Polycythaemia Vera

1. Clinical Overview

Polycythaemia Vera (PV) is a Philadelphia chromosome-negative myeloproliferative neoplasm (MPN) characterised by clonal proliferation of multipotent haematopoietic stem cells, leading to increased red cell mass (true erythrocytosis) with frequent concurrent leukocytosis and thrombocytosis. [1,2]

PV represents the most common cause of primary erythrocytosis and is distinguished from secondary causes by the presence of the JAK2 V617F mutation in > 95% of cases. [1] The remaining cases harbour mutations in JAK2 exon 12, making PV effectively a JAK2-driven malignancy. [3]

The disease carries significant morbidity and mortality primarily from thrombotic complications, which represent the leading cause of death and can occur early in the disease course, even before diagnosis. [4] Long-term risks include transformation to myelofibrosis (MF) in approximately 15% of patients at 15 years, and progression to acute myeloid leukaemia (AML) in 5-10% over the patient's lifetime. [5]

Clinical Significance

With modern treatment strategies—principally therapeutic venesection targeting haematocrit less than 0.45, low-dose aspirin, and cytoreductive therapy in high-risk patients—median survival exceeds 15-20 years. [6,7] The landmark CYTO-PV trial demonstrated that strict haematocrit control (less than 0.45) reduces cardiovascular death and major thrombosis by 59% compared to a target of 0.45-0.50. [7]

Clinical Pearls

The "Ruddy Complexion": Patients classically present with a plethoric (red) face, conjunctival suffusion, and engorged retinal veins on fundoscopy—physical signs reflecting increased red cell mass and hyperviscosity. [8]

Aquagenic Pruritus: Intense itching triggered by contact with water (especially warm baths/showers) occurs in 40-70% of patients and may precede diagnosis by years. It results from histamine and cytokine release from activated basophils and mast cells, and is highly specific for MPNs. [9]

Budd-Chiari Syndrome: PV is the single most common cause of hepatic vein thrombosis (accounting for ~40% of cases). Any young patient presenting with Budd-Chiari should be screened for JAK2 mutations. [10]

Erythromelalgia: Burning pain in the hands and feet with warmth and erythema, often precipitated by heat. This microvascular occlusion syndrome is pathognomonic of MPNs and responds dramatically to low-dose aspirin. [9]

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2. Epidemiology

Incidence and Prevalence

PV is the most common MPN, accounting for approximately 45% of all MPNs. [1]

Demographics

• Sex: Slight male predominance (male:female ratio 1.2-1.8:1). [11]
• Ethnicity: More common in Caucasians (especially Ashkenazi Jews) compared to African or Asian populations. [11]
• Familial clustering: First-degree relatives have a 5-7 fold increased risk, suggesting genetic predisposition despite the acquired nature of JAK2 mutations. [12]

Temporal Trends

Incidence appears stable over recent decades, but earlier diagnosis has increased due to:

• Routine full blood count (FBC) screening
• Widespread availability of JAK2 mutation testing (introduced 2005)
• Revised WHO 2016 diagnostic criteria with lower haemoglobin thresholds. [3]

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3. Aetiology and Pathophysiology

Molecular Pathogenesis

JAK2 V617F Mutation (Exon 14)

Prevalence: Present in 96-97% of PV patients. [1,3]

Mechanism:

1. A somatic point mutation (c.1849G>T) in the JAK2 gene on chromosome 9p24 results in substitution of valine to phenylalanine at position 617 (V617F).
2. This mutation occurs in the JH2 pseudokinase domain, which normally acts as an auto-inhibitory domain regulating the JH1 kinase domain.
3. Loss of auto-inhibition → constitutive activation of JAK2 tyrosine kinase activity, independent of upstream cytokine receptor stimulation.
4. Hypersensitivity to erythropoietin (EPO): Erythroid progenitors proliferate even at low or absent EPO levels (hence serum EPO is typically low/normal in PV). [1,3]

Exam Detail: #### Downstream Signalling Cascade

JAK2 V617F leads to:

• Phosphorylation of STAT5, STAT3, and STAT1 → nuclear translocation → transcription of proliferation and anti-apoptotic genes (BCL-XL, MCL-1).
• Activation of PI3K/AKT/mTOR pathway → enhanced cell survival.
• Activation of MAPK/ERK pathway → increased proliferation.

Zygosity:

• JAK2 V617F homozygosity (30-40% of PV patients) results from acquired uniparental disomy (copy-neutral loss of heterozygosity at 9p).
• Homozygous patients have:
  • Higher WCC and haematocrit
  • Greater splenomegaly
  • Increased risk of progression to myelofibrosis
  • Higher JAK2 V617F variant allele frequency (VAF > 50%). [13]

JAK2 Exon 12 Mutations

Prevalence: 3-4% of PV patients (found in ~50% of JAK2 V617F-negative PV cases). [3]

Characteristics:

• Multiple different mutations identified (most common: p.N542-E543del, p.K539L).
• Occur in the JH2 domain (exon 12), similar functional effect to V617F.
• Phenotype: Isolated erythrocytosis without leukocytosis/thrombocytosis; younger age at diagnosis; lower EPO levels.
• Normal bone marrow or erythroid-predominant hyperplasia (less panmyelosis). [3]

Cellular Pathophysiology

1. Clonal Expansion: A single mutant haematopoietic stem cell (HSC) undergoes clonal expansion.
2. Trilineage Hyperplasia: Although erythroid lineage is most prominent, granulocytic and megakaryocytic lineages are also affected → panmyelosis.
3. Hyperviscosity: Increased red cell mass → elevated haematocrit → increased blood viscosity → sluggish flow, microvascular stasis.
4. Thrombotic Tendency:
   • Hyperviscosity
   • Elevated platelet count and qualitative platelet defects
   • Leukocyte activation → endothelial damage
   • Pro-inflammatory cytokine milieu (IL-1β, TNF-α). [4]
5. Paradoxical Bleeding Risk:
   • Extreme thrombocytosis (> 1000-1500 × 10⁹/L) → acquired von Willebrand disease (consumption of large vWF multimers by excess platelets). [14]

Disease Evolution

Exam Detail: #### Progression Pathways

Spent Phase / Post-PV Myelofibrosis:

• Occurs in 15% of patients by 15 years. [5]
• Progressive marrow fibrosis → extramedullary haematopoiesis → massive splenomegaly.
• Transition from proliferative to fibrotic phase with cytopenias (especially anaemia).
• Increased JAK2 VAF and acquisition of additional mutations (e.g., ASXL1, IDH1/2, SRSF2).

