C h r o n i c M y e l o p r o l i f e r a t i v e D i s o r d e r s
General
• ET is a rare myeloproliferative disorder in which the primary manifestation is
a very high platelet count.
• Criteria for diagnosis (PV Study Group):
• Platelet count must be >600,000 (normal = 150,000 - 450,000)
• RBC mass must not be elevated (excludes PV)
• Ph chromosome must be absent (excludes CML)
• Marrow must lack fibrosis (excludes chronic myelofibrosis)
• All other causes of thrombocytosis (e.g., iron deficiency anemia, cancer)
must be excluded
Clinical Features
Age
• Usually occurs in people >50, but occasionally occurs in young women
Symptoms
• Hemorrhagic phenomena (GI bleeding)
• Thrombotic phenomena (MI, deep venous thrombosis, stroke)
Signs
• Purpura, ecchymoses
• Pallor, tachycardia (anemia)
• Splenomegaly (mild)
Morphology
Blood
• Sustained, marked increase in platelet count (usually >1,000,000)
• Platelets usually look abnormal (large and/or hypogranular)
Bone marrow
• Normal to increased cellularity
• Lots of megakaryocytes ("back-to-back")
Laboratory Findings
• Platelet count markedly elevated
• Microcytic, hypochromic anemia frequently present (from bleeding)
• WBC mildly elevated
Treatment and Prognosis
• Main aim of treatment is to reduce chances of hemorrhage or thrombosis.
Do this by lowering platelet count (use platelet pheresis or chemotherapy),
or by decreasing platelet aggregation of platelets (aspirin).
• Most patients survive at least 5-8 years.
• Death (when from ET itself) from hemorrhage, thrombosis, or - rarely -
leukemic transformation.
