Skip to Main Content

We have a new app!

Take the Access library with you wherever you go—easy access to books, videos, images, podcasts, personalized features, and more.

Download the Access App here: iOS and Android. Learn more here!

For further information, see CMDT 13-25: Essential Thrombocytosis

Key Features

Essentials of Diagnosis

  • Elevated platelet count in absence of other causes

  • Normal red blood cell mass

  • Absence of bcr/abl gene (Philadelphia chromosome)

General Considerations

  • An uncommon myeloproliferative disorder of unknown cause

  • Characterized by marked proliferation of the megakaryocytes in the bone marrow, leading to elevation of the platelet count

  • High frequency of mutations of JAK2 and others (see also Polycythemia Vera)


  • The median age at presentation is 50–60 years

  • There is a slightly increased incidence in women

Clinical Findings

Symptoms and Signs

  • Elevated platelet count

  • Thrombosis

    • Most common clinical problem

    • Risk rises with age

    • Venous thromboses may occur in unusual sites, such as the mesenteric, hepatic, or portal vein

  • Erythromelalgia: characterized by painful burning of the hands accompanied by erythema

  • Bleeding

    • Typically mucosal

    • Uncommon occurrence

    • Related to a concomitant qualitative platelet defect

  • Splenomegaly is present in at least 25% of patients

Differential Diagnosis

  • Must distinguish from reactive causes of thrombocytosis (platelet count seldom is > 1,000,000/mcL [1000 × 109/L])

    • Inflammatory disorders, such as rheumatoid arthritis and ulcerative colitis

    • Iron deficiency

  • Other myeloproliferative disorders

    • Polycythemia vera

    • Myelofibrosis

    • Chronic myeloid leukemia (CML)

  • MPL and CALR mutations frequently occur in patients with JAK2-negative essential thrombocytosis


Laboratory Findings

  • Elevated platelet count (may be > 2,000,000/mcL [2000 × 109/L]) (Table 13–14)

  • Mildly elevated white blood cell count (usually not above 30,000/mcL [30 × 109/L]), but with some immature myeloid forms

  • Hematocrit is normal

  • Peripheral blood smear

    • Reveals large platelets

    • Giant degranulated forms seen in myelofibrosis are not observed

  • Red blood cell morphology is normal

  • Bone marrow shows increased numbers of megakaryocytes but no other morphologic abnormalities

  • Peripheral blood should be tested for the bcr/abl fusion gene (Philadelphia chromosome) because it can differentiate between CML, where it is present, and essential thrombocytosis, where it is absent

Table 13–14.Laboratory features of myeloproliferative neoplasms.


  • Strict control of coexistent cardiovascular risk factors is mandatory for all patients

  • Control of the platelet count, which should be kept at < 500,000/mcL (500 × 109/L), reduces ...

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.