Essential Thrombocythemia

Peripheral Blood Smear

Bone Marrow Aspirate

Bone Marrow Aspirate, Dry Tap

Bone Marrow Biopsy

Bone Marrow Biopsy, High Power

• Clonal stem cell disorder characterized by a pronounced megakaryocytic hyperplasia in the bone marrow and a striking peripheral thrombocytosis .

• Clinical features
  • Middle aged to elderly, although seen in children and young adults
  • no male/female predilection
  • one third are asymptomatic, discovered only by routine PB examination
  • neither splenomegaly nor hepatomegaly
  • recurrent abortions, fetal growth retardation, thought to be due to placental infarcts

• Diagnostic criteria
  • platelet count > 600 x 10 ^9/L
  • Hgb < 13 g/dl or normal red cell mass
  • Iron in marrow, or no response to iron therapy
  • No Ph1 or evidence of bcr/abl hybrid
  • Collagen fibrosis of marrow
    • Absent
    • Less than 1/3 biopsy without splenomegaly and leukoerythroblastic reaction
  • No demonstrable cause for thrombocytosis

• Peripheral blood findings
  • leukocytosis generally mild; rarely greater then 30 x 10^9
  • mild eosinophilia/basophilia
  • rbc normal unless concurrent iron deficiency; tear drop forms and normoblasts not a feature.
  • thrombocytosis with giant platelets ; bizarre forms
  • increased MPV
  • circulating megakaryocytes and megakaryocytic fragments

• Bone marrow findings
  • mild to moderate hypercellularity
  • striking megakaryocytic hyperplasia with clustering and sheets
  • megakaryocytes enlarged and hyperlobated
  • erythroid and myeloid lines not remarkable
  • mild reticulin fibrosis in a minority of cases

• Most Common Causes of Marrow Infiltration
  • Carcinomatosis
  • Myelofibrosis: primary or secondary
  • Myeloproliferative disorders
  • Lymphoproliferative disorders
  • Lipid storage diseases
  • Infections: TB, fungal

• Other
  • transformations to acute leukemia less than other myeloproliferative disorders
  • median survival 10-15 years, if complications of thromboembolism and hemorrhage controlled