A bone marrow trephine biopsy from a patient with suspected myeloproliferative neoplasm shows hypercellularity with prominent megakaryocytic proliferation, clustering of pleomorphic megakaryocytes with cloud-like nuclei, and no increase in reticulin fibrosis. JAK2 V617F is detected. Which diagnosis does WHO 5th edition 2022 support?

• A Essential thrombocythemia (ET) — prefibrotic phase
• B Polycythemia vera
• C Myelodysplastic syndrome with excess blasts
• D Primary myelofibrosis, prefibrotic/early stage (prePMF) ✓

Explanation

WHO 2022 emphasizes distinguishing prefibrotic primary myelofibrosis (prePMF) from essential thrombocythemia, as they can both present without significant fibrosis and with elevated platelet counts. The key morphological discriminator is megakaryocyte morphology: prePMF shows clustered megakaryocytes with atypical, hyperchromatic, cloud-like (bulbous) nuclei and dense chromatin, whereas ET megakaryocytes are large, mature, with staghorn (hyperlobulated) nuclei. prePMF carries a worse prognosis than ET, with higher rate of transformation to overt fibrosis and reduced overall survival. JAK2 V617F is present in both but does not discriminate.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.