Polycythemia Vera
A slow-growing blood cancer causing the bone marrow to make too many red blood cells, making the blood dangerously thick and prone to clotting.
Emergency Management: Acute thrombotic events (CVA, STEMI, massive PE). Severe extreme hyperviscosity syndrome requiring emergent therapeutic erythrocytapheresis (automated removal of RBCs with plasma replacement).
Polycythemia Vera (PV) is a chronic Philadelphia chromosome-negative myeloproliferative neoplasm (MPN) characterized by the clonal proliferation of a multipotent bone marrow stem cell. It results in a primary overproduction of red blood cells (erythrocytosis) independently of the hormone erythropoietin, typically accompanied by elevated white blood cells (leukocytosis) and platelets (thrombocytosis).
Detailed Overview
The disease is almost universally driven by a somatic mutation in the JAK2 gene (JAK2 V617F). This mutation causes the hematopoietic stem cells to become hypersensitive to or independent of growth factors like erythropoietin. The massively increased red blood cell mass drastically increases blood viscosity, leading to sluggish blood flow, tissue hypoxia, and a profound risk of arterial and venous thromboses (stroke, myocardial infarction, DVT, Budd-Chiari syndrome). Over time, the hyperactive bone marrow can 'burn out,' transforming into myelofibrosis, or rarely, acute myeloid leukemia (AML).
Epidemiology & Demographics
Incidence is 1-2 per 100,000 annually. Prevalence is approximately 22 per 100,000. Median age at diagnosis is 60 years. Slightly more common in men.
Etiological Mechanism
An acquired genetic disorder. Over 95% of patients carry the JAK2 V617F mutation in exon 14. An additional 3-4% have mutations in JAK2 exon 12. Familial cases are extremely rare.
Primary Causes
Clonal stem cell mutation activating the JAK-STAT signaling pathway, driving unchecked myelopoiesis.
The JAK2 tyrosine kinase is normally coupled to the erythropoietin (EPO) receptor. When EPO binds, JAK2 phosphorylates STAT proteins to signal RBC production. The JAK2 V617F mutation causes the kinase to be constitutively active, constantly signaling the marrow to produce erythrocytes, leukocytes, and megakaryocytes even in the complete absence of EPO. The resulting polycythemia hyperviscosity leads to high shear stress on endothelial cells, activating platelets and promoting thrombosis. Increased cell turnover leads to hyperuricemia, and increased histamine release from basophils causes profound itching.
Diagnostic Criteria & Guidelines
WHO 2016 Criteria require all 3 major, or first 2 major + 1 minor. Major: 1) Hemoglobin >16.5 g/dL (men) or >16.0 g/dL (women), OR Hematocrit >49% (men) or >48% (women). 2) Bone marrow biopsy showing hypercellularity with panmyelosis. 3) Presence of JAK2 V617F or JAK2 exon 12 mutation. Minor: Subnormal serum erythropoietin (EPO) level.
The cornerstone for ALL patients is therapeutic phlebotomy (blood-letting) to maintain Hematocrit strictly <45%, and low-dose Aspirin (81-100 mg/day) to prevent thrombosis. In high-risk patients (age >60 or history of thrombosis), cytoreductive therapy with Hydroxyurea (500-1000 mg/day PO) is first-line to lower blood counts.
Second-Line & Adjunctive Therapy
For younger patients requiring cytoreduction or those intolerant to hydroxyurea: Pegylated Interferon alfa-2a (Pegasys). For patients refractory to hydroxyurea with severe pruritus or splenomegaly: Ruxolitinib (JAK1/2 inhibitor, 10-20 mg PO BID).
Surgical & Procedural Management
Rarely, splenectomy for massive, painful, refractory splenomegaly in the spent phase.
Patient Counseling & Advice
Educate the patient that PV is a chronic, lifelong blood cancer, but it is manageable. Explain that the goal of taking their blood (phlebotomy) is to make them iron deficient, which slows down the bone marrow. Emphasize the critical importance of taking daily aspirin and keeping appointments to check hematocrit to prevent fatal blood clots.
Follow-Up & Monitoring Schedule
Check CBC every 2-4 weeks until Hematocrit is stabilized <45%. Once stable, monitor CBC every 3 months. Monitor for symptoms of disease progression (increasing spleen size, massive weight loss, severe night sweats).
Preventive Strategies
No prevention available. Focus is on preventing thrombotic complications.
With strict control of hematocrit, median survival approaches 20 years, slightly less than the age-matched general population. The primary risk to life is a thrombotic event or transformation to AML.