What is Myeloproliferative Neoplasm?

Myeloproliferative Neoplasms: Understanding the Disease

Myeloproliferative neoplasms (MPNs) are a rare group of diseases with relatively low incidence rates. Many people are unfamiliar with what MPNs entail. Essentially, MPNs arise from the excessive growth of bone marrow cells. The bone marrow's primary function is hematopoiesis, and the development of MPNs leads to various blood disorders due to impaired blood production, posing significant health risks.

Clinically, MPNs are categorized into four types based on the predominant cell line proliferation:

1. Polycythemia Vera (PV): Characterized by the proliferation of erythroid cells.
2. Chronic Myeloid Leukemia (CML): Predominantly involving granulocyte proliferation.
3. Essential Thrombocythemia (ET): Featuring megakaryocytic cell line proliferation.
4. Primary Myelofibrosis (PMF): Marked by fibroblast proliferation.

The etiology of these disorders remains unclear, with a higher prevalence among middle-aged and elderly individuals. CML is a type of leukemia, while the following three conditions are distinct entities.

Polycythemia Vera: Involves a significantly elevated total red blood cell mass, commonly known as polycythemia. Approximately 30% of patients develop bone marrow fibrosis, ultimately leading to marrow failure. Around 10% progress to acute leukemia. Symptoms include headaches, dizziness due to increased red blood cells and blood viscosity, bleeding, and thrombosis. Elevated blood pressure, splenomegaly, and increased peripheral hemoglobin levels (18-23 g/dL; hematocrit 55%-80%) are also observed. Diagnosis is confirmed by isotopic measurements indicating increased red cell mass (≥36 mL/kg for males, ≥32 mL/kg for females), with a blood oxygen saturation >92%, excluding other causes of secondary polycythemia.

Treatments such as radionuclide phosphorus, hydroxyurea, and busulfan have shown significant efficacy, providing convenient and effective symptomatic relief.

Essential Thrombocythemia: Characterized by a marked increase in platelet count, accompanied by bleeding or thrombosis. The male-to-female incidence ratio is 2:1. Approximately 8% of patients develop bone marrow fibrosis, and 10% progress to acute leukemia. The disease progresses slowly, with possible splenomegaly and consistently elevated platelet counts exceeding 600 × 10⁹/L. Platelet adhesion, aggregation, and third factor function may be reduced. For patients with bleeding complications, apheresis can rapidly reduce excessive platelet levels. Hydroxyurea, busulfan, or phosphorus-32 offer satisfactory therapeutic outcomes.

Primary Myelofibrosis: A disease characterized by diffuse fibrous tissue proliferation in the bone marrow, accompanied by extramedullary hematopoiesis (or myeloid metaplasia), primarily affecting the spleen, liver, and lymph nodes. Myeloid metaplasia is generally considered a manifestation of bone marrow proliferation rather than a compensatory response to fibrosis. This disease is insidious, with a course that can extend over 10 years. Progressive splenomegaly is a prominent feature, sometimes occupying the entire abdomen. Due to extramedullary hematopoiesis, peripheral blood may contain immature erythroid cells, immature granulocytes, and tear-drop-shaped red cells. Fibrosis makes bone marrow aspiration difficult, often resulting in "dry tap." Diagnosis is confirmed through bone marrow biopsy. While there is no cure, symptomatic and supportive treatments are the mainstay. Splenectomy may be considered for massive splenomegaly with compression symptoms, hyperfunction, or rupture. Calcitriol (1,25(OH)₂D₃) therapy shows some efficacy in fibrosis but requires monitoring for hypercalcemia. The most common causes of death include bone marrow failure or unrelated conditions such as cardiovascular diseases. Approximately 10-20% of patients eventually develop acute leukemia.