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

Chronic myeloproliferative neoplasms (MPNs) are clonal hematopoietic stem cell disorders characterized by excessive proliferation of one or more terminally differentiated myeloid cell lineages in the absence of a reactive cause. The three classical Philadelphia chromosome-negative MPNs are: polycythemia vera (PV) — erythrocytosis with high risk of thrombosis and hemorrhage; essential thrombocythemia (ET) — thrombocytosis with thrombotic and hemorrhagic complications; and primary myelofibrosis (PMF) — fibrotic replacement of bone marrow leading to cytopenias, splenomegaly, and progressive disability. A fourth entity, chronic myeloid leukemia (CML) — a Philadelphia chromosome-positive MPN — is pathobiologically distinct (BCR-ABL1 driven) and managed separately with TKIs. The landmark discovery of the JAK2 V617F somatic mutation in 2005 revolutionized MPN diagnosis: present in >95% of PV, ~50–60% of ET, and ~50–60% of PMF. Additional driver mutations include CALR (calreticulin) mutations in JAK2-negative ET and PMF (~20–30%), and MPL W515L/K mutations (~5%). MPNs have variable prognosis — ET has near-normal life expectancy; MF has median survival of 3–5 years (DIPSS intermediate-2 and high risk) to >15 years (low risk). All three classical MPNs carry risk of transformation to AML (highest in MF, ~15–20% at 10 years).

Classical MPNs arise from clonal expansion of a multipotent hematopoietic stem cell acquiring a driver mutation that constitutively activates JAK-STAT signaling. JAK2 V617F (a point mutation in the pseudokinase domain of JAK2 causing constitutive JAK2 activation) is the dominant driver in PV (>95%), ET (~55%), and PMF (~55%). In JAK2-negative ET and MF, CALR exon 9 mutations (type 1: 52-bp deletion; type 2: 5-bp insertion) activate MPL signaling, driving thrombopoiesis. MPL mutations activate thrombopoietin receptor signaling directly. A small proportion of ET and MF are 'triple negative' — lacking JAK2, CALR, and MPL mutations. Additional somatic mutations in ASXL1, DNMT3A, TET2, EZH2, IDH1/2, and SRSF2 modify the disease phenotype and confer adverse prognosis. Risk factors for MPN development include: advanced age (peak incidence 50–70 years), male sex (PV and MF), exposure to ionizing radiation and petroleum products (modest association), and familial MPN — germline predisposition including 46/1 haplotype of JAK2 ('GGCC' haplotype) and constitutional mutations in SH2B3, RBBP6, and germline CALR/MPL.

Polycythemia vera: symptoms of hyperviscosity and thrombosis predominate. Classic triad: pruritus (aquagenic pruritus — intense itching after warm water contact, from mast cell histamine release — pathognomonic of PV), plethoric facial appearance, and splenomegaly. Symptoms also include headache, dizziness, visual disturbances, tinnitus, and erythromelalgia (burning pain and erythema of hands and feet from platelet-mediated small vessel occlusion). Thrombosis (arterial and venous, including splanchnic vein thrombosis — Budd-Chiari syndrome) is the leading cause of morbidity. Essential thrombocythemia: many patients are asymptomatic at diagnosis. Thrombotic events (stroke, TIA, DVT, PE, MI) occur in 15–25% at diagnosis or within 10 years. Microvascular symptoms from platelet-mediated arteriolar occlusion: erythromelalgia, headache, and visual scotomata. Hemorrhage (paradoxically from acquired von Willebrand syndrome at very high platelet counts >1500×10⁹/L). Myelofibrosis: constitutional symptoms (profound fatigue, night sweats, weight loss, fever) are dominant and severely impair quality of life. Massive splenomegaly causes early satiety, left upper quadrant pain, and portal hypertension. Cytopenias from marrow failure cause anaemia-related fatigue and thrombocytopenic bleeding. Bone pain from extramedullary haematopoiesis and portal hypertension are advanced features.

Diagnosis requires integration of clinical, morphological, and molecular findings per the 2022 WHO Classification. PV diagnosis: haemoglobin >16.5g/dL (males) or >16g/dL (females), or haematocrit >49%/48%, plus bone marrow showing panmyelosis with pleomorphic megakaryocytes, and JAK2 V617F or JAK2 exon 12 mutation (mandatory). Subnormal serum EPO supports PV vs secondary erythrocytosis. ET diagnosis: sustained platelet count >450×10⁹/L, characteristic megakaryocyte morphology (large, hyperlobulated, 'staghorn' nuclei), JAK2/CALR/MPL mutation or in absence of triple negativity — exclusion of reactive thrombocytosis, PV, MF, MDS, CML. MF diagnosis (prefibrotic or overt) requires bone marrow trephine biopsy with Gömöri silver stain for reticulin fibrosis grading (MF grade 0–3). Molecular testing: JAK2 V617F allele burden by quantitative PCR; CALR and MPL by PCR/NGS; additional mutation panel (ASXL1, EZH2, IDH1/2, SRSF2 — the 'HMR' high-molecular-risk mutations) for MF prognostication. Prognosis in MF: DIPSS (dynamic IPSS) and MIPSS70+ (incorporating cytogenetics and molecular risk) stratify patients for allogeneic SCT decision-making.

