On the bone-marrow biopsy, high-grade dysplasia (RAEB-I and RAEB-II) may show atypical localization of immature precursors, which are islands of immature precursors cells (myeloblasts and promyelocytes) localized to the center of the intertrabecular space rather than adjacent to the trabeculae or surrounding arterioles. This morphology can be difficult to differentiate from treated leukemia and recovering immature normal marrow elements. Also, topographic alteration of the nucleated erythroid cells can be seen in early myelodysplasia (RA and RARS), where normoblasts are seen next to bony trabeculae instead of forming normal interstitially placed erythroid islands. Differential diagnosis
Myelodysplasia is a diagnosis of exclusion and must be made after proper determination of iron stores, vitamin deficiencies, and nutrient deficiencies are ruled out. Also, congenital diseases such as congenital dyserythropoietic anemia (CDA I through IV) have been recognized, Pearsons syndrome (sideroblastic anemia), Jordans anomaly – vacuolization in all cell lines may be seen in Chanarin-Dorfman syndrome, aminolevulinic acid enzyme deficiency and other more esoteric enzyme deficiencies are known to give a pseudomyelodysplastic picture in one of the cell lines; however, all three cell lines are never morphologically dysplastic in these entities with the exception of chloramphenicol, arsenic toxicity, and other poisons.All of these conditions are characterized by abnormalities in the production of one or more of the cellular components of blood (red cells, white cells other than lymphocytes, and platelets or their progenitor cells, megakaryocytes).
The International Prognostic Scoring System is another tool for determining the prognosis of MDS, published in Blood in 1997. This system takes into account the percentage of blasts in the marrow, cytogenetics, and number of cytopenias. Genetic markers
Although not yet formally incorporated in the generally accepted classification systems, molecular profiling of myelodysplastic syndrome genomes has increased the understanding of prognostic molecular factors for this disease. For example, in low-risk MDS, IDH1 and IDH2 mutations are associated with significantly worsened survival. Epidemiology
The exact number of people with MDS is not known because it can go undiagnosed and no tracking of the syndrome is mandated. Some estimates are on the order of 10,000 to 20,000 new cases each year in the United States alone. The number of new cases each year is probably increasing as the average age of the population increases, and some authors propose that the number of new cases in those over 70 may be as high as 15 per 100,000 per year.The typical age at diagnosis of MDS is between 60 and 75 years; a few people are younger than 50, and diagnoses are rare in children. Males are slightly more commonly affected than females. History
Since the early 20th century, some people with acute myelogenous leukemia were begun to be recognized to have a preceding period of anemia and abnormal blood cell production. These conditions were lumped together with other diseases under the term "refractory anemia". The first description of "preleukemia" as a specific entity was published in 1953 by Block et al.