
or of criterion A1 together with B1 to B6.
A1. Platelet count > 600 x 10 9 /L for at least 2 months
A2. Acquired V617F JAK2 mutation present
B1. No cause for a reactive thrombocytosis
normal inflammatory indices
B2. No evidence of iron deficiency
stainable iron in the bone marrow or normal red cell mean corpuscular
volume
B3. No evidence of polycythemia vera

6. hematocrit < midpoint of normal range or normal red cell mass in presence
of normal iron stores
B4. No evidence of chronic myeloid leukemia
But the Philadelphia chromosome may be present in up to 10% of cases. Patients with
the Philadelphia chromosome have a potential for the development of acute leukemia,
especially acute lymphocytic leukemia.
B5. No evidence of myelofibrosis
no collagen fibrosis and ≤ grade 2 reticulin fibrosis (using 0–4 scale)
B6. No evidence of a myelodysplastic syndrome
no significant dysplasia
no cytogenetic abnormalities suggestive of myelodysplasia
Treatment
Not all patients will require treatment at presentation. In those who are at increased risk
of thrombosis or bleeding (older age, prior history of bleeding or thrombosis, or very
high platelet count), reduction of the platelet count to the normal range can be achieved
using hydroxyurea (also known as hydroxycarbamide), interferon-α or anagrelide. Low-
dose aspirin is widely used to reduce the risk of thrombosis, but there may be an
increased risk of bleeding if aspirin is initiated while the platelet count is very high.
The PT1 study [8] compared hydroxyurea in combination with aspirin to anagrelide in
combination with Aspirin as initial therapy for essential thrombocytosis. Hydroxyurea
was superior, with lower risk of arterial thrombosis, lower risk of severe bleeding and
lower risk of transformation to myelofibrosis (although the rate of venous thrombosis
was higher with hydroxycarbamide than with anagrelide).
In rare cases where patients have life-threatening complications, the platelet count can
be reduced rapidly using platelet apheresis (a procedure that removes platelets from the
blood directly). ...
Prognosis
Essential thrombocytosis is sometimes described as a slowly progressive disorder with
long asymptomatic periods punctuated by thrombotic or hemorrhagic events.
However, well-documented medical regimes 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.
Special care related to pregnancy
Hydroxyurea and anagrelide are contraindicated during pregnancy and nursing. There is
current debate as to the safety of interferon during pregnancy and nursing. Essential
thrombocytosis can be linked with increased risk of spontaeous abortion or miscarriage
in the first trimester of pregnancy. Throughout pregnancy, close monitoring of the
mother for thrombosis and placenta is recommended to ensure blood clots are caught.
Post partum, often daily injections of low dose low molecular weight heparin (e.g.
enoxaparin) are prescribed for several weeks as this is a period where the mother is at
higher risk of developing a blood clot.
References
1. ↑ Mesa R, Silverstein M, Jacobsen S, Wollan P, Tefferi A (1999). "[Expression error: Missing operand
for > Population-based incidence and survival figures in essential thrombocythemia and agnogenic myeloid
metaplasia: an Olmsted County Study, 1976-1995]". Am J Hematol 61 (1): 10–5. doi:10.1002/(SICI)1096-
8652(199905)61:1<10::AID-AJH3>3.0.CO;2-I. PMID 10331505.
2. ↑ Kutti J, Ridell B (2001). "[Expression error: Missing operand for > Epidemiology of the
myeloproliferative disorders: essential thrombocythaemia, polycythaemia vera and idiopathic myelofibrosis]".
Pathol Biol (Paris) 49 (2): 164–6. PMID 11317963.
3. ↑ Hoffman: Hematology: Basic Principles and Practice, 4th ed., 2005 Churchill Livingstone, Chapter 71.
4. ↑ Kralovics R, Passamonti F, Buser AS, Teo SS, et al. (2005). "[Expression error: Missing operand for >
A gain-of-function mutation of JAK2 in myeloproliferative disorders]". N Engl J Med 352 (17): 1779–90.
doi:10.1056/NEJMoa051113. PMID 15858187.
5. ↑ Baxter EJ, Scott LM, Campbell PJ, et al. (2005). "Acquired mutation of the tyrosine kinase JAK2 in
human myeloproliferative disorders". Lancet 365 (9464): 1054–61. doi:10.1016/S0140-6736(05)71142-9.
PMID 15781101. http://linkinghub.elsevier.com/retrieve/pii/S0140-6736(05)71142-9.

7. 6. ↑ Levine RL, Wadleigh M, Cools J, et al. (2005). "Activating mutation in the tyrosine kinase JAK2 in
polycythemia vera, essential thrombocythemia, and myeloid metaplasia with myelofibrosis". Cancer Cell 7
(4): 387–97. doi:10.1016/j.ccr.2005.03.023. PMID 15837627.
http://linkinghub.elsevier.com/retrieve/pii/S1535-6108(05)00094-2.
7. ↑ Campbell PJ, Green AR (2005). "Management of polycythemia vera and essential thrombocythemia".
Hematology Am Soc Hematol Educ Program 2005: 201–8. doi:10.1182/asheducation-2005.1.201. PMID
16304381. http://www.asheducationbook.org/cgi/pmidlookup?view=long&pmid=16304381.
8. ↑ Harrison CN, Campbell PJ, Buck G, et al. (2005). "Hydroxyurea compared with anagrelide in high-risk
essential thrombocythemia". N. Engl. J. Med. 353 (1): 33–45. doi:10.1056/NEJMoa043800. PMID
16000354. http://content.nejm.org/cgi/pmidlookup?view=short&pmid=16000354&promo=ONFLNS19.
External links
Cancerbackup Essential Thrombocytosis page
CMPD Education Foundation
Pathology: hematology · hematologic diseases of RBCs and megakaryocytes / show
MEP (D50-69,74, 280-287)
Categories:
Hematology | Blood disorders
History
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All Wikipedia content is licensed under the GNU Free Document License or the Creative
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Go to Bing in English © 2010 Microsoft | Προστασία προσωπικών δεδομένων | Νομικές ανακοινώσεις | Βοήθεια