Myelodysplastic Syndromes (MDS)

Definition

The myelodysplastic syndromes (MDS, formerly known as "preleukemia") are a diverse collection of hematological conditions united by ineffective production of blood cells and varying risks of transformation to acute myelogenous leukemia (AML).

Myelodysplastic syndromes (MDS) are bone marrow stem cell disorders resulting in disorderly and ineffective hematopoiesis (blood production) manifested by irreversible quantitative and qualitative defects in hematopoietic (blood-forming) cells. In a majority of cases, the course of disease is chronic with gradually worsening cytopenias due to progressive bone marrow failure. Approximately one-third of patients with MDS progress to AML within months to a few years.

Sample Cases

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Epidemiology

The median age at diagnosis of a MDS is between 60 and 75 years; a few patients are less than 50; MDS are rare in children. Males are slightly more commonly affected than females. Signs and symptoms are nonspecific and generally related to the blood cytopenias. Some estimates are on the order of 10,000 to 20,000 new cases each year in the United States alone. The incidence is probably increasing as the age of the population increases, and some authors propose that the incidence in patients over 70 may be as high as 15 cases per 100,000 per year.

Although there is some risk for developing acute myelogenous leukemia, about 50% of deaths occur as a result of bleeding or infection. Leukemia that occurs as a result of myelodysplasia is notoriously resistant to treatment.

Possible causes

MDS is caused by environmental exposures such as radiation and benzene; other risk factors have been reported inconsistently. Secondary MDS occurs as a late toxicity of cancer treatment, usually with a combination of radiation and the radiomimetic alkylating agents such as busulfan, nitrosourea, or procarbazine (with a latent period of 5 to 7 years) or the DNA topoisomerase inhibitors (2 years). Both acquired aplastic anemia following immunosuppressive treatment and Fanconi's anemia can evolve into MDS.

Morphology

Dysplasia can affect all three lineages seen in the bone marrow. The best way to diagnose dysplasia is by morphology and special stains (PAS) used on the bone marrow aspirate and peripheral blood smear. Dysplasia in the myeloid series is defined by:

• Granulocytic series
  1. Hypersegmented neutrophils (also seen in Vit B12/Folate deficiency)
  2. Hyposegmented neutrophils (Pseudo-Pelger Huet)
  3. Hypogranular neutrophils or pseudo Chediak Higashi large granules
  4. Dimorphic granules (basophilic and eosinophilic granules) within eosinophils
• Erythroid series
  1. Binucleated erythroid percursors and karyorrhexis
  2. Erythroid nuclear budding
  3. Erythroid nuclear strings or internuclear bridging (also seen in congenital dyserythropoietic anemias)
  4. PAS (globular in vacuoles or diffuse cytoplasmic staining) within erythroid precursors in the bone marrow aspirate (has no bearing on paraffin fixed bone marrow biopsy). Note: One can see PAS vacuolar positivity in L1 and L2 blasts (AFB classification; the L1 and L2 nomenclature is not used in the WHO classification)
  5. Ringed sideroblasts seen on Prussian blue iron stain (10 or more iron granules encircling 1/3 or more of the nucleus and >15% ringed sideroblasts when counted amongst red cell precursors)
• Megakaryocytic series (can be the most subjective)
  1. Hyposegmented nuclear features in platelet producing megakaryocytes (lack of lobation)
  2. Hypersegmented (osteoclastic appearing) megakaryocytes
  3. Ballooning of the platelets (seen with interference contrast microscopy)

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