Blast Transformation (Acute Myeloid Leukaemia):

• Cumulative incidence: 5-10% at 20 years. [5]
• Risk increased by prior alkylating agents (e.g., busulfan, chlorambucil) and radioactive phosphorus (³²P) (historic treatments now avoided).
• Hydroxyurea: controversial but likely does not increase leukaemic transformation risk. [15]
• Poor prognosis: median survival post-transformation less than 6 months.

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4. Clinical Presentation

Modes of Presentation

Symptoms

Hyperviscosity Symptoms

• Headache (most common)
• Dizziness, vertigo, tinnitus
• Visual disturbances: Blurred vision, scotomas, amaurosis fugax
• Paraesthesias (digital)
• Cognitive impairment: Concentration difficulty, mental "fog"

Microvascular Symptoms

• Aquagenic pruritus: Intense, unbearable itching after warm water contact (shower, bath, swimming); lasts 30-60 minutes. [9]
• Erythromelalgia: Burning pain in hands/feet with erythema and warmth; relieved by cooling, aspirin.

Systemic Symptoms

• Fatigue, malaise (cytokine-mediated)
• Night sweats, low-grade fever (in 10-15%)
• Weight loss (usually mild)
• Arthralgia/Gout: Due to hyperuricaemia from increased cell turnover (20% of patients). [8]

Vascular Symptoms

• Symptoms of thrombosis: Stroke/TIA, angina/MI, DVT/PE, Budd-Chiari (abdominal pain, ascites).
• Bleeding: Epistaxis, easy bruising, GI bleeding (especially if platelets > 1500 × 10⁹/L). [14]

Signs

General Inspection

• Plethora: Ruddy, dusky-red complexion; "congested" appearance.
• Facial flushing, conjunctival injection, engorged retinal veins.
• Cyanotic tinge to lips and ears (pseudocyanosis).

Abdominal Examination

• Splenomegaly: Palpable in 70-80% of patients; usually mild (2-5 cm below costal margin).
  • Massive splenomegaly suggests progression to myelofibrosis.
• Hepatomegaly: Present in ~40% (extramedullary haematopoiesis).

Cardiovascular

• Hypertension: Present in 30-50% (both cause and consequence of PV). [8]
• Signs of thrombotic disease: Hemiparesis (stroke), absent pulses (arterial occlusion).

Dermatological

• Erythema of palms/soles (erythromelalgia when symptomatic).
• Excoriation marks from scratching (aquagenic pruritus).
• Leg ulcers (uncommon; more frequent with hydroxyurea use).

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5. Differential Diagnosis

Causes of Erythrocytosis

Exam Detail: | Condition | JAK2 V617F | EPO Level | Key Distinguishing Features | |-----------|------------|-----------|----------------------------| | Polycythaemia Vera | Positive (> 95%) | Low/Normal | Panmyelosis; splenomegaly; aquagenic pruritus | | JAK2 Exon 12 PV | Negative | Very low | Isolated erythrocytosis; younger age; normal WCC/Plt | | Secondary Polycythaemia (Hypoxic) | Negative | High | Chronic hypoxia: COPD, sleep apnoea, high altitude, cyanotic heart disease | | Secondary Polycythaemia (EPO-secreting tumours) | Negative | High | Renal cell carcinoma, hepatocellular carcinoma, cerebellar haemangioblastoma, uterine fibroids | | Relative/Apparent Polycythaemia | Negative | Normal | Normal red cell mass, reduced plasma volume; Gaisböck syndrome (obese, hypertensive, smoker) | | High-affinity Haemoglobin | Negative | Normal/High | Familial; onset in childhood/adolescence; positive family history | | Chuvash Polycythaemia | Negative | High | Autosomal recessive; VHL gene mutation; endemic in Chuvash population |

Differentiation from Other MPNs

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6. Investigations

First-Line Investigations

Full Blood Count (FBC)

Diagnostic Thresholds (WHO 2016): [3]

• Haemoglobin:
  • "Males: > 165 g/L (16.5 g/dL)"
  • "Females: > 160 g/L (16.0 g/dL)"
• Haematocrit:
  • "Males: > 0.49"
  • "Females: > 0.48"

Typical Findings:

• Elevated Hb/Hct: Primary abnormality.
• Elevated WCC: Leukocytosis in 60-70% (typically 12-20 × 10⁹/L).
  • Neutrophilia with left shift (myelocytes, metamyelocytes may be present).
  • Basophilia (common in MPNs).
• Elevated Platelets: Thrombocytosis in 50-60% (usually 450-800 × 10⁹/L).
  • Panmyelosis (all three cell lines elevated) strongly suggests PV.

JAK2 Mutation Testing

JAK2 V617F:

• Sensitivity > 95% for PV. [1,3]
• Positive result + elevated Hb/Hct = virtually diagnostic of PV.
• Quantitative assay (qPCR) provides variant allele frequency (VAF):
  • less than 50% = heterozygous
  • ≥50% = homozygous (acquired copy-neutral LOH at 9p)
  • Higher VAF associated with greater thrombotic risk and higher likelihood of progression to MF. [13]

JAK2 Exon 12:

• Test if V617F is negative but PV still suspected (isolated erythrocytosis, low EPO, bone marrow erythroid hyperplasia).
• Positive in ~3-4% of PV patients overall, ~50% of JAK2 V617F-negative PV. [3]

Serum Erythropoietin (EPO)

• Low or inappropriately normal in > 90% of PV patients. [1]
• Distinguishes PV from secondary polycythaemia (where EPO is elevated).
• Caveat: EPO may be normal in ~10% of PV patients, so not absolutely diagnostic.

