Polycythemia Vera

Slide 1 · Polycythemia Vera

Clonal panmyelosis · JAK2 signaling · Vascular complications

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Explain how JAK2 activation produces growth-factor–independent hematopoiesis.

Recognize panmyelosis and its marrow and blood manifestations.

Connect erythrocytosis and platelet dysfunction to vascular events.

Distinguish PV from relative/secondary polycythemia and related MPNs.

Describe post-PV myelofibrosis and leukemic transformation.

Slide 3 · PV within the myeloproliferative neoplasms

Myeloproliferative neoplasms

PV

Essential thrombocythemia

Primary myelofibrosis

CML

Classification context: Kinase signaling abnormalities with overlapping phenotypes

Slide 4 · The defining marrow phenotype is panmyelosis

Clonal myeloid progenitor

Erythroid precursors

Red cell mass ↑

Granulocytic precursors

Leukocytes ↑

Megakaryocytes

Platelets ↑

Simplified lineage model — not a marrow section

Slide 5 · Why red cell expansion matters most

Red cell expansion

High hematocrit

Viscosity / disturbed flow

Vascular consequences

Increased red cell mass elevates the hematocrit.

Viscosity and altered microvascular flow connect cell production to symptoms.

The other two lineages contribute to thrombosis and hemorrhage.

Conceptual causal sequence — native, editable schematic

Slide 6 · PV is clonal rather than a physiologic response

Acquired clone

Growth-factor independence

Maturing hematopoiesis

Expanded cell numbers

The proliferating progenitor has acquired an oncogenic signaling alteration.

The cell responds less to normal hematopoietic growth-factor control.

Mature circulating cells increase because differentiation is largely preserved.

Conceptual causal sequence — native, editable schematic

Slide 7 · Normal erythropoiesis is EPO responsive

EPO signal

EPO receptor / JAK2

Erythroid survival and output

Feedback reduces EPO

Erythropoietin (EPO) stimulates erythroid progenitors through the EPO receptor.

Intracellular JAK2 participates in receptor-linked growth signaling.

Rising red cell mass normally suppresses further EPO production.

Conceptual causal sequence — native, editable schematic

Slide 8 · The JAK–STAT axis links receptors to gene expression

EPO ligand

EPO receptor / JAK2

STAT signaling

Progenitor proliferation and survival

Normal EPO ligand binding activates the receptor-linked JAK2 pathway.

Activated STAT proteins support erythroid progenitor survival and growth.

Normal receptor signaling schematic

Slide 9 · Activating JAK2 mutations bypass normal restraint

Activating JAK2 mutation

EPO receptor / JAK2

STAT signaling

Progenitor proliferation and survival

Mutant JAK2 permits signaling with markedly reduced EPO dependence.

Persistent signaling drives clonal expansion of mature blood elements.

Constitutive signaling schematic

Slide 10 · JAK2 V617F is the predominant driver

JAK2 V617F

Valine (V)

Phenylalanine (F)

Residue 617 substitution — not a sequence-scale representation

Slide 11 · The JAK2 variant is not the same as the blood-count phenotype

Driver genotype

Disease phenotype

The mutation establishes proliferative signaling potential.

Cell lineage output and marrow context determine observed counts.

The same JAK2 mutation may also occur in related MPN phenotypes.

Slide 12 · Growth-factor independence is relative at the bedside

Physiologic erythropoiesis

PV erythropoiesis

PV progenitors have markedly reduced growth-factor requirements.

The clinical clue is inappropriate erythropoiesis despite suppressed EPO.

Do not equate a suppressed EPO with absent receptor-signaling activity.

Slide 13 · Serum EPO is often suppressed in PV

Clonal erythroid output increases

Circulating EPO decreases

JAK2-mutant progenitors remain active

Suppressed EPO does not switch off an autonomous JAK2 clone

Slide 14 · PV and secondary erythrocytosis have opposite EPO logic

PV: Low EPO

Secondary: Elevated EPO

PV: An autonomous marrow clone expands red cells despite low EPO.

