Essential Thrombocythemia
Definition
- Chronic myeloproliferative neoplasm involving primarily the megakaryocytic lineage
Diagnostic Criteria
- All of the following are required
- Must not meet criteria for CML, PMF, PV, MDS or other myeloid neoplasm (see Differential Diagnosis)
- Always check for BCR-ABL1
- Rare p230 isoform of CML can present with thrombocytosis
- MDS syndromes with thrombocytosis such as RARS-T and 5q- can have JAK5V617F mutations
- Always check for BCR-ABL1
- Sustained platelet elevation ≥450 x 103/μL
- Bone marrow biopsy with megakaryocytic hyperplasia
- Enlarged, mature megakaryocytes
- No significant hyperplasia or left shift of granulocytic or erythroid lineages
- JAK2V617F (present in about 50%) or other clonal marker
- If no clonal marker, exclude reactive thrombocytosis (see Differential Diagnosis)
- Must not meet criteria for CML, PMF, PV, MDS or other myeloid neoplasm (see Differential Diagnosis)
- Peripheral blood thrombocytosis
- Markedly elevated platelets with giant platelets
- Normal or mildly elevated WBC
- RBC normal or show effects due to hemorrhage
- May be hypochromic/microcytic
- No increase in hemoglobin or hematocrit to polycythemia range when iron replete
- No significant teardrop population
- No granulocyte dysplasia
- Bone marrow shows megakaryocytic hyperplasia
- Overall normocellular or moderately hypercellular
- Megakaryocytes dispersed or loosely clustered throughout the marrow
- Large to giant mature megakaryocytes
- Abundant cytoplasm
- Deeply lobulated nuclei (staghorn-like)
- Not hyperchromatic and clustered (as in cellular phase primary myelofibrosis)
- Not monolobated or multinucleated (as in MDS)
- Minimal fibrosis (MF-0 or 1 in European Consensus System, Thiele 2005)
- No dense reticulin fibrosis or collagen fibrosis
- Typically no erythroid or granulocytic hyperplasia
- Secondary erythroid hyperplasia may ocurr post hemorrhage
- No erythroid dysplasia or ring sideroblasts
- No granulocytic dysplasia or increased blasts
- Rare progression to post-ET marrow fibrosis
- Approximately 2%
Dita Gratzinger MD PhD
Tracy I George MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342
Original posting: 10/23/11