Second-Line Investigations

Bone Marrow Aspirate and Trephine Biopsy

Not always required if JAK2 V617F positive + elevated Hb/Hct + low EPO. [3]

Indications:

• JAK2 V617F negative cases (to confirm diagnosis and exclude other causes).
• Atypical presentation (e.g., isolated thrombocytosis with JAK2 V617F—to distinguish "masked PV" from ET).
• Suspected transformation to MF or AML.

Typical Findings in PV: [3]

• Hypercellular marrow (80-100% cellularity).
• Panmyelotic hyperplasia: Erythroid, granulocytic, and megakaryocytic lineages all increased.
• Megakaryocyte morphology: Pleomorphic, ranging from small to large forms; clustering common; normal to mildly increased in number (less pronounced than in ET).
• Absent or markedly reduced stainable iron (iron stores depleted by increased erythropoiesis).
• Mild to absent reticulin fibrosis (increased fibrosis suggests progression to post-PV MF).

Exam Detail: #### Red Cell Mass (RCM) Study

Historically the gold standard for diagnosing true erythrocytosis vs. relative polycythaemia. Now rarely performed due to:

• Availability of JAK2 mutation testing
• Revised WHO 2016 criteria with lower Hb/Hct thresholds
• Technical complexity (requires radioisotope labelling: ⁵¹Cr-RBC or ⁹⁹ᵐTc-RBC)

Remains useful:

• Young women with isolated thrombocytosis and JAK2 V617F positivity (plasma volume expansion may mask erythrocytosis → "masked PV").
• Cases with Hb/Hct just below WHO thresholds but strong clinical suspicion. [2]

Thresholds:

• Males: RCM > 36 mL/kg
• Females: RCM > 32 mL/kg

Ancillary Investigations

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7. Diagnostic Criteria

WHO 2016 Criteria for Polycythaemia Vera [3]

Major Criteria

1. Haemoglobin > 165 g/L (males) or > 160 g/L (females)

   OR

   Haematocrit > 0.49 (males) or > 0.48 (females)

   OR

   Increased red cell mass (> 25% above mean normal predicted)

2. Bone marrow biopsy showing hypercellularity for age with trilineage growth (panmyelosis) including prominent erythroid, granulocytic, and megakaryocytic proliferation with pleomorphic, mature megakaryocytes.

3. Presence of JAK2 V617F or JAK2 exon 12 mutation.

Minor Criterion

• Subnormal serum erythropoietin level.

Diagnostic Algorithm

Diagnosis of PV requires:

• All 3 major criteria

  OR

• First 2 major criteria + the minor criterion

Revised Thresholds (2016 vs. 2008 WHO)

The 2016 WHO revision lowered the Hb/Hct thresholds to improve detection of "masked PV":

This change aimed to distinguish masked PV from JAK2-mutated ET (where erythrocytosis may be present but below 2008 thresholds due to plasma volume expansion). [3]

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8. Risk Stratification

Thrombosis Risk Assessment

Age and thrombosis history are the two strongest predictors of future thrombotic events. [4]

Risk Categories

Additional Risk Factors (not used in standard 2-tier stratification but clinically relevant):

• Leukocytosis (WCC > 15 × 10⁹/L): Associated with increased arterial thrombosis. [16]
• JAK2 V617F allele burden (VAF > 75%): Higher thrombotic risk. [13]
• Cardiovascular risk factors: Hypertension, diabetes, smoking, hyperlipidaemia.
• Prior thrombosis in unusual sites (e.g., Budd-Chiari, portal vein thrombosis).

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9. Management

Overview of Treatment Strategy

Goals:

1. Reduce thrombotic risk (primary goal).
2. Control symptoms (pruritus, splenomegaly, hyperviscosity).
3. Prevent haemorrhagic complications.
4. Delay disease progression (to MF or AML).

Pillars of Treatment:

1. Therapeutic venesection (all patients).
2. Low-dose aspirin (all patients unless contraindicated).
3. Cytoreductive therapy (high-risk patients).
4. Cardiovascular risk factor modification (all patients).

Management Algorithm

                  POLYCYTHAEMIA VERA DIAGNOSED
                  (JAK2+, Raised Hb/Hct, Low EPO)
                              ↓
                     RISK STRATIFICATION
              ┌──────────────┴──────────────┐
         LOW RISK                       HIGH RISK
     (Age ≤60, No Thrombosis Hx)   (Age > 60 OR Prior Thrombosis)
              ↓                              ↓
       ┌──────────────┐              ┌─────────────────┐
       │ VENESECTION  │              │  VENESECTION    │
       │ + ASPIRIN    │              │  + ASPIRIN      │
       │              │              │  + CYTOREDUCTION│
       └──────────────┘              │  (Hydroxycarbamide)│
              ↓                      └─────────────────┘
       Target Hct less than 0.45                      ↓
              ↓                       Target Hct less than 0.45
        MONITOR FBC                    Monitor FBC monthly
       - Monthly initially            Watch for transformation
       - 3-monthly when stable        Consider Ruxolitinib if
       - Annual specialist review     resistant/intolerant to HU

1. Therapeutic Venesection (Phlebotomy)

Target: Haematocrit less than 0.45 in all patients. [7]

Evidence: CYTO-PV trial (NEJM 2013): [7]

• Randomised 365 PV patients to Hct target less than 0.45 vs. 0.45-0.50.
• Hct less than 0.45 group:
  • "Cardiovascular death or major thrombosis: HR 0.41 (p=0.007) — 59% risk reduction."
  • Benefit driven by reduction in cardiovascular deaths and major thromboses.
• Established less than 0.45 as the universal target irrespective of risk category.