PV treatment: Phlebotomy to target haematocrit <45% (males) and <42% (females) is the cornerstone — ECLAP trial confirmed haematocrit >45% doubles thrombosis risk. Low-dose aspirin 100 mg/day reduces thrombotic events (ECLAP trial). Cytoreduction with hydroxyurea (starting 500–1000 mg/day, titrated) for high-risk patients (age >60 or prior thrombosis). Interferon-alpha (ropeginterferon alfa-2b, pegylated) is an alternative for younger patients (molecular remission achievable), avoiding teratogenicity concerns and leukemogenicity of hydroxyurea. Ruxolitinib (JAK1/2 inhibitor, 10 mg BID) is reserved for hydroxyurea-refractory/intolerant PV. ET treatment: Low-risk ET (age <60, no thrombosis, no cardiovascular risk factors): low-dose aspirin only. High-risk ET (age ≥60 or prior thrombosis): aspirin + cytoreduction with hydroxyurea (first-line) or anagrelide (second-line; preferred in young patients due to no leukemogenicity). MF treatment: Ruxolitinib (20 mg BID for platelet count ≥200×10⁹/L) is first-line for intermediate-2 and high-risk MF — COMFORT-I/II trials demonstrated significant spleen volume reduction and symptom improvement vs placebo and best available therapy. Fedratinib (JAK2 inhibitor) is second-line after ruxolitinib failure. Pacritinib and momelotinib are approved for MF with thrombocytopenia. Allogeneic SCT is the only potentially curative treatment for MF, recommended for intermediate-2 and high-risk patients under 70 with a suitable donor — 5-year OS of 30–60% depending on risk and conditioning. Luspatercept treats anaemia in MF (PACE-MF trial).

Prognosis among the three classical MPNs varies substantially. Essential thrombocythemia has the most favorable prognosis, with near-normal life expectancy in most patients. Median survival exceeds 20 years, and disease-related mortality — from thrombosis, hemorrhage, or transformation to myelofibrosis or AML — is relatively low with appropriate risk stratification and cytoreductive treatment. Polycythemia vera has a median survival of 14–18 years from diagnosis with modern treatment (phlebotomy, aspirin, hydroxyurea or interferon). The major risks are thrombosis (leading cause of morbidity and death in PV), secondary myelofibrosis (occurring in 10–20% at 20 years), and AML transformation (5–10% at 20 years). Primary myelofibrosis has the worst prognosis of the three: median survival for intermediate-2 risk patients (DIPSS) is approximately 2–4 years; high-risk patients have median survival under 2 years; low-risk patients have median survival exceeding 15 years. The IPSS/DIPSS-plus incorporating age, haemoglobin, leukocyte count, constitutional symptoms, blast count, cytogenetics, and transfusion need guides allogeneic SCT decision-making. Transformation to AML (blastic phase) occurs in approximately 20% of PMF patients at 10 years and carries a dismal prognosis — median survival 3–5 months even with AML-directed treatment. Ruxolitinib significantly improves constitutional symptoms and spleen volume reduction in MF but does not prevent disease transformation or markedly improve overall survival in randomized trials. Allogeneic SCT remains the only potentially curative treatment, with 5-year OS of 30–60% in appropriately selected intermediate-2 and high-risk MF patients.

No preventive strategies exist for development of MPNs. Thrombosis prevention is the primary management goal for PV and ET. All patients should be risk-stratified: low-dose aspirin for all symptomatic patients (unless contraindicated); cardiovascular risk factor control — hypertension, diabetes, smoking cessation, dyslipidaemia management — significantly modifies thrombotic risk in MPN. Phlebotomy adherence in PV is the most critical ongoing intervention. Avoidance of erythropoiesis-stimulating agents in undiagnosed erythrocytosis pending diagnostic workup prevents masking of PV. Monitoring for disease transformation: annual CBC, peripheral blood film, and serum LDH; bone marrow biopsy every 3–5 years or when there is clinical change (unexplained splenomegaly, cytopenias, constitutional symptoms). JAK2 V617F allele burden monitoring may predict transformation risk in PV. Hydroxyurea-treated patients require skin cancer surveillance (hydroxyurea is associated with squamous cell carcinoma of skin with prolonged use).

Seek urgent haematology review for: platelet count persistently above 1000×10⁹/L (extreme thrombocytosis risks both thrombosis and acquired von Willebrand-type hemorrhage); erythrocytosis with haematocrit >54% (high viscosity thrombosis risk); new onset Budd-Chiari syndrome or portal/mesenteric vein thrombosis — these are the classical presentations of an unrecognized underlying PV or ET, and JAK2 V617F testing should be performed in all cases of unexplained splanchnic thrombosis. Any MPN patient developing rapid spleen enlargement, significant constitutional symptoms (fever, night sweats, weight loss), new cytopenias, or rising blast count must be assessed urgently for accelerated phase or blast transformation. Erythromelalgia (burning pain and erythema of extremities) in an ET patient with high platelet count is treated urgently with aspirin — it reflects platelet-mediated arteriolar occlusion and responds dramatically within hours to aspirin.