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Polycythemia Vera - Complete BDS 2nd Year Notes

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1. Definition

• The term "polycythemia" means increased red cells (poly = many, cythemia = cells in blood)
• It is the most common of the myeloproliferative neoplasms

Harrison's, 22E: "PV is a clonal hematopoietic stem cell disorder in which phenotypically normal red cells, granulocytes, and platelets accumulate in the absence of a recognizable physiologic stimulus."

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2. Classification - Where Does PV Fit?

• Chronic Myeloid Leukemia (CML) - BCR-ABL positive
• Polycythemia Vera (PV) - JAK2 mutation
• Essential Thrombocythemia (ET) - JAK2/CALR mutation
• Primary Myelofibrosis (PMF) - JAK2/CALR mutation

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3. Epidemiology

• Incidence: ~2.5 per 100,000 persons (increases to >10/100,000 with age)
• Affects all adult age groups; increases with advancing age
• Women under age 50 predominate in sporadic cases
• Familial transmission is infrequent

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4. Etiology and Pathogenesis

The JAK2 V617F Mutation (KEY EXAM POINT)

• >95% of PV patients carry an activating mutation in the JAK2 gene (Janus Kinase 2)
• The mutation is a point mutation: Valine → Phenylalanine at position 617 (V617F)
• Located in the autoinhibitory pseudokinase domain of JAK2
• This causes constitutive (always-on) kinase activation

Normal JAK2 Function:

• Serves as the signal transducer for the erythropoietin receptor and thrombopoietin receptor
• When erythropoietin binds its receptor, JAK2 is activated → phosphorylates downstream STAT proteins → cell proliferation and survival
• JAK2 also acts as an obligate chaperone for erythropoietin/thrombopoietin receptors in the Golgi apparatus

How the Mutation Causes PV:

• Uncontrolled proliferation of erythroid, granulocytic, and megakaryocytic precursors
• Erythropoietin-independent erythroid colony formation
• Increased resistance to apoptosis (via elevated Bcl-XL expression)

Why Is Serum Erythropoietin LOW in PV?

This low EPO is a key diagnostic differentiator!

Other Genetic Notes:

• ~5% of PV patients who lack V617F have a JAK2 exon 12 mutation - clinically similar
• ~60% of PV patients develop loss of heterozygosity on chromosome 9p (uniparental disomy) → homozygosity for JAK2 V617F → higher disease burden
• Non-random cytogenetic changes (deletion 20q, 13q, trisomy 9) occur in up to 30% of untreated patients
• Homozygous JAK2 V617F is associated with: higher WBC count, more splenomegaly, symptomatic pruritus, faster progression to spent-phase fibrosis

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5. Morphology (Histopathology)

Bone Marrow:

• Hypercellular (but some residual fat usually remains)
• Increased red cell progenitors (erythroid hyperplasia)
• Increased granulocytic precursors
• Increased megakaryocytes
• At diagnosis, ~10% show moderate-marked increase in reticulin fibers

Peripheral Blood:

• Elevated hemoglobin, hematocrit, red cell count
• Often: leukocytosis and thrombocytosis of varying degrees
• Basophilia is characteristic (same as CML)
• Abnormally large platelets

Liver:

• Enlarged (hepatomegaly)
• Small foci of extramedullary hematopoiesis

Spleen:

• Mildly enlarged (~250-300 g) due to vascular congestion

Vascular Changes:

• Congestion of many tissues
• Thromboses and infarctions common (heart, spleen, kidneys)
• Hemorrhages in about 1/3 of patients (GI tract, oropharynx, brain)

Late "Spent Phase" (post-PV myelofibrosis):

• Extensive marrow fibrosis replaces hematopoietic cells
• Increased extramedullary hematopoiesis in spleen and liver → prominent splenomegaly/hepatomegaly
• Can transform to Acute Myeloid Leukemia (AML) - ~10% of patients at 20 years

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6. Clinical Features

Due to Increased Red Cell Mass and Hyperviscosity:

Thrombosis (Most Serious Complication):

• Any vessel can be affected
• Most common: cerebral, cardiac, mesenteric vessels
• Budd-Chiari syndrome (hepatic vein thrombosis) - particularly common in young women with PV; PV should always be suspected in a young woman with hepatic vein thrombosis
• Portal vein thrombosis - more common in male PV patients
• JAK2 V617F is the only mutation associated with hepatic vein thrombosis

Bleeding (~1/3 of patients):

• Paradoxically, despite thrombocytosis, patients also BLEED
• Mechanism: Extreme thrombocytosis (>900,000/mL) → absorption and proteolysis of high-molecular-weight von Willebrand multimers by the large platelet mass → acquired von Willebrand disease
• Sites: GI tract, oropharynx, brain
• Also: easy bruising, epistaxis

Distinctive/Pathognomonic Features:

1. Aquagenic pruritus - intense itching after contact with water (hot or cold); due to mast cell activation by JAK2 V617F; may precede diagnosis by years
2. Erythromelalgia - episodic burning pain, warmth, and redness of the hands/feet due to thrombocytosis-induced platelet stickiness; responds to aspirin

Other Features:

• Splenomegaly (present in most patients)
• Hepatomegaly
• Hyperuricemia and gout - due to high cell turnover (breakdown of purines)
• Peptic ulcer disease - due to increased Helicobacter pylori infection incidence in PV
• Constitutional symptoms: fatigue, weight loss (from inflammatory cytokines)
• Hypertension is common

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7. Oral and Dental Relevance (Important for BDS!)

