Essential Thrombocythemia

Essential thrombocythemia (ET) is a chronic myeloproliferative neoplasm characterized by clonal megakaryocyte proliferation in the bone marrow, resulting in sustained platelet elevation (>450,000/mcL). Three driver mutations account for ~90% of ET cases: (1) JAK2 V617F mutation (~60%): causes constitutive activation of the JAK-STAT signaling pathway, driving megakaryocyte proliferation independent of thrombopoietin (TPO) stimulation; (2) CALR (calreticulin) mutation (~25%): activates the MPL (thrombopoietin receptor) pathway through an alternative mechanism; (3) MPL mutation (~5%): directly activates the thrombopoietin receptor. The remaining ~10% are 'triple-negative' (no detectable driver mutation). ET has a paradoxical dual risk: THROMBOTIC complications (stroke, TIA, MI, DVT, PE, digital ischemia, erythromelalgia, portal/splenic vein thrombosis) from excessive platelet activation and aggregation, AND HEMORRHAGIC complications (especially at very high platelet counts >1,000,000/mcL) from acquired von Willebrand disease (excessive platelets absorb and degrade large VWF multimers, impairing primary hemostasis). Risk stratification guides therapy: the IPSET-thrombosis score classifies patients as very low, low, intermediate, or high risk based on age (≥60), JAK2 mutation status, and history of thrombosis. The nurse monitors CBC with platelet count trends, assesses for thrombotic symptoms (headache, visual changes,...