Secondary erythrocytosis: Increased EPO drives a compensatory red cell response.

EPO is a discriminating clue, not a stand-alone diagnosis.

Slide 15 · Additional JAK2 alleles can influence the phenotype

One mutated allele

Two mutated alleles

The source describes two mutant JAK2 copies in approximately 25%–30% of cases.

Such cases were associated with higher leukocyte counts, splenomegaly, pruritus, and fibrotic progression.

This association is not an individual prognosis for a new patient.

Slide 16 · PV proliferates less aggressively than CML

PV / JAK2

CML / BCR::ABL

PV generally has less striking leukocytosis and marrow hypercellularity.

CML is driven by BCR::ABL and often has pronounced granulocytic expansion.

The two kinases produce distinguishable clinicopathologic phenotypes.

Slide 17 · Hematocrit links marrow output to viscosity

Erythroid expansion

Hematocrit rises

Viscosity increases

Flow slows

Higher red cell fraction increases resistance to blood flow.

Blood sludging becomes particularly relevant in low-pressure vascular beds.

This hemodynamic change contributes to microvascular and major vascular events.

Conceptual causal sequence — native, editable schematic

Slide 18 · The venous circulation is especially vulnerable

RBC-rich blood in low-pressure peripheral vessels

Distension + sluggish transit → increased local deoxygenation

Circulatory illustration — not an anatomic vessel cross-section

Slide 19 · Platelets are numerous but not necessarily normal

Platelet quantity ↑

Platelet quality impaired

Thrombocytosis frequently accompanies erythrocytosis.

Large, morphologically abnormal platelets may circulate.

Aggregation studies can demonstrate qualitative platelet defects.

Slide 20 · Thrombosis and hemorrhage can coexist

PV blood phenotype

Thrombosis

Hemorrhage

Viscosity / abnormal flow

Abnormal platelet function

Slide 21 · Bone marrow morphology: Hypercellularity

Hypercellular marrow

Some residual fat

Trilineage expansion

Simplified editable cellularity schematic — not genuine H&E

Slide 22 · Recognize the three expanding hematopoietic lineages

Clonal myeloid progenitor

Erythroid precursors

Red cell mass ↑

Granulocytic precursors

Leukocytes ↑

Megakaryocytes

Platelets ↑

Simplified lineage model — not a marrow section

Slide 23 · Erythroid expansion can appear subtle in biopsy

Subtle erythroid expansion

Read all three lineages

Correlate with counts

Simplified editable cellularity schematic — not genuine H&E

Slide 24 · Granulocytic expansion accompanies erythrocytosis

The marrow often contains increased granulocytic precursors.

Mature blood granulocytes may also be elevated.

Panmyelosis is therefore not synonymous with isolated erythroid hyperplasia.

Slide 25 · Megakaryocytes add a distinct morphologic clue

Megakaryocytes ↑

Giant platelets possible

Assess panmyelosis

Simplified editable cellularity schematic — not genuine H&E

Slide 26 · Residual marrow fat need not disappear

Normal-context marrow

PV marrow

PV marrow can be hypercellular with residual adipose spaces.

The pattern is not the uniformly packed marrow often seen in untreated CML.

Degree of cellularity must be judged in clinical and age context.

Slide 27 · Reticulin increase may occur at diagnosis

Moderate-to-marked reticulin in about 10% of presenting marrow samples.

Reticulin increase is not automatically equivalent to post-PV myelofibrosis.

Stage interpretation requires the broader clinicopathologic picture.

Slide 28 · Early organomegaly need not mean extensive EMH

Early congestion

Advanced EMH

Mild organomegaly can reflect vascular congestion early in PV.

Extramedullary hematopoiesis (EMH) is limited in this phase.

In advanced myelofibrosis, EMH becomes much more prominent.

