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Myelodysplastic syndrome (MDS) involves a group of disorders typified by peripheral cytopenia, dysplastic hematopoietic progenitors, a hypercellular bone marrow, and a high risk of conversion to acute myelocytic leukemia (AML). Symptoms are referable to the specific cell line most affected and may include fatigue, weakness, pallor (secondary to anemia), increased infections and fever (secondary to neutropenia), and increased bleeding and bruising (secondary to thrombocytopenia). Diagnosis is by blood count, peripheral smear, and bone marrow aspiration. Treatment with 5-azacytidine may help; if AML supervenes, it is treated per the usual protocols.
Pathophysiology
MDS is a group of disorders often referred to as preleukemia, refractory anemia, Philadelphia chromosome–negative chronic myelocytic leukemia, chronic myelomonocytic leukemia, or agnogenic myeloid metaplasia, resulting from a somatic mutation of hematopoietic precursors. Etiology is often unknown, but risk is increased with exposure to benzene, radiation, and chemotherapeutic agents (particularly long or intense regimens and those involving alkylating agents and epipodophyllotoxins).
MDS is characterized by clonal proliferation of hematopoietic cells, including erythroid, myeloid, and megakaryocytic forms. The bone marrow is normal or hypercellular, and ineffective hematopoiesis can cause anemia (most common), neutropenia, thrombocytopenia, or a combination. The disordered cell production is also associated with morphologic cellular abnormalities in bone marrow and blood. Extramedullary hematopoiesis may occur, leading to hepatomegaly and splenomegaly. Myelofibrosis is occasionally present at diagnosis or may develop during the course of MDS. Classification is by blood and bone marrow findings (see Table 4: Leukemias: Myelodysplastic Syndrome Bone Marrow Findings and Survival ). The MDS clone is unstable and tends to progress to AML.
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Table 4
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| Myelodysplastic Syndrome Bone Marrow Findings and Survival |
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Classification
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Criteria
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Median Survival (yr)
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Refractory anemia
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Anemia with reticulocytopenia
Normal or hypercellular marrow with erythroid hyperplasia and dyserythropoiesis
Blasts ≤ 5% of nucleated marrow cells (NMC)
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≥ 5
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Refractory anemia with sideroblasts
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Same as refractory anemia, but with ringed sideroblasts > 15% of NMC
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≥ 5
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Refractory anemia with excess blasts
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Some cytopenia of ≥ 2 cell lines with morphologic abnormalities of blood cells
Hypercellular marrow with dyserythropoiesis and dysgranulopoiesis
Blasts 5–20% of NMC
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1.5
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Chronic myelomonocytic leukemia
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Same as refractory anemia with excess blasts and absolute monocytosis in blood
Significant increase in marrow monocyte precursors
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1.5
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Refractory anemia with excess blasts in transformation
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Refractory anemia with excess blasts and ≥ 1 of the following:
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0.5
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NMC = nucleated marrow cells.
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Symptoms and Signs
Symptoms tend to reflect the most affected cell line and may include pallor, weakness, and fatigue (anemia); fever and infections (neutropenia); and increased bruising, petechiae, epistaxis, and mucosal bleeding (thrombocytopenia). Splenomegaly and hepatomegaly are common. Symptoms may also be referable to other underlying disorders; eg, in elderly patients with preexisting cardiovascular disorders, anemia from MDS may exacerbate anginal pain.
Diagnosis
MDS is suspected in patients (especially the elderly) with refractory anemia, leukopenia, or thrombocytopenia. Cytopenias secondary to congenital disorders, vitamin deficiencies, or drug adverse effects must be ruled out. Diagnosis is by examining peripheral blood and bone marrow and identifying morphologic abnormalities in 10 to 20% of cells of a particular lineage.
Anemia is the most common feature, associated usually with macrocytosis and anisocytosis. With automatic cell counters, these changes are indicated by an increased MCV and RBC distribution width. Some degree of thrombocytopenia is usual; on peripheral smear, platelets vary in size, and some appear hypogranular. The WBC count may be normal, increased, or decreased. Neutrophil cytoplasmic granularity is abnormal, with anisocytosis and variable numbers of granules. Eosinophils also may have abnormal granularity. Pseudo Pelger-Huët cells (hyposegmented neutrophils) may be seen. Monocytosis is characteristic of the chronic myelomonocytic leukemia subgroup, and immature myeloid cells may occur in the less well differentiated subgroups. The cytogenetic pattern is usually abnormal, with one or more clonal cytogenetic abnormalities often involving chromosomes 5 or 7.
Prognosis
Prognosis depends greatly on classification and on any associated disorder. Patients with refractory anemia or refractory anemia with ringed sideroblasts are less likely to progress to the more aggressive forms and may die of unrelated causes.
Treatment
Azacitidine relieves symptoms, decreases the rate of transformation to leukemia and the need for transfusions, and probably improves survival. Other therapy is supportive, including RBC transfusions as indicated, platelet transfusions for bleeding, and antibiotic therapy for bacterial infection. Deoxyazacitidine, a hypomethylating agent, is sometimes effective, even in patients who do not respond to azacitidine. In some patients, erythropoietin to support RBC needs, granulocyte colony-stimulating factor to manage severe symptomatic granulocytopenia, and, when available, thrombopoietin for severe thrombocytopenia can serve as important hematopoietic support but have not increased survival. Allogeneic stem cell transplantation is the treatment of choice for young patients, and nonablative allogeneic bone marrow transplantations are now being studied for patients > 50 yr. Response of MDS to chemotherapy, typically regimens similar to those used for AML, is similar to that of AML after age and karyotype are considered.
Key Points
Last full review/revision July 2012 by Michael E. Rytting
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