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Myeloproliferative Neoplasms — MRCP Part 1

TL;DR

For MRCP Part 1, myeloproliferative neoplasms (PV, ET, and myelofibrosis) are high-yield due to their overlapping features and exam-favoured laboratory distinctions. Focus on JAK2 mutations, erythropoietin levels, thrombotic risk, and blood film findings. Recognising key differentiators—especially low EPO in PV and tear-drop cells in myelofibrosis—will help you avoid common traps.


Why this matters

Myeloproliferative neoplasms (MPNs) are a core haematology topic in MRCP Part 1, frequently tested through clinical vignettes and lab interpretation. Candidates are expected to distinguish between PV, ET, and myelofibrosis using subtle but high-yield clues.

You can reinforce this topic within the broader syllabus via the MRCP Part 1 overview and consolidate practice using Free MRCP MCQs.


Core sections

1. Classification of MPNs

The classical Philadelphia chromosome-negative MPNs include:

  • Polycythaemia vera (PV)

  • Essential thrombocythaemia (ET)

  • Primary myelofibrosis (PMF)

All are clonal haematopoietic stem cell disorders characterised by overproduction of myeloid cells.

2. Genetic mutations (Very high-yield)

  • JAK2 V617F mutation

    • ~95% of PV

    • ~50–60% of ET and PMF

  • CALR mutation → seen in JAK2-negative ET/PMF

  • MPL mutation → less common

📌 Exam insight:A combination of JAK2 positivity + low erythropoietin (EPO) strongly suggests PV.

3. Key distinguishing features

Feature

Polycythaemia Vera (PV)

Essential Thrombocythaemia (ET)

Myelofibrosis (PMF)

Main abnormality

↑ RBC mass

↑ Platelets

Marrow fibrosis

Hb/Hct

Markedly ↑

Normal/slight ↑

Variable

Platelets

↑

Markedly ↑

Variable

EPO level

↓

Normal

Normal

Splenomegaly

Common

Mild

Marked

Blood film

Plethoric picture

Giant platelets

Tear-drop cells

4. Clinical features (Classic exam stems)

Polycythaemia vera (PV):

  • Headache, dizziness

  • Aquagenic pruritus (after hot bath)

  • Ruddy complexion

Essential thrombocythaemia (ET):

  • Thrombosis (e.g. stroke, DVT)

  • Paradoxical bleeding

  • Often incidental finding

Primary myelofibrosis (PMF):

  • Massive splenomegaly

  • Fatigue, weight loss

  • Anaemia and constitutional symptoms

5. Complications (Frequently tested)

  • Arterial and venous thrombosis

  • Haemorrhage (especially in ET)

  • Progression to myelofibrosis

  • Transformation to acute myeloid leukaemia (AML)

6. Investigations (Pattern recognition)

  • Full blood count (FBC)

  • JAK2 mutation testing

  • Serum erythropoietin

  • Bone marrow biopsy (especially for PMF)

7. Management principles (Exam basics)

Polycythaemia vera:

  • Venesection (target haematocrit <45%)

  • Low-dose aspirin

  • Cytoreduction (e.g. hydroxycarbamide)

Essential thrombocythaemia:

  • Risk stratification

  • Aspirin ± cytoreduction

Myelofibrosis:

  • Supportive care (transfusions)

  • JAK inhibitors (e.g. ruxolitinib)

  • Stem cell transplant (selected patients)

8. Five most tested subtopics

  1. JAK2 mutation prevalence

  2. Low EPO in PV

  3. Tear-drop cells in myelofibrosis

  4. Thrombosis risk patterns

  5. Transformation to AML

9. Five exam traps

  1. Raised Hb is not always PV (consider hypoxia, smoking)

  2. Normal platelets do not exclude early ET

  3. Raised EPO argues against PV

  4. Splenomegaly severity points towards myelofibrosis

  5. Misidentifying blood film findings

10. High-yield revision checklist

  • □ Know mutation patterns (JAK2, CALR, MPL)

  • □ Understand EPO levels

  • □ Recognise hallmark symptoms

  • □ Identify blood film clues

  • □ Practise regularly via Start a mock test


Practical examples / mini-cases

Case: A 60-year-old man presents with fatigue and abdominal fullness. Examination reveals massive splenomegaly. Blood film shows tear-drop cells.

Question: What is the most likely diagnosis?

Answer: Primary myelofibrosis

Explanation: Tear-drop red cells (dacrocytes) and massive splenomegaly are classic for myelofibrosis due to marrow fibrosis and extramedullary haematopoiesis.


Medical student revising haematology notes for MRCP Part 1 exam preparation on myeloproliferative disorders

Common pitfalls (5 bullets)

  • Confusing secondary erythrocytosis with PV

  • Ignoring erythropoietin levels

  • Forgetting CALR mutations in JAK2-negative disease

  • Overlooking bleeding risk in ET

  • Missing tear-drop cells as a diagnostic clue


FAQs

1. What is the most important mutation in MPNs?

JAK2 V617F is the most important mutation, especially in PV, and is frequently tested in MRCP Part 1.

2. How is PV distinguished from secondary polycythaemia?

PV has low erythropoietin levels, whereas secondary causes have elevated EPO due to hypoxia or other stimuli.

3. Why can ET cause bleeding despite high platelets?

Platelet dysfunction leads to ineffective clotting despite increased platelet numbers.

4. What is the hallmark of myelofibrosis on blood film?

Tear-drop (dacrocyte) red cells are a classic and highly testable feature.

5. Which MPN has the poorest prognosis?

Primary myelofibrosis generally carries the worst prognosis due to marrow failure and AML transformation risk.


Ready to start?

Consolidate your understanding of haematology topics with the MRCP Part 1 overview and sharpen exam performance using Free MRCP MCQs. For realistic exam conditions, attempt a Start a mock test today.


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