Slide 29 · Peripheral blood: Think beyond RBC count

Increased basophils may be present.

Platelets can be abnormally large.

A smear complements the complete blood count but does not establish PV by itself.

Slide 30 · Insidious onset in later adulthood

PV most often in adults of late middle age.

The reported U.S. Incidence is approximately 1–3 per 100,000 people per year.

Symptoms may evolve before the myeloproliferative disorder is recognized.

Slide 31 · A raised red cell mass changes the circulating volume

Red cell mass ↑

Blood volume often ↑

Venous distension

Symptoms

Total blood volume is commonly increased in PV.

Venous distension and diminished flow efficiency help explain physical findings.

Volume expansion and viscosity should be considered together.

Conceptual causal sequence — native, editable schematic

Slide 32 · Plethora and cyanosis reflect peripheral stasis

RBC-rich blood in low-pressure peripheral vessels

Distension + sluggish transit → increased local deoxygenation

Circulatory illustration — not an anatomic vessel cross-section

Slide 33 · Headache and dizziness are hemodynamic clues

Disordered microvascular flow provides a mechanistic explanation.

These symptoms are common but are nonspecific.

Their value increases when accompanied by elevated hematocrit and other PV findings.

Slide 34 · Hypertension and gastrointestinal complaints may occur

Expanded blood volume is relevant to blood-pressure changes.

Gastrointestinal symptoms are among the clinical manifestations described.

Neither feature is independently diagnostic.

Slide 35 · Pruritus may relate to basophil mediators

Basophil expansion

Mediator release proposed

Pruritus

The textbook links intense pruritus possibly to basophil histamine release.

Basophils may be elevated in peripheral blood.

This proposed mechanism is a possibility, not proof of a single pathway.

Conceptual causal sequence — native, editable schematic

Slide 36 · Peptic ulceration is another possible mediator effect

Peptic ulceration occurs in the clinical description of PV.

Histamine release from basophils is offered as a possible mechanism.

The causal explanation should be taught as uncertain.

Slide 37 · High turnover can produce hyperuricemia

Increased cell turnover

Purine catabolism

Hyperuricemia

Secondary gout

Increased blood-cell production also increases cellular turnover.

Purine breakdown can elevate serum uric acid.

Symptomatic secondary gout in about 5%–10% of cases.

Conceptual causal sequence — native, editable schematic

Slide 38 · Major thrombosis may be the first presentation

Approximately one-quarter of patients presenting with a vascular event.

Deep venous thrombosis, myocardial infarction, and stroke are examples.

Thrombosis can precede obvious hematologic abnormalities.

Slide 39 · Venous thrombosis has several clinical faces

Deep venous thrombosis is an important presenting manifestation.

Venous stasis is a plausible contributor, alongside cellular and platelet changes.

The clot location influences symptoms and the diagnostic pathway.

Slide 40 · Arterial events are part of the same disease spectrum

PV blood phenotype

Disturbed flow + platelets

Arterial thrombosis

Infarction

Myocardial infarction and stroke may bring PV to attention.

High hematocrit and abnormal platelet biology are both relevant.

A vascular event should prompt evaluation of otherwise unexplained erythrocytosis.

Conceptual causal sequence — native, editable schematic

Slide 41 · Splanchnic thrombosis deserves attention

Hepatic vein thrombosis may produce Budd–Chiari syndrome.

Portal and mesenteric venous thromboses are also described.

Mesenteric venous occlusion can progress to bowel infarction.

Slide 42 · Do not wait for classic blood counts after thrombosis

Thrombotic episodes may precede the textbook hematologic pattern.

A single hematocrit measurement must be interpreted in context.

Clinical suspicion may remain high despite initially ambiguous counts.

Slide 43 · Bleeding commonly involves mucosal surfaces

Epistaxis and gum bleeding are frequently described.

Major bleeding is less common but can be life-threatening.

The textbook estimates life-threatening hemorrhage in roughly 5%–10% of cases.