Exam Detail: Venesection Protocol:

• Volume: 400-500 mL per session.
• Frequency:
  • "Induction phase: Weekly to fortnightly until Hct less than 0.45 achieved."
  • "Maintenance: As needed (PRN) to maintain Hct less than 0.45 (frequency varies: monthly to 3-monthly)."
• Monitoring: Check Hct before each venesection; aim to keep Hct consistently less than 0.45.
• Iron status: Venesection induces deliberate iron deficiency to limit erythropoiesis.
  • Do NOT supplement iron (iron repletion → rebound erythrocytosis).
  • Check ferritin periodically; target low/undetectable ferritin.

Elderly/Frail Patients:

• Reduce volume to 250-300 mL per session.
• Increase frequency to compensate.
• Monitor for symptomatic anaemia or cardiovascular decompensation.

Practical Tip:

• Venesection alone can control disease in low-risk patients for many years.
• Excessive venesection requirement (e.g., > 6-8 sessions/year) may warrant consideration of cytoreductive therapy even in low-risk patients.

2. Antiplatelet Therapy: Low-Dose Aspirin

Indication: All PV patients unless contraindicated. [6]

Evidence: ECLAP trial (NEJM 2004): [17]

• Randomised 518 PV patients to low-dose aspirin (100 mg daily) vs. placebo.
• Primary endpoint (CV death, non-fatal MI, non-fatal stroke, major venous thrombosis):
  • "Aspirin group: 1.6 events/100 patient-years"
  • "Placebo group: 3.9 events/100 patient-years"
  • RR 0.40 (60% reduction), p=0.03
• No significant increase in major bleeding in aspirin group.

Dose: 75-100 mg once daily.

Contraindications:

• Extreme thrombocytosis (> 1500 × 10⁹/L) with acquired vWD → paradoxical bleeding risk. [14]
  • In this scenario, omit aspirin until platelet count controlled with cytoreduction.
  • Consider PFA-100 or vWF studies if platelets > 1000 × 10⁹/L and bleeding symptoms present.
• Active peptic ulcer disease, significant bleeding history.
• Severe renal/hepatic impairment (consider dose reduction).

3. Cytoreductive Therapy

Indication: High-risk patients (age > 60 or prior thrombosis). [6]

First-Line: Hydroxycarbamide (Hydroxyurea)

Mechanism: Ribonucleotide reductase inhibitor → blocks DNA synthesis → preferentially inhibits rapidly dividing cells.

Dose:

• Starting dose: 500-1000 mg daily (15 mg/kg/day).
• Titrate to maintain:
  • Hct less than 0.45
  • Platelets 100-400 × 10⁹/L
  • WCC > 4 × 10⁹/L (avoid excessive myelosuppression)
• Maintenance dose: Typically 500-1500 mg daily (varies widely).

Monitoring:

• FBC weekly during dose escalation.
• FBC monthly once stable.
• LFTs, renal function 3-monthly.
• Annual skin examination (for cutaneous malignancies—debated association).

Side Effects:

• Macrocytosis (benign; inevitable).
• Myelosuppression (dose-limiting).
• Cutaneous: Leg ulcers (10-15%; more common in PV than ET), skin hyperpigmentation, facial/nail atrophy.
• Stomatitis, oral ulceration (5-10%).
• Theoretical leukaemogenicity: Controversial; large studies show no increased AML risk with HU monotherapy. [15]

Definition of Resistance/Intolerance: [18]

• Resistance:
  • Inability to achieve Hct less than 0.45 and/or platelet count less than 400 × 10⁹/L with maximum tolerated dose.
  • Persistent splenomegaly or disease-related symptoms despite 3 months of HU at adequate dose.
• Intolerance:
  • Development of ≥1 leg ulcers or other non-haematological toxicity necessitating discontinuation.
  • Hb less than 100 g/L or neutrophils less than 1.0 × 10⁹/L or platelets less than 100 × 10⁹/L at lowest dose required for disease control.

Alternative First-Line: Pegylated Interferon-Alpha (IFN-α)

Indications:

• Young patients (less than 60 years) requiring cytoreduction (to avoid long-term HU exposure).
• Pregnancy (IFN-α is pregnancy category C; HU is contraindicated).
• Hydroxyurea intolerance/resistance.

Forms:

• Peginterferon alfa-2a (Pegasys): 45-90 μg subcutaneously weekly.
• Peginterferon alfa-2b (PegIntron): 0.5-1.0 μg/kg subcutaneously weekly.
• Ropeginterferon alfa-2b (Besremi): 100-500 μg every 2 weeks (approved in EU 2019).

Mechanism: Immunomodulatory, anti-proliferative; may reduce JAK2 V617F allele burden (molecular responses seen in 10-30%). [19]

Side Effects:

• Flu-like symptoms (fever, myalgia, fatigue)—usually improve after first few weeks.
• Depression, mood disturbance (10-20%)—contraindicated in severe depression or suicide risk.
• Myelosuppression (less than HU).
• Thyroid dysfunction (monitor TSH every 3 months).
• Autoimmune phenomena (rare: thyroiditis, psoriasis exacerbation).

Monitoring:

• FBC monthly.
• LFTs, TSH every 3 months.
• Screen for depression at each visit.

Second-Line: Ruxolitinib (JAK1/JAK2 Inhibitor)

Indication: PV resistant to or intolerant of hydroxyurea. [18]

Evidence: RESPONSE trial (NEJM 2015): [18]

• 222 PV patients with HU resistance/intolerance randomised to ruxolitinib vs. best available therapy (BAT).
• Primary endpoint (Hct control + spleen volume reduction ≥35%):
  • "Ruxolitinib: 21%"
  • "BAT: 1% (pless than 0.001)"
• Secondary endpoints:
  • "Complete haematological remission: 24% vs. 9%."
  • "Symptom improvement (pruritus, fatigue): Marked benefit with ruxolitinib."

