Key features that almost all MDS patients share are a macrocytic anemia that is refractory, cytopenias of one or more cell lines, and a hypercellular marrow. Organomegaly is not a frequent finding. The symp toms that patients experience—weakness, infection, and easy bruisability—are all explained from the perspective of the clonal abnormality, depending on which cell line is the most affected. The following is a likely sequence of events:
• Weakness develops from the anemia and shortened red cell survival.
• Infections develop due to white blood cells with poor microbicidal activity and decreased chemotaxis.
• Bruising develops due to lower numbers and abnormally functioning platelets.
In general, a diagnosis of MDS is made based on the percentage of blasts present, the type of dysplasia seen in the marrow and the peripheral smear, and the presence or absence of ringed sideroblasts (see Chapter 5). Classification into one of the six subtypes of MDS is made once all of the information from marrow, peripheral smear, cytogenetic studies, and immunologi-cal features is gathered.
Dysplasia in the bone marrow and peripheral smear are hallmark features of the MDSs. Therefore, it is essential that the morphologist have an understanding of what is meant by this term with respect to variations in each cell line. Well-stained and well-distributed peripheral smears and bone marrow preparations are an essential ingredient to determining if dysplasia is present in the individual. Their importance cannot be underestimated. By definition, dysplasia means "abnormal development of tissue." In the bone marrow, this may manifest itself in the nuclear and cytoplasmic characteristics of precursor cells. Bone marrow nuclear changes may include multinuclearity, disintegration of the nucleus, asynchrony similar to megaloblastic changes, and nuclear bridging between cells. Bone marrow cytoplasmic changes include vacuolization or poor granulation. In the peripheral smear, similar changes may be seen like hypogranulated cells (Fig. 14.1), hypergranu-lated cells, hyposegmented cells, nuclear material that is too smooth, pseudo-Pelger-Huet cells, and red cell size changes (Fig. 14.2). Platelet abnormalities in the peripheral smear include abnormal size (Fig. 14.3), or megakaryocytic fragments. Degenerating neutrophils may also be seen (Fig 14.4). What usually comes to mind when these peripheral smear changes are first observed are technical factors like a poorly stained smear or a poorly made smear. The morphologist may not exercise the index of suspicion, feeling that what is
Figure 14.3 Giant platelet.
observed is not hematologically relevant. Yet when 10%6 of a particular cell line starts manifesting any of the changes noted, the change is significant and due to a pathology (Table 14.1).
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