Slide 44 · The platelet paradox is functional, not numerical

More platelets

Impaired function

Elevated platelet count does not exclude impaired aggregation.

Large forms and abnormal functional tests indicate dysregulated megakaryopoiesis.

Bleeding and thrombosis are therefore not mutually exclusive outcomes.

Slide 45 · Hemoglobin and hematocrit: Typical textbook findings

Hemoglobin: Often >16 g/dL

Hematocrit: Often ≥55%

Descriptive textbook values — not formal diagnostic criteria

Slide 46 · Leukocyte and platelet abnormalities support panmyelosis

WBC: 12,000–50,000/mm³

Platelets: Often >500,000/mm³

Descriptive textbook values — not formal diagnostic criteria

Slide 47 · Iron deficiency can disguise red cell overproduction

Chronic blood loss may deplete iron stores.

Restricted hemoglobin synthesis can reduce the measured hematocrit.

Underlying PV can therefore coexist with a deceptively normal hematocrit.

Slide 48 · Two abnormalities can counteract on a blood test

PV: Erythroid drive ↑

Iron deficiency: Hb synthesis ↓

Measured hematocrit can appear normal

Slide 49 · Interpret the CBC as a pattern, not a verdict

Assess red cell indices, white cell count, and platelet count together.

Link blood counts with marrow morphology and molecular findings.

Review iron status when counts and the clinical pattern appear discordant.

Slide 50 · First differentiate relative from absolute polycythemia

Elevated or suspicious hematocrit

Relative / hemoconcentration

Absolute erythrocytosis

PV: JAK2 clone, often low EPO

Secondary: Often high EPO

Conceptual diagnostic classification; Not a validated clinical algorithm

Slide 51 · Secondary erythrocytosis is not PV

Clonal PV

EPO-mediated erythrocytosis

Secondary forms are stimulated by elevated EPO, unlike the usual low EPO of PV.

Physiologic or pathological drivers outside a JAK2-mutant marrow must be evaluated.

The textbook directs readers to the subsequent erythrocytosis chapter.

Slide 52 · Integrated diagnostic reasoning for suspected PV

An elevated hematocrit triggers evaluation, not an automatic PV label.

Consider hemoconcentration, secondary erythrocytosis, and masking iron deficiency.

Integrate JAK2 mutation testing, EPO, peripheral counts, and marrow findings.

Slide 53 · PV versus essential thrombocythemia

Polycythemia vera

Essential thrombocythemia

Both can harbor JAK2 mutations and have high platelet counts.

PV has erythrocytosis with panmyelosis; ET is clinically platelet-dominant.

Iron deficiency can obscure the erythrocytosis of PV.

Slide 54 · PV versus chronic myeloid leukemia

JAK2 / PV

BCR::ABL / CML

JAK2-driven PV commonly produces erythrocytosis and trilineage proliferation.

BCR::ABL-driven CML usually produces far greater granulocytic proliferation.

Molecular markers distinguish their defining oncogenic pathways.

Slide 55 · PV versus primary myelofibrosis

PV phase

Primary myelofibrosis

Early PV emphasizes increased red cell mass and panmyelosis.

Primary myelofibrosis is a separate MPN with a fibrotic marrow phenotype.

Post-PV myelofibrosis is an acquired late disease phase, not an initial synonym.

Slide 56 · Case 1: An unexpected venous thrombosis

A late-middle-aged adult develops hepatic vein thrombosis.

Investigations reveal an elevated hematocrit and increased platelet count.

What pathophysiologic links and diagnostic distinctions should be considered?

Discussion: Form a mechanistic differential

Slide 57 · Case 1: Reasoning from the vascular event

Unusual venous thrombosis is a recognized PV presentation.

Increased red cell mass can raise viscosity; Platelet abnormalities add risk.

Differentiate relative and secondary erythrocytosis before concluding PV.