Dose:

• Starting dose: 10 mg twice daily.
• Titrate based on response and tolerability (maximum 25 mg twice daily).
• Monitor FBC every 2-4 weeks initially.

Side Effects:

• Anaemia (common; may require dose reduction or transfusions).
• Thrombocytopenia (less common).
• Infections (increased risk of herpes zoster—consider prophylactic aciclovir).
• Non-melanoma skin cancers (increased risk; annual dermatology review).
• Lipid abnormalities (monitor lipid profile).

Cost: Expensive; usually requires specialist approval.

Other Agents (Less Commonly Used)

4. Cardiovascular Risk Factor Modification

Essential in all patients: [6]

• Smoking cessation: Absolute priority (smoking markedly increases thrombotic risk).
• Blood pressure control: Target less than 130/80 mmHg.
• Diabetes management: HbA1c less than 53 mmol/mol (7%).
• Lipid management: Statins if indicated (10-year CVD risk > 10%).
• Weight management, regular exercise.

5. Management of Specific Complications

Aquagenic Pruritus

Stepwise Approach:

1. Avoid triggers: Warm water, tight clothing.
2. First-line:
   • Antihistamines: H₁-blockers (cetirizine, loratadine) + H₂-blockers (ranitidine) — often ineffective but worth trying.
   • Emollients: Menthol-based creams.
   • SSRI: Paroxetine 20 mg daily (surprisingly effective in 50-70%). [9]
3. Second-line:
   • UV-B phototherapy (narrow-band): Effective in refractory cases.
   • Interferon-alpha: Can be effective (immunomodulatory effect).
4. Ruxolitinib: Highly effective for refractory pruritus (one of the main indications for ruxolitinib in PV). [18]

Erythromelalgia

• Low-dose aspirin: Often dramatically effective (75-100 mg daily).
• If aspirin-refractory: Consider cytoreduction (hydroxyurea or interferon).

Hyperuricaemia/Gout

• Allopurinol: 100-300 mg daily (prophylaxis).
• Acute gout: NSAIDs or colchicine (standard gout management).

Thrombosis

Acute Management:

• Standard anticoagulation as per thrombosis type (e.g., LMWH/DOAC/warfarin for VTE; antiplatelet ± thrombolysis for arterial).
• Urgent venesection if Hct > 0.50 (reduce Hct to less than 0.45 rapidly).

Secondary Prevention:

• Long-term anticoagulation for VTE (indefinite duration given ongoing prothrombotic state).
• Intensify cytoreduction if thrombosis occurred despite treatment (consider switching to ruxolitinib or interferon).

Bleeding (Acquired von Willebrand Disease)

• Reduce platelet count urgently: Hydroxyurea or platelet apheresis (if life-threatening).
• Hold aspirin until platelets less than 1000-1500 × 10⁹/L.
• DDAVP (desmopressin): May be helpful acutely (releases vWF from endothelial stores).

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10. Complications

Thrombotic Complications

Incidence: ~2-5% per year depending on risk category and treatment adequacy. [4]

Arterial Thrombosis (50-60% of events)

Venous Thrombosis (40-50% of events)

Budd-Chiari Syndrome: [10]

• PV accounts for ~40% of Budd-Chiari cases.
• Presentation: Abdominal pain, hepatomegaly, ascites, elevated transaminases.
• Any young patient (less than 50 years) with Budd-Chiari should have JAK2 testing.

Haemorrhagic Complications

Incidence: 5-10% of patients (less common than thrombosis). [14]

Mechanisms:

• Acquired von Willebrand disease (extreme thrombocytosis > 1500 × 10⁹/L).
• Qualitative platelet dysfunction.
• Aspirin use (usually safe, but risk increases with extreme thrombocytosis).

Manifestations:

• Mucosal bleeding (epistaxis, gingival bleeding, menorrhagia).
• GI bleeding (especially if concurrent gastric/duodenal ulceration).
• Post-procedural bleeding.

Transformation (Late Complications)

Post-PV Myelofibrosis (Spent Phase)

Incidence: ~15% at 15 years; 20-25% at 20 years. [5]

Diagnostic Criteria (IWG-MRT 2007):

• Anaemia (Hb decline ≥20 g/L or Hb less than 100 g/L requiring transfusions).
• Leukoerythroblastic blood film: Nucleated RBCs, teardrop cells (dacrocytes).
• Increasing splenomegaly (> 5 cm below costal margin or > 10 cm by imaging).
• Bone marrow fibrosis (grade 2-3 reticulin or collagen fibrosis).

Clinical Features:

• Transition from proliferative to fibrotic phase.
• Progressive constitutional symptoms: Fatigue, weight loss, night sweats.
• Massive splenomegaly → abdominal discomfort, early satiety, splenic infarcts.
• Cytopenias (anaemia, thrombocytopenia).
• Extramedullary haematopoiesis (hepatomegaly, occasionally pleural/pulmonary involvement).

Management:

• Ruxolitinib: Improves spleen size and symptoms.
• Transfusion support (if anaemic).
• Allogeneic stem cell transplantation: Only curative option (consider in younger, fit patients).

Blast Transformation (Acute Leukaemia)

Incidence: 5-10% cumulative at 20 years. [5]

Risk Factors:

• Prior treatment with alkylating agents (busulfan, chlorambucil, ³²P)—largely historic now.
• Age > 70 years.
• Progression through myelofibrotic phase.
• Acquisition of high-risk mutations (TP53, IDH1/2, ASXL1).

Prognosis: Very poor; median survival less than 6 months. Refractory to conventional AML chemotherapy.

Management:

• Consider low-dose chemotherapy or hypomethylating agents (azacitidine, decitabine)—palliative intent.
• Allogeneic SCT if eligible (rarely feasible given age/comorbidities).
• Best supportive care.

