Which morphologic features are characteristic of unclassifiable myelodysplastic syndromes (MDS-U)?

Updated: Jul 21, 2020
  • Author: Robert P Hasserjian, MD; Chief Editor: Christine G Roth, MD  more...
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Answer

Answer

Morphologic dysplasia in at least one lineage characterizes most types of unclassifiable myelodysplastic syndromes (MDS-U); cases with morphologic dysplasia are placed into the MDS-U category if they have discordant cytopenias (pancytopenia with dysplasia limited to one lineage) or peripheral blood blast count (1% blasts in the peripheral blood with no increase in blasts in the bone marrow) (see the images below).

Pathology of unclassifiable myelodysplastic syndro Pathology of unclassifiable myelodysplastic syndromes (MDS-U). Bone marrow biopsy section from a patient with myelodysplastic syndrome, unclassifiable (MDS-U) (pancytopenia and -7 cytogenetic abnormality). The biopsy is hypocellular with hemosiderin deposition secondary to multiple transfusions. Megakaryocytes are not dysplastic.
Pathology of unclassifiable myelodysplastic syndro Pathology of unclassifiable myelodysplastic syndromes (MDS-U). Bone marrow aspirate smear from a patient with myelodysplastic syndrome, unclassifiable (MDS-U) (pancytopenia and -7 cytogenetic abnormality). Occasional late mitotic figures in erythroid elements are present, but no significant erythroid or myeloid dysplasia exists.

In the latter case, examining well-prepared peripheral smears and obtaining an accurate blast count on at least 200 cells in the peripheral smear is important; in smears with marked leukopenia, examination of a concentrated buffy coat may be helpful in ensuring sufficient cells to perform an accurate count. [9] The possibility that the marrow aspirate may be hemodilute and the case actually represents myelodysplastic syndrome with excess blasts -1 or -2  with a nonrepresentative aspirate should be considered.

Cases with cytopenias that appear to lack significant morphologic dysplasia but bear a myelodysplastic syndrome (MDS)–defining cytogenetic abnormality should undergo careful examination of aspirate smears, peripheral blood, and bone marrow biopsy (the latter for megakaryocyte morphology, ideally examining at least 30 megakaryocytes) to ensure that morphologic dysplasia is not present in at least 10% of any lineage. Note that cases with a single cytopenia and dysplasia in a single but different lineage (such as anemia with dysplasia limited to the megakaryocytic lineage) are not classified as MDS-U; these cases are still considered within the spectrum of refractory cytopenia with unilineage dysplasia (RCUD).

In all cases of MDS-U the possibility of a myeloproliferative neoplasm (MPN) or myelodysplastic/myeloproliferative overlap neoplasm (MDS/MPN) should be excluded. [10] The presence of persistent peripheral blood monocytosis (> 1 x 109/L), thrombocytosis (≥ 450 x 109/L), or leukocytosis (≥ 13 x 109/L) in a case in which MDS-U is considered should be placed in the MDS/MPN category. Cases that exhibit "proliferative-type" megakaryocyte morphology (enlarged, hyperlobated, and hyperchromatic megakaryocytes), splenomegaly, and bone marrow fibrosis may represent cases of primary myelofibrosis, mimicking MDS due to cytopenias and even morphologic dysplasia of neutrophils and erythroid elements that may occur in the later stages of disease.


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