Refers to the presence of high platelet counts in the blood, and can be either reactive or primary.

Can predispose to thrombosis in some patients, but is usually asymptomatic.

A platelet the count of 450,000 per cubic millimeter or greater has a reported prevalence of 1.9% of ambulatory patients who are 65 years of age or older.

Extreme thrombocytosis of platelet count of 1,000,000 per millimeter or more is infrequent, and occurs in less than 2% of patients in large retrospective studies involving patients with thrombocytosis.

In patients with extreme thrombocytosis approximately 1 3rd have hematologic malignancies.

A normal platelet count ranges from 150,000 and 450,000 per mm³ (or microlitre) (150–450 x 109/L).

A retrospective study showed that adult patient with thrombocytosis primary thrombocytosis, a myeloproliferative neoplasm was observed in 5.2% of cases, secondary causes are infection 48%, trauma or postsurgical state 25%, other cancers 10.7%, and iron deficiency 7.4%.

Approximately 40% of patients with unexplained high platelet counts, will have cancer, and a platelet count higher than 450,000/mL is significant and should raise the consideration of the presence of such a lesion.

Healthy individuals make about 100 billion platelets daily to maintain homeostasis, and in patients with cancer make 5 to 10 times the normal level.

Often associated with an inflammatory disease, as the principal stimulant of platelet production, thrombopoietin, is elevated in these clinical states as part of the acute phase reaction.

Can occur in patients with myeloproliferative diseases.

Platelets are highly reactive cellular effectors hemostasis, immunity, and inflammation.

Platelets may actively promote cancer progression by protecting cancer cells from immune surveillance, arresting cancer cells in the microvascular and stimulation of angiogenesis.

Almost 40% of patients with incidental thrombocytosis exceeding 400,000 per cubic millimeter, in the absence of iron deficiency and benign inflammatory conditions, have an occult cancer, most commonly lung, breast, gastrointestinal, or ovarian cancer (Levin J et al).

2 major causes of thrombocytosis: reactive and clonal.

Reactive causes include transient processes such as acute bleeding, rebound from thrombocytopenia, acute infection, acute inflammation, extreme physical exertion, and stress.

Sustained reactive thrombocytosis seen in iron deficiency, hemolytic anemia, asplenia, cancer, chronic inflammation, infectious diseases, and drug reactions.

Among patients with thrombocytosis 80-90% have reactive thrombocytosis.

Increased thrombopoietic cytokine production by tumor cells and both cells is a major reason for paraneoplastic thrombocytosis.

Paraneoplastic thrombocytosis is mediated by hepatic thrombopoietin synthesis that is increased in response to excessive tumor derived interleukin-6, increasing platelet counts, which in turn promote tumor growth.

About one third of women with ovarian cancer have an abnormally high platelet count at the time of diagnosis.

Thrombocytosis is also seen with cancers of the lung, G.I. tract or breast.

Increase platelet counts can be due to a number of disease processes: essential thrombocytosis, other myeloproliferative disorders such as chronic myelogenous leukemia, polycythemia vera, myelofibrosis, reactive to inflammation, surgery, splenectomy, hyposplenism, asplenism, hemorrhage and iron deficiency, treatmenr with thrombopoietin agents, Kawasaki disease, soft tissue sarcoma, osteosarcoma, Inflammatory bowel disease, rheumatoid arthritis, nephritis, nephrotic syndrome, bacterial infections.

Often, no treatment is required or necessary for reactive thrombocytosis, however, in primary thrombocytosis, if platelet counts are over 750,000 or 1,000,000, and especially if there are other risk factors for thrombosis.

Aspirin at low doses is thought to be protective, and extreme levels are treated with hydroxyurea.

Anagrelide (Agrylin) has recently been introduced for the treatment of essential thrombocytosis however, recent studies show that anegrilide is not significantly more effective than traditionally used hydroxyurea,

Associated with deep venous thrombosis, pulmonary embolism, stroke, myocardial infarction, or hemorrhage.

Associated with paresthesias, dizziness, headaches, and visual disturbances.

May be associated with sepsis.

Accurate diagnosis is important for prognostication and the therapy.

The presence of a clonal marker such as JAK2 or MPL present in the majority of patients with essential thrombocytosis, polycythemia rubra vera, or primary of myelofibrosis, can reliably exclude reactive thrombocytosis.

Clonal thrombocytosis is the second most common category of thrombocytosis.

Clonal thrombocytosis typically due to chronic myeloproliferative disease including: polycythemia Vera, essential thrombocytosis, myelofibrosis, and CML.

Myelodysplastic syndrome may be associated with thrombocytosis.

In chronic myelogenous leukemia and refractory anemia with ring sideroblasts and marked thrombocytosis are associated with BCR/ABL and dyserythropoiesis, respectively.

Adrenalin can cause platelet elevations, probably due to demargination of platelets in the pulmonary vasculature.

Vinca alkaloids hy can induce thrombocytosis through their thrombocyte-stimulating properties.

Miconazole has been implicated in causing thrombocytosis.

Iron, can cause a transient thrombocytosis.

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