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11. Prognosis and Outcomes

Survival

Causes of Death

Prognostic Factors

Favourable Prognostic Factors

• Age less than 60 years at diagnosis
• No prior thrombosis
• Good control of Hct (less than 0.45) and platelet count (less than 400 × 10⁹/L)
• Low JAK2 V617F allele burden (less than 50%)
• WCC less than 15 × 10⁹/L

Adverse Prognostic Factors

• Age > 60 years
• Prior thrombosis
• Leukocytosis (WCC > 15 × 10⁹/L)—associated with increased arterial thrombosis and transformation risk. [16]
• High JAK2 V617F allele burden (> 75%)
• Palpable splenomegaly (especially if progressive)
• Abnormal karyotype at diagnosis (rare in PV; suggests higher risk of transformation)

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12. Prevention and Screening

Primary Prevention

No established primary prevention (JAK2 mutations are acquired, not inherited).

Familial Risk:

• First-degree relatives have 5-7 fold increased risk of MPN. [12]
• No routine screening recommended for asymptomatic relatives (low absolute risk; no preventive intervention available).
• Consider FBC if symptoms develop.

Secondary Prevention (Preventing Complications)

Thrombosis Prevention:

1. Maintain Hct less than 0.45 (CYTO-PV trial). [7]
2. Low-dose aspirin 75-100 mg daily (ECLAP trial). [17]
3. Cytoreduction in high-risk patients (age > 60 or prior thrombosis).
4. Cardiovascular risk factor modification (smoking cessation, BP control, lipids, diabetes).

Prevent Progression:

• Avoid alkylating agents and ³²P (leukaemogenic).
• Unclear if any current therapy slows progression to MF or AML (interferon may have disease-modifying potential—under investigation).

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13. Key Guidelines and Evidence

Major Society Guidelines

Landmark Evidence

1. CYTO-PV Trial (NEJM 2013) [7]

Study: 365 PV patients randomised to Hct target less than 0.45 vs. 0.45-0.50.

Results:

• Primary endpoint (cardiovascular death or major thrombosis):
  • "Hct less than 0.45: 2.7%"
  • "Hct 0.45-0.50: 9.8%"
  • HR 0.41 (95% CI 0.18-0.91), p=0.007
• Impact: Established Hct less than 0.45 as the universal target in PV management (irrespective of age or thrombosis history).

2. ECLAP Trial (NEJM 2004) [17]

Study: 518 PV patients randomised to low-dose aspirin (100 mg daily) vs. placebo.

Results:

• Combined endpoint (CV death, non-fatal MI, non-fatal stroke, major venous thrombosis):
  • "Aspirin: 1.6 events/100 patient-years"
  • "Placebo: 3.9 events/100 patient-years"
  • RR 0.40 (60% reduction), p=0.03
• No significant increase in major bleeding.
• Impact: Low-dose aspirin became standard of care for all PV patients (unless contraindicated).

3. RESPONSE Trial (NEJM 2015) [18]

Study: 222 PV patients with hydroxyurea resistance/intolerance randomised to ruxolitinib vs. best available therapy.

Results:

• Primary endpoint (Hct control + spleen volume reduction ≥35%):
  • "Ruxolitinib: 21%"
  • "BAT: 1% (pless than 0.001)"
• Symptom improvement (pruritus, fatigue): Marked benefit with ruxolitinib.
• Impact: Ruxolitinib approved as second-line therapy for PV resistant/intolerant to hydroxyurea.

4. JAK2 V617F Discovery (Multiple Publications, 2005) [1]

Discovery: Independently reported by 4 groups in 2005 (Baxter et al., James et al., Kralovics et al., Levine et al.).

Impact:

• Revolutionised MPN diagnosis: JAK2 V617F present in 96% of PV, 55% of ET, 60% of PMF.
• Provided molecular confirmation of clonality.
• Opened avenue for targeted therapy (JAK inhibitors).

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14. Examination Focus

Common Exam Questions (MRCP, FRACP)

Written Exam (MCQ/SBA)

1. What is the target haematocrit in polycythaemia vera management?

   • A. less than 0.40
   • B. less than 0.42
   • C. less than 0.45 ✓ (CYTO-PV trial)
   • D. less than 0.50
   • E. less than 0.55

2. A 58-year-old man with PV presents with hepatic vein thrombosis (Budd-Chiari syndrome). Which intervention is most appropriate for thrombosis prevention?

   • A. Venesection alone
   • B. Aspirin alone
   • C. Cytoreductive therapy + aspirin + anticoagulation ✓ (High risk: prior thrombosis)
   • D. Observation
   • E. Warfarin alone

3. Which mutation is found in > 95% of PV patients?

   • A. BCR-ABL
   • B. CALR
   • C. MPL
   • D. JAK2 V617F ✓
   • E. TP53

4. A 35-year-old woman with PV (JAK2 V617F+) wishes to become pregnant. Which cytoreductive agent is safest?

   • A. Hydroxyurea (teratogenic—contraindicated)
   • B. Busulfan (teratogenic—contraindicated)
   • C. Ruxolitinib (limited data—avoid)
   • D. Interferon-alpha ✓ (safest option in pregnancy)
   • E. Anagrelide (avoid in pregnancy)

Viva Questions and Model Answers

Viva Point: Q1: "Tell me about polycythaemia vera."

Opening Statement: "Polycythaemia vera is a Philadelphia chromosome-negative myeloproliferative neoplasm characterised by clonal proliferation of haematopoietic stem cells leading to increased red cell mass, often with concurrent leukocytosis and thrombocytosis. It is driven by the JAK2 V617F mutation in over 95% of cases."

