What Are MPN and MDS?

  • Myeloproliferative Neoplasms (MPNs) are blood disorders where the bone marrow produces too many mature blood cells—this could be red cells, white cells, or platelets.

  • Myelodysplastic Neoplasms (MDS) are disorders where the bone marrow produces abnormal (dysplastic) blood cells that die early, leading to ineffective hematopoiesis and low cell counts in blood.

Even though the term has changed from “Myelodysplastic Syndrome” to “Myelodysplastic Neoplasm,” the abbreviation remains MDS.

Pathophysiology: Proliferation vs Ineffectiveness

  • MPNs are proliferative disorders—there is an increase in the number of mature, functional blood cells. Dysplasia is absent.

  • MDS is characterized by dysplasia and apoptosis. Blood cell production is ineffective, and immature cells often die before reaching the peripheral blood.

To diagnose MDS, at least 10% of the cells in one cell lineage (erythroid, myeloid, or megakaryocytic) must show dysplastic changes.

Types of Diseases Under Each Category

Myeloproliferative Neoplasms (MPN)

  • Chronic Myeloid Leukemia (CML)

  • Polycythemia Vera

  • Essential Thrombocythemia

  • Juvenile Myelomonocytic Leukemia

Myelodysplastic Neoplasms (MDS)

  • MDS with ring sideroblasts

  • MDS with excess blasts

  • MDS with isolated genetic abnormalities (e.g., 5q deletion)

There are also overlap syndromes that show features of both MPN and MDS, called MDS/MPN overlap disorders.

Risk Factors

  • MPNs: Radiation exposure, rarely genetic predisposition

  • MDS: Past chemotherapy, radiation therapy, or benzene exposure

Genetic Mutations

MPN Mutations

  • BCR-ABL in CML

  • JAK2 in Polycythemia Vera

  • CALR and MPL in Essential Thrombocythemia

  • RAS in Juvenile Myelomonocytic Leukemia

MDS Mutations

  • 5q deletion

  • SF3B1 mutation

  • TP53 inactivation

Cell Lineage Involvement

  • In MPNs, typically one cell lineage is predominantly affected. For example:

    • Erythroid → Polycythemia Vera

    • Myeloid → CML

    • Megakaryocytic → Essential Thrombocythemia

  • In MDS, multiple lineages are often affected, and all show dysplasia.

Blood and Bone Marrow Findings

MPNs

  • Peripheral Blood: High counts (cytosis) with mature cells

  • Bone Marrow: Hypercellular with effective hematopoiesis

  • Cell Maturity: Cells are mature and functional

MDS

  • Peripheral Blood: Low counts (cytopenia) with dysplastic cells

  • Bone Marrow: Hypercellular but with ineffective hematopoiesis

  • Cell Maturity: Cells are often immature or dysplastic

Dysplastic Features in MDS

Erythroid Lineage

  • Ring sideroblasts (visible with iron stain)

  • Megaloblastoid maturation

  • Cytoplasmic vacuoles

  • Cytoplasmic and nuclear bridging

  • Binucleation or multinucleation

Myeloid Lineage

  • Hypogranular neutrophils

  • Pseudo-Pelger-Huët anomaly (bilobed neutrophils)

  • Abnormal nuclear shapes

  • Cytoplasmic vacuolation

Megakaryocytic Lineage

  • Pawn ball megakaryocytes (separated nuclei)

  • Cloud-like or smudged nuclei

Clinical Presentation

MPN

  • Thrombosis

  • Splenomegaly

  • Hyperviscosity

  • Usually asymptomatic until complications

MDS

  • Fatigue (due to anemia)

  • Bleeding (due to low platelets)

  • Infections (due to neutropenia)

Risk of Progression

  • MPNs usually progress to myelofibrosis and rarely to acute myeloid leukemia (AML).

  • MDS has a higher risk of progressing to AML, especially in cases with excess blasts.

Treatment Strategies

MPN

  • Cytoreductive therapy

  • JAK inhibitors

  • Phlebotomy (in Polycythemia Vera)

MDS

  • Supportive care (anemia, infections, bleeding)

  • Hypomethylating agents

  • Stem cell transplantation (curative option)

Prognosis

  • MPNs generally have a better prognosis than MDS. However, complications like myelofibrosis or leukemic transformation can occur over time.

  • MDS has a poorer prognosis, especially when associated with excess blasts or high-risk genetic mutations.

Final Summary

Think of it this way:
🔹 MPN = Proliferation of mature cells, effective production, high counts
🔹 MDS = Dysplasia of immature cells, ineffective production, low counts

If you found this post helpful and want to learn visually, you can watch the full explanation on our YouTube channel.

👉 Watch here:

Download the PDF 
If you’d like to review this topic offline you can download the PDF version of this content here:
👉 Click to Download: MPN vs MDS Summary (PDF)