Chronic Myeloproliferative Disorders (MPNs): Causes, Symptoms, Diagnosis and Treatment — Overview, Diagnosis & Treatment Options | MyMedicPlus

Chronic myeloproliferative neoplasms (MPNs) are a group of clonal hematopoietic stem cell disorders characterized by overproduction of mature myeloid cells and a predisposition to thrombosis, bleeding, leukemic transformation, and MF progression. The Philadelphia chromosome-negative MPNs recognized by WHO 2022 include polycythemia vera (PV — excess red blood cell production), essential thrombocythemia (ET — excess platelet production), and primary myelofibrosis (MF — progressive bone marrow fibrosis with extramedullary hematopoiesis). Together they affect approximately 40,000-50,000 people in the US per year. The discovery of JAK2 V617F mutation in 2005 (present in >95% of PV and ~55% of ET and MF) and subsequent CALR and MPL mutations have transformed MPN diagnosis from one of exclusion to a molecularly defined approach. JAK1/2 inhibitors (ruxolitinib, fedratinib, pacritinib, momelotinib) provide effective symptom control and spleen reduction, while allogeneic SCT remains the only curative option for MF.

Acquired somatic mutations in the JAK-STAT signaling pathway are the principal molecular drivers of MPNs. JAK2 V617F (chromosome 9p24, exon 14) is present in >95% of PV and approximately 55% of ET and MF patients, constitutively activating JAK-STAT5, MAPK, and PI3K pathways. JAK2 exon 12 mutations occur in the remaining 5% of PV. CALR (calreticulin) mutations (chromosome 19p13.2) — frameshift insertions/deletions creating a novel C-terminal sequence that activates MPL (thrombopoietin receptor) — are present in approximately 25% of ET and 25-30% of MF. MPL (thrombopoietin receptor) W515K/L mutations occur in approximately 8% of MF and 3% of ET. Triple-negative MPNs (no JAK2, CALR, or MPL mutation) exist and require exclusion of reactive thrombocytosis. Additional somatic mutations in ASXL1, EZH2, IDH1/2, SRSF2, SF3B1, and TP53 confer increased leukemic transformation risk. Risk factors include age (median 65-70 at diagnosis), family history (rare but documented hereditary predisposition), and prior radiation exposure.

Polycythemia vera (PV): aquagenic pruritus (itching after hot water contact — pathognomonic, due to activated basophils and histamine), erythromelalgia (burning pain and redness of the feet and hands from platelet-mediated microvascular occlusion), headaches, visual disturbances, thrombotic events (stroke, deep vein thrombosis, Budd-Chiari syndrome), hypertension, plethoric facial flushing, and splenomegaly. Essential thrombocythemia (ET): may be asymptomatic; presents with thrombosis (arterial: TIA, stroke; venous: DVT/PE) or paradoxically bleeding (acquired von Willebrand syndrome from platelet consumption at very high platelet counts). Myelofibrosis (MF): profound fatigue, massive splenomegaly with associated abdominal fullness, early satiety and weight loss, progressive anemia requiring transfusions, constitutional symptoms (night sweats, fever, weight loss), bone pain from extramedullary hematopoiesis, and leukemic transformation signs (increasing blasts, worsening cytopenias).

WHO 2022 MPN diagnostic criteria integrate clinical, laboratory, and bone marrow histological findings with molecular markers. JAK2, CALR (exon 9 by PCR or NGS), and MPL mutation testing is essential for all suspected MPNs. PV diagnosis: JAK2 V617F or JAK2 exon 12 mutation plus HGB >16.5 g/dL (men) or >16.0 g/dL (women) or hematocrit >49%/48%; bone marrow biopsy shows hypercellularity with trilineage proliferation; serum EPO is subnormal. ET diagnosis: platelet count >450×10⁹/L plus characteristic bone marrow megakaryocytic hyperplasia; exclusion of reactive thrombocytosis and other MPNs. MF diagnosis: bone marrow biopsy showing megakaryocytic proliferation and atypia with reticulin/collagen fibrosis grade MF-1 to MF-3 (WHO). DIPSS and DIPSS-plus scoring stratify MF prognosis and guide transplant candidacy. Additional prognostic mutations (ASXL1, SRSF2, IDH1/2, TP53) by NGS further risk-stratify MF.

