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Key Features

Essentials of Diagnosis

  • JAK2 V617F mutation

  • Splenomegaly

  • Normal arterial oxygen saturation

  • Usually elevated white blood count and platelet count

General Considerations

  • Characterized by autonomous overproduction of erythroid cells, but causes overproduction of all hematopoietic cell lines

Demographics

  • 60% of patients are men

  • Median age at presentation is 60 years

  • Rarely occurs in persons under age 40 years

Clinical Findings

Symptoms and Signs

  • Common complaints related to expanded blood volume and increased blood viscosity include

    • Headache

    • Dizziness

    • Tinnitus

    • Blurred vision

    • Fatigue

  • Generalized pruritus is related to histamine release from basophils

  • Epistaxis is probably related to engorgement of mucosal blood vessels in combination with abnormal hemostasis

  • Thrombosis

    • Appears to be related both to increased blood viscosity and abnormal platelet function

    • Incidence of thrombotic complications of surgery is very high if polycythemia is uncontrolled; elective surgery should be deferred until the condition has been treated

  • Increased bleeding can also occur

  • Physical examination reveals plethora and engorged retinal veins

Differential Diagnosis

  • Spurious polycythemia may be related to diuretic use or may occur without obvious cause

  • Suspect secondary causes of polycythemia if

    • Splenomegaly is absent

    • Elevated hematocrit is not accompanied by increases in other cell lines

  • Secondary causes of polycythemia include

    • Hypoxia: cardiac disease, pulmonary disease, high altitude

    • Carboxyhemoglobin: smoking

    • Kidney lesions

    • Erythropoietin-secreting tumors (rare)

    • Abnormal hemoglobins (rare)

  • Polycythemia vera should be differentiated from other myeloproliferative disorders (Table 13–14)

Table 13–14.Laboratory features of myeloproliferative neoplasms.

Diagnosis

Laboratory Findings

  • Hematocrit (at sea level) that exceeds 49% in males or 48% in females

  • RBCs

    • RBC morphology is normal at presentation (Table 13–14)

      • However, microcytosis, hypochromia, and poikilocytosis may result from iron deficiency following treatment by phlebotomy

    • RBC mass is elevated

  • White blood cells

    • Usually normal morphology, though basophilia and eosinophilia are frequently present

    • Count is usually elevated to 10,000–20,000/mcL

  • Platelets

    • Morphology is usually normal

    • Count is variably increased, sometimes to counts exceeding 1,000,000/mcL

  • Erythropoietin levels are suppressed

  • Bone marrow

    • Hypercellular, with panhyperplasia of all hematopoietic elements

    • Iron stores are usually absent

  • Vitamin B12 levels are strikingly elevated because of increased levels of transcobalamin III

  • Overproduction of uric acid may lead to hyperuricemia

  • Progressive hypersplenism may also lead to elliptocytosis

  • Confirm diagnosis with JAK2 mutation screening

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