Key Points to Mention:

• Incidence: 1-2 per 100,000; median age 60-65 years.
• Pathophysiology: JAK2 V617F → constitutive activation of JAK2 tyrosine kinase → EPO-independent erythroid proliferation → low serum EPO.
• Clinical Features: Plethora, splenomegaly, hyperviscosity symptoms, aquagenic pruritus, thrombotic events (arterial and venous, including unusual sites like Budd-Chiari).
• Diagnosis: WHO 2016 criteria—elevated Hb/Hct + JAK2 mutation + low EPO (± bone marrow biopsy).
• Complications: Thrombosis (30-40% of deaths), transformation to myelofibrosis (15% at 15 years), AML (5-10%).
• Management: Venesection to Hct less than 0.45 (CYTO-PV trial), low-dose aspirin (ECLAP trial), cytoreduction (hydroxyurea or interferon) in high-risk patients (age > 60 or prior thrombosis).

Viva Point: Q2: "How do you distinguish polycythaemia vera from secondary polycythaemia?"

Structured Answer: "The key distinguishing features are:

Clinical:

• PV: Splenomegaly, aquagenic pruritus, erythromelalgia, panmyelosis (raised WCC/Plt).
• Secondary: Features of underlying cause (e.g., cyanosis in COPD, renal mass in RCC).

Laboratory:

• JAK2 V617F: Positive in PV (> 95%), negative in secondary.
• Serum EPO: Low/normal in PV, high in secondary polycythaemia (appropriate if hypoxic, inappropriate if EPO-secreting tumour).
• FBC: Isolated erythrocytosis in secondary (usually); panmyelosis in PV.
• Oxygen saturation: Low in hypoxic secondary polycythaemia; normal in PV.

Bone Marrow:

• PV: Hypercellular, panmyelotic hyperplasia, pleomorphic megakaryocytes.
• Secondary: Erythroid hyperplasia only; normal megakaryocytes.

In practice, a positive JAK2 V617F with low/normal EPO is virtually diagnostic of PV."

Viva Point: Q3: "What is the significance of the CYTO-PV trial?"

Answer: "The CYTO-PV trial, published in the New England Journal of Medicine in 2013, was a randomised controlled trial comparing two haematocrit targets in 365 PV patients:

• Group 1: Hct less than 0.45
• Group 2: Hct 0.45-0.50

Results:

• The primary endpoint (cardiovascular death or major thrombosis) occurred in 2.7% of the Hct less than 0.45 group vs. 9.8% of the 0.45-0.50 group.
• Hazard ratio 0.41 (59% risk reduction), p=0.007.

Impact:

• Established Hct less than 0.45 as the universal target for all PV patients, irrespective of age or risk category.
• This is now incorporated into all international guidelines (BSH, ELN, NCCN) and is a cornerstone of PV management."

Common Mistakes

❌ Failing to test for JAK2 exon 12 mutations when V617F is negative but PV is strongly suspected (isolated erythrocytosis, low EPO, erythroid-predominant marrow).

❌ Treating elevated haematocrit alone without checking for underlying causes (PV vs. secondary polycythaemia vs. relative polycythaemia).

❌ Giving iron supplementation to PV patients with low ferritin—this is counterproductive (iron fuels erythropoiesis).

❌ Not screening for Budd-Chiari syndrome in young patients with hepatic vein thrombosis (PV is the most common cause).

❌ Using venesection alone in high-risk patients (age > 60 or prior thrombosis)—these patients require cytoreductive therapy.

❌ Continuing aspirin in patients with extreme thrombocytosis (> 1500 × 10⁹/L) and bleeding—risk of acquired vWD.

❌ Using alkylating agents (busulfan, chlorambucil) or radioactive phosphorus (³²P) as first-line cytoreduction—these are leukaemogenic and outdated.

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15. Patient and Layperson Explanation

What is Polycythaemia Vera?

Polycythaemia vera (often shortened to "PV") is a rare blood disorder where your bone marrow (the "factory" inside your bones that makes blood cells) produces too many red blood cells.

Normally, your body carefully controls how many red blood cells you have, using a hormone called erythropoietin (EPO). In PV, a change (called a mutation) in a gene called JAK2 causes the bone marrow to ignore these normal controls and keep making red cells even when you don't need them.

What causes it?

PV is caused by a mutation (change) in the JAK2 gene that happens during your life—it's not something you're born with or inherit from your parents, and you can't pass it on to your children.

We don't know exactly why this mutation happens, but it's not caused by anything you did (like smoking or diet). It's just an unlucky random event in one of your bone marrow cells.

Why is having too many red blood cells a problem?

Red blood cells carry oxygen around your body, so you might think "more is better." However, having too many makes your blood thick and sticky, like honey instead of water. This causes several problems:

1. Increased risk of blood clots (thrombosis):

   • Clots in the brain → stroke
   • Clots in the heart → heart attack
   • Clots in the legs → deep vein thrombosis (DVT)
   • Clots in unusual places like the liver (Budd-Chiari syndrome)

2. Headaches, dizziness, and blurred vision (because thick blood flows slowly to your brain and eyes).

3. Itching (especially after a hot shower or bath)—this is very common in PV and can be one of the most bothersome symptoms.

4. Red, flushed face (plethora) from all the extra red cells.

How is it diagnosed?

Your doctor will:

1. Do a blood test to check your haemoglobin (Hb) and haematocrit (Hct)—these measure how many red cells you have.
2. Test for the JAK2 mutation (a simple blood test).
3. Measure your EPO level (this is usually low in PV).
4. Sometimes take a small sample from your bone marrow (bone marrow biopsy) to look at the cells under a microscope.

How is it treated?

The good news is that PV can be controlled very effectively with treatment. The goals are to:

• Reduce the number of red blood cells (thin your blood).
• Prevent blood clots.

Treatments include:

1. Venesection (Phlebotomy): Like blood donation—we remove 400-500 mL of blood every few weeks to bring your haematocrit down to a safe level (less than 0.45). This is the most important treatment for everyone with PV.

2. Aspirin: A low dose (75-100 mg) once a day to reduce the risk of clots. This is safe for most people and has been proven to cut the clot risk by about 60%.