• Always check CBC before invasive procedures
• Consult the patient's hematologist before oral surgery
• Avoid aspirin in patients with extreme thrombocytosis (can worsen bleeding risk)
• Elective surgery should be deferred until hematocrit is controlled (<45%)

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8. Diagnosis

When PV Is Obvious:

When PV Is Subtle (isolated elevated hemoglobin):

1. Relative polycythemia (pseudopolycythemia / Gaisbock's syndrome) - hemoconcentration from dehydration, diuretics, smoking, androgens. Red cell mass is NORMAL, just plasma volume is low.
2. Absolute polycythemia, secondary - EPO elevated (hypoxia, high altitude, tumors like hypernephroma/hepatoma, COPD)
3. Absolute polycythemia, primary = PV - EPO low, JAK2 mutation present

Key Diagnostic Tests:

Note: Red cell mass and plasma volume measurements using radioactive tracers (⁵¹Cr for red cells, ¹²⁵I-albumin for plasma) are the definitive tests for true absolute erythrocytosis but are now largely superseded by JAK2 mutation testing.

WHO 2016 Diagnostic Criteria for PV (High-yield):

1. Hemoglobin >16.5 g/dL (men) or >16 g/dL (women) OR Hematocrit >49% (men) or >48% (women) OR elevated red cell mass
2. Bone marrow biopsy showing trilineage hypercellularity (panmyelosis)
3. JAK2 V617F or JAK2 exon 12 mutation present

• Serum EPO level below normal range

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9. Complications (Natural History)

Short-term:

• Thrombosis (cerebral, cardiac, mesenteric, hepatic, portal)
• Hemorrhage (GI, oropharyngeal, cerebral)
• Erythromelalgia, pruritus, peptic ulcer

Long-term:

• Post-PV Myelofibrosis ("Spent Phase"): ~15% of patients; progressive marrow fibrosis with extramedullary hematopoiesis; transfusion-dependent anemia; massive splenomegaly
• Acute Myeloid Leukemia (AML): Low incidence in untreated patients; increased by chemotherapy/radiation (especially hydroxyurea)
• Transformation to blast crisis is less abrupt than CML

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10. Treatment

Goal: Prevent thrombosis by reducing red cell mass

1. Phlebotomy (First-line):

• Removal of blood (500 mL at a time)
• Rapidly reduces blood volume and viscosity
• Does NOT control leukocytosis or thrombocytosis
• Repeated phlebotomy causes iron deficiency (intentionally, to limit erythropoiesis)
• Can paradoxically cause extreme thrombocytosis → increases thrombotic risk

2. Aspirin (low dose):

• 81 mg/day for most patients
• Prevents thrombosis and treats erythromelalgia
• Caution: Avoid in extreme thrombocytosis (>1,000,000/mL) due to acquired vWD and bleeding risk

3. Myelosuppressive Therapy (for high-risk patients):

• Hydroxyurea (hydroxycarbamide) - most commonly used cytoreductive agent; inhibits ribonucleotide reductase; reduces all cell lines; can cause leukemia long-term
• Ruxolitinib - JAK1/JAK2 inhibitor; used when hydroxyurea fails or is not tolerated; highly effective
• Interferon-alpha - good for young patients and pregnant women; no leukemic risk
• Busulfan, ³²P-phosphorus - older agents, used in elderly

4. Allopurinol:

• To manage hyperuricemia and prevent gout

5. Anticoagulation:

• For patients with thrombotic events

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11. Comparison Table: PV vs Secondary Polycythemia vs Relative Polycythemia

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12. Key Facts Summary for Exams

• PV = myeloproliferative neoplasm, panmyelosis, predominantly red cell increase
• Mutation = JAK2 V617F (>95%); constitutive activation of JAK/STAT pathway
• EPO is LOW (negative feedback from excess red cells)
• Classic symptom: aquagenic pruritus (water-induced itching)
• Classic complication: Hepatic vein thrombosis (Budd-Chiari) in young women
• Both thrombosis AND bleeding can occur
• Peripheral blood: basophilia, thrombocytosis, large platelets
• Treatment: Phlebotomy + low-dose aspirin ± hydroxyurea
• Target Hematocrit: <45% (men), <42% (women)
• Can progress to: post-PV myelofibrosis OR acute myeloid leukemia (AML)
• Low EPO + JAK2 mutation = diagnose PV without bone marrow biopsy

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Recent review note: A 2025 JAMA review (Tremblay et al., PMID 39556352) and a 2024 update by Tefferi & Barbui (PMID 37357958) confirm these fundamentals remain current, with ruxolitinib now firmly established as second-line therapy after hydroxyurea failure.