Polycythemia vera: phlebotomy to maintain hematocrit below 45% (men) and below 42% (women) — the primary thrombosis prevention intervention; low-dose aspirin 81 mg daily for all patients; hydroxyurea for high-risk patients (age >60 or prior thrombosis) achieving platelet count below 400×10⁹/L; ruxolitinib 10 mg BD for PV inadequately controlled with or intolerant to hydroxyurea (RESPONSE trial: superior hematocrit control and 60% reduction in thromboembolic events versus best available therapy). Essential thrombocythemia: low-dose aspirin for all symptomatic or high-risk patients; hydroxyurea for high-risk ET; anagrelide as second-line for platelet reduction; ruxolitinib for hydroxyurea-refractory ET. Primary myelofibrosis: ruxolitinib 20 mg BD (or 15 mg BD if platelets 100-200×10⁹/L) reduces spleen volume and improves symptoms; fedratinib for ruxolitinib-refractory or intolerant MF; pacritinib for severely cytopenic MF (platelets <50×10⁹/L); momelotinib for anemic MF. Allogeneic SCT: the only potentially curative treatment, recommended for DIPSS-plus intermediate-2 and high-risk MF in eligible patients under age 70. Danazol or luspatercept for MF-related anemia.

Prognosis varies substantially among the three major MPN subtypes. Polycythemia vera (PV): median OS is approximately 14-20 years from diagnosis; most patients maintain near-normal life expectancy if thrombosis, bleeding, and leukemic transformation are prevented through phlebotomy, aspirin, and cytoreductive therapy. Cumulative risk of transformation to myelofibrosis is approximately 10-15% at 10 years and to AML approximately 5-10% at 15 years. Essential thrombocythemia (ET): median OS is approximately 19-20 years, approaching that of the age-matched general population; risk of transformation to MF is approximately 10-15% at 15 years and to AML approximately 3-5% at 15 years. Primary myelofibrosis (MF): the most serious MPN, with median OS dependent on DIPSS-plus prognostic score — low risk: median OS approximately 15 years; intermediate-1: approximately 6-7 years; intermediate-2: approximately 4 years; high-risk: approximately 1.5-2 years. Blast-phase transformation (AML) occurs in approximately 10-20% over 10 years and is associated with very poor prognosis (median OS 2-6 months). Ruxolitinib improves OS in MF (COMFORT-II: hazard ratio 0.48 at 5 years). Allogeneic SCT is the only curative treatment for MF, with 5-year OS approximately 30-50% in eligible patients under age 70 with matched donors. Key adverse prognostic factors for MF include high DIPSS-plus score, ASXL1, SRSF2, IDH1/2, and TP53 mutations, transfusion dependence, and constitutional symptom burden; CALR type 1 mutation is a favorable prognostic factor. Long-term monitoring includes CBC every 3-6 months, bone marrow biopsy every 3-5 years to assess fibrosis progression and exclude blast transformation, and regular assessment of cardiovascular risk factors given the elevated thrombosis risk across all MPN subtypes.

No established preventive measures exist for MPNs — they arise from de novo acquired somatic JAK2, CALR, or MPL mutations without identifiable preventable triggers. However, once MPNs are diagnosed, thrombosis prevention is a critical management priority: phlebotomy in PV to maintain hematocrit below 45%, antiplatelet therapy (aspirin) in high-risk ET and PV, cytoreductive therapy with hydroxyurea or ruxolitinib in high-risk patients — these measures substantially reduce the major morbidity of arterial and venous thrombosis. Cardiovascular risk factor control (hypertension, diabetes, dyslipidemia, smoking cessation) is strongly recommended in all MPN patients to reduce the additive thrombotic risk from both the MPN and conventional cardiovascular risk factors. Avoiding estrogen-containing contraceptives and HRT reduces thrombosis risk in women with PV and ET. JAK2 V617F can be detected in peripheral blood years before overt MPN — the clinical implications of pre-MPN JAK2 V617F screening in general population or family members are under investigation.

Seek hematological evaluation for: persistent erythrocytosis (hemoglobin above 16.5 g/dL in men or 16.0 g/dL in women on repeat testing); persistent unexplained thrombocytosis (platelet count above 450×10⁹/L on two measurements at least 1 month apart, with reactive causes excluded); unexplained splenomegaly on examination or imaging; aquagenic pruritus — itching triggered by hot water in the absence of dermatological explanation; erythromelalgia — burning pain and redness of hands and feet; unexplained thrombotic events in young adults without conventional cardiovascular risk factors (splanchnic vein thrombosis — Budd-Chiari syndrome or portal/hepatic vein thrombosis — is a classic MPN presentation often preceding the MPN diagnosis); or progressive fatigue with constitutional symptoms including drenching night sweats and weight loss in a patient with a known blood count abnormality. Early diagnosis and optimal thrombosis prevention are the keys to minimizing MPN morbidity.