Diagnostic criteria for essential thromocythemia (ET) and post-ET myelofibrosis (post-ET MF)
| ET . | Post-ET MF . |
|---|---|
| Major criteria 1. Platelet count ≥ 450 × 109/L 2. Bone marrow biopsy showing proliferation mainly of the megakaryocytic lineage, with increased numbers of enlarged, mature megakaryocytes with hyperlobulated staghorn-like nuclei, infrequently dense clusters*; no significant increase or left shift in neutrophil granulopoiesis or erythropoiesis; no relevant BM fibrosis† 3. Diagnostic criteria for BCR::ABL1-positive CML, PV, PMF, or other myeloid neoplasms are not met 4. JAK2, CALR, or MPL mutation‡ Minor criteria • Presence of a clonal marker§ or absence of evidence of reactive thrombocytosisǁ | Required criteria 1. Previous established diagnosis of ET 2. Bone marrow fibrosis of grade 2 or 3 Additional criteria 1. Anemia (ie, below the reference range given age, sex, and altitude considerations) and a >2 g/dL decrease from baseline hemoglobin concentration 2. Leukoerythroblastosis 3. Increase in palpable splenomegaly of >5 cm from baseline or the development of a newly palpable splenomegaly 4. Elevated LDH level above the reference range 5. Development of any 2 (or all 3) of the following constitutional symptoms: >10% weight loss in 6 mo, night sweats, unexplained fever (>37.5°C) |
| The diagnosis of ET requires either all major criteria or the first 3 major criteria plus the minor criteria | The diagnosis of post-ET MF is established by all required criteria and at least 2 additional criteria |
| ET . | Post-ET MF . |
|---|---|
| Major criteria 1. Platelet count ≥ 450 × 109/L 2. Bone marrow biopsy showing proliferation mainly of the megakaryocytic lineage, with increased numbers of enlarged, mature megakaryocytes with hyperlobulated staghorn-like nuclei, infrequently dense clusters*; no significant increase or left shift in neutrophil granulopoiesis or erythropoiesis; no relevant BM fibrosis† 3. Diagnostic criteria for BCR::ABL1-positive CML, PV, PMF, or other myeloid neoplasms are not met 4. JAK2, CALR, or MPL mutation‡ Minor criteria • Presence of a clonal marker§ or absence of evidence of reactive thrombocytosisǁ | Required criteria 1. Previous established diagnosis of ET 2. Bone marrow fibrosis of grade 2 or 3 Additional criteria 1. Anemia (ie, below the reference range given age, sex, and altitude considerations) and a >2 g/dL decrease from baseline hemoglobin concentration 2. Leukoerythroblastosis 3. Increase in palpable splenomegaly of >5 cm from baseline or the development of a newly palpable splenomegaly 4. Elevated LDH level above the reference range 5. Development of any 2 (or all 3) of the following constitutional symptoms: >10% weight loss in 6 mo, night sweats, unexplained fever (>37.5°C) |
| The diagnosis of ET requires either all major criteria or the first 3 major criteria plus the minor criteria | The diagnosis of post-ET MF is established by all required criteria and at least 2 additional criteria |
Three or more megakaryocytes lying adjacent without other BM cells in between; in most of these rare clusters ≤ 6 megakaryocytes may be observed, increase in huge clusters (>6 cells) accompanied by granulocytic proliferation is a morphological hallmark of pre-PMF (Table 5).
Very rarely a minor increase in reticulin fibers may occur at initial diagnosis (grade 1).
It is recommended to use highly sensitive assays for JAK2 V617F (sensitivity level < 1%) and CALR and MPL (sensitivity level 1% to 3%); in negative cases, consider a search for noncanonical JAK2 and MPL mutations.
Assessed by cytogenetics or sensitive NGS techniques.
Reactive causes of thrombocytosis include a variety of underlying conditions like iron deficiency, chronic infection, chronic inflammatory disease, medication, neoplasia, or history of splenectomy.