Discussion: Expected reasoning

Slide 58 · Phlebotomy targets the red cell burden

Phlebotomy

Red cell mass falls

Hematocrit lowers

Viscosity burden reduced

Reducing red cell mass addresses the principal hemodynamic driver.

Phlebotomy as a major strategy for PV control.

Treatment targets should follow current specialty guidance, not a descriptive hematocrit from the excerpt.

Conceptual causal sequence — native, editable schematic

Slide 59 · Low-dose aspirin addresses vascular risk

Red cell component

Platelet component

The Robbins treatment discussion pairs phlebotomy with low-dose aspirin.

The rationale is mitigation of platelet-mediated thrombotic risk.

Clinical use must account for bleeding risk and current guidance.

Slide 60 · Current practice: JAK inhibitor eligibility differs

Robbins textbook framing

Verified 2026 U.S. Label

Describes use of JAK2 inhibitors primarily after progression to a fibrotic phase.

Ruxolitinib is also indicated for adult PV after inadequate response or intolerance to hydroxyurea.

Separately sourced contemporary clarification

Slide 61 · Post-PV myelofibrosis changes the marrow architecture

Proliferative phase

Fibrotic “spent” phase

Stage schematic; Not histologic evidence or measured fibrosis

Slide 62 · The spleen can become a major hematopoietic site

Marrow fibrosis

Marrow space lost

Splenic EMH

Marked splenomegaly

As marrow function becomes impaired, extramedullary hematopoiesis increases.

The spleen may enlarge dramatically during the spent phase.

Late splenomegaly reflects a different mechanism from early congestion.

Conceptual causal sequence — native, editable schematic

Slide 63 · The transition to a spent phase is not universal

Proliferative PV

Subset develops fibrosis

Post-PV myelofibrosis

Robbins: Fibrosis in ~15%–20% after an average of ~10 years

Slide 64 · Acute myeloid leukemia is an uncommon outcome

Chronic PV clone

Additional oncogenic evolution

AML in a minority

A small fraction of PV patients develop AML.

The extracted textbook passages report discordant approximate frequencies (1% and 2%).

A single precise transformation percentage is therefore deliberately not presented.

Conceptual causal sequence — native, editable schematic

Slide 65 · Leukemic clones may not retain the JAK2 alteration

Abnormal ancestral progenitor

JAK2-mutant PV lineage

Divergent AML lineage

Mechanistic model inferred from discordant JAK2 status in some AML clones

Slide 66 · The proposed cell of origin remains a mechanistic inference

The text favors an abnormal progenitor with myeloid commitment for PV.

Transformation to acute lymphoblastic leukemia is rare, unlike the broader lineage potential in CML.

Clonal evolution is more complex than a linear JAK2-only model.

Slide 67 · Case 2: A “normal” hematocrit with clues to PV

A patient has pruritus, thrombocytosis, leukocytosis, and iron deficiency.

The hematocrit is not markedly increased despite other myeloproliferative clues.

What could be masking red cell expansion?

Discussion: Form a mechanistic differential

Slide 68 · Case 2: Interpret the countervailing defects

Iron deficiency can limit erythropoiesis enough to lower the hematocrit.

Consider masked PV instead of assuming isolated thrombocythemia.

The full work-up requires integrated blood, marrow, EPO, and molecular data.

Discussion: Expected reasoning

Slide 69 · Polycythemia vera: Integrated disease sequence

JAK2 activation

Panmyelosis

Vascular risks

Possible progression

Diagnosis requires integrated clinicopathologic interpretation.

Slide 70 · Reference and interpretation notes

Primary text: Robbins, Cotran & Kumar, Pathologic Basis of Disease, 11th ed., Chapter 13, pp. 568–569.

Treatment update: U.S. FDA ruxolitinib label (2026), adults with inadequate response/intolerance to hydroxyurea.

Textbook numerical observations are distinguished from formal diagnostic criteria.

No chapter PDF was supplied; source passages were reconstructed from column-interleaved Markdown.