3. Tablets (Cytoreductive Therapy): If you're at higher risk of clots (age over 60 or if you've had a clot before), we may add a tablet to slow down your bone marrow:

   • Hydroxycarbamide (Hydroxyurea): The most common tablet used.
   • Interferon-alpha: An injection, preferred in younger patients or if you're pregnant.
   • Ruxolitinib: A newer tablet if the others don't work or cause side effects.

4. Control other risk factors: Stop smoking, manage blood pressure and cholesterol, keep active.

What is the outlook?

With good treatment, most people with PV live for many years—often 15-20 years or more. You'll need regular blood tests and check-ups, but many people with PV lead full, active lives.

The main risks are:

• Blood clots: The most common serious complication, but this risk is greatly reduced by treatment.
• Progression: Over many years (usually 10-20+), PV can sometimes change into other conditions like myelofibrosis (where your bone marrow becomes scarred) or, rarely, leukaemia. We monitor for this with regular check-ups.

What should I watch out for?

Contact your doctor urgently if you develop:

• Symptoms of a stroke (sudden weakness, speech problems, facial droop).
• Symptoms of a heart attack (chest pain, shortness of breath).
• Severe headache (could be a clot in the brain).
• Leg swelling or pain (could be a DVT).
• Abdominal pain with swelling (could be a clot in abdominal veins).
• Unexplained bleeding or bruising.

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16. References

Primary Sources

1. Harrison CN, Barbui T, Bose P, et al. Polycythaemia vera. Nat Rev Dis Primers. 2025;11(1):26. doi:10.1038/s41572-025-00608-3

2. Spivak JL. Polycythemia Vera. Curr Treat Options Oncol. 2018;19(2):12. doi:10.1007/s11864-018-0529-x

3. Barbui T, Thiele J, Gisslinger H, et al. The 2016 WHO classification and diagnostic criteria for myeloproliferative neoplasms: document summary and in-depth discussion. Blood Cancer J. 2018;8(2):15. doi:10.1038/s41408-018-0054-y

4. Tefferi A, Barbui T. Polycythemia vera and essential thrombocythemia: 2021 update on diagnosis, risk-stratification and management. Am J Hematol. 2020;95(12):1599-1613. doi:10.1002/ajh.26008

5. Cerquozzi S, Tefferi A. Blast transformation and fibrotic progression in polycythemia vera and essential thrombocythemia: a literature review of incidence and risk factors. Blood Cancer J. 2015;5(11):e366. doi:10.1038/bcj.2015.95

6. McMullin MF, Harrison CN, Ali S, et al. A guideline for the diagnosis and management of polycythaemia vera. A British Society for Haematology Guideline. Br J Haematol. 2019;184(2):176-191. doi:10.1111/bjh.15648

7. Marchioli R, Finazzi G, Specchia G, et al. Cardiovascular events and intensity of treatment in polycythemia vera. N Engl J Med. 2013;368(1):22-33. doi:10.1056/NEJMoa1208500

8. Tefferi A, Rumi E, Finazzi G, et al. Survival and prognosis among 1545 patients with contemporary polycythemia vera: an international study. Leukemia. 2013;27(9):1874-1881. doi:10.1038/leu.2013.163

9. Siegel FP, Tauscher J, Petrides PE. Aquagenic pruritus in polycythemia vera: characteristics and influence on quality of life in 441 patients. Am J Hematol. 2013;88(8):665-669. doi:10.1002/ajh.23474

10. Smalberg JH, Arends LR, Valla DC, et al. Myeloproliferative neoplasms in Budd-Chiari syndrome and portal vein thrombosis: a meta-analysis. Blood. 2012;120(25):4921-4928. doi:10.1182/blood-2011-09-376517

11. Moulard O, Mehta J, Fryzek J, et al. Epidemiology of myelofibrosis, essential thrombocythemia, and polycythemia vera in the European Union. Eur J Haematol. 2014;92(4):289-297. doi:10.1111/ejh.12256

12. Landgren O, Goldin LR, Kristinsson SY, et al. Increased risks of polycythemia vera, essential thrombocythemia, and myelofibrosis among 24,577 first-degree relatives of 11,039 patients with myeloproliferative neoplasms in Sweden. Blood. 2008;112(6):2199-2204. doi:10.1182/blood-2008-03-143602

13. Vannucchi AM, Antonioli E, Guglielmelli P, et al. Prospective identification of high-risk polycythemia vera patients based on JAK2(V617F) allele burden. Leukemia. 2007;21(9):1952-1959. doi:10.1038/sj.leu.2404854

14. Mital A, Prejzner W, Bieniaszewska M, et al. Prevalence of acquired von Willebrand syndrome during polycythemia vera and essential thrombocythemia: association with the JAK2 V617F mutation, leukocytosis, and platelet count. Leuk Lymphoma. 2013;54(12):2606-2609. doi:10.3109/10428194.2013.781167

15. Finazzi G, Caruso V, Marchioli R, et al. Acute leukemia in polycythemia vera: an analysis of 1638 patients enrolled in a prospective observational study. Blood. 2005;105(7):2664-2670. doi:10.1182/blood-2004-09-3426

16. Barbui T, Carobbio A, Rumi E, et al. In contemporary patients with polycythemia vera, rates of thrombosis and risk factors delineate a new clinical epidemiology. Blood. 2014;124(19):3021-3023. doi:10.1182/blood-2014-07-591610

17. Landolfi R, Marchioli R, Kutti J, et al. Efficacy and safety of low-dose aspirin in polycythemia vera. N Engl J Med. 2004;350(2):114-124. doi:10.1056/NEJMoa035572

18. Vannucchi AM, Kiladjian JJ, Griesshammer M, et al. Ruxolitinib versus standard therapy for the treatment of polycythemia vera. N Engl J Med. 2015;372(5):426-435. doi:10.1056/NEJMoa1409002

19. Kiladjian JJ, Cassinat B, Chevret S, et al. Pegylated interferon-alfa-2a induces complete hematological and molecular responses with low toxicity in polycythemia vera. Blood. 2008;112(8):3065-3072. doi:10.1182/blood-2008-03-143537

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