Myelodysplastic syndrome laboratory findings
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Nawal Muazam M.D.[2]
Overview
Laboratory Findings
Abnormalities include:
- neutropenia, anemia and thrombocytopenia (low cell counts of white and red blood cells, and platelets, respectively)
- abnormal granules in cells, abnormal nuclear shape and size
- chromosomal abnormalities, including chromosomal translocations and abnormal chromosome number.
- Full blood count and examination of blood film. The blood film morphology can provide clues about hemolytic anemia, clumping of the platelets leading to spurious thrombocytopenia, or leukemia.
- Blood tests to eliminate other common causes of cytopenias, such as lupus, hepatitis, B12, folate, or other vitamin deficiencies, renal failure or heart failure, HIV, hemolytic anemia, monoclonal gammopathy. Age-appropriate cancer screening should be considered for all anemic patients.
PAS stain
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
- Hypersegmented neutrophils (also seen in Vit B12/Folate deficiency)
- Hyposegmented neutrophils (Pseudo-Pelger Huet)
- Hypogranular neutrophils or pseudo Chediak Higashi large granules
- Dimorphic granules (basophilic and eosinophilic granules) within eosinophils
- Erythroid series
- Binucleated erythroid percursors and karyorrhexis
- Erythroid nuclear budding
- Erythroid nuclear strings or internuclear bridging (also seen in congenital dyserythropoietic anemias)
- 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)
- 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)
- Hyposegmented nuclear features in platelet producing megakaryocytes (lack of lobation)
- Hypersegmented (osteoclastic appearing) megakaryocytes
- Ballooning of the platelets (seen with interference contrast microscopy)
Other stains can help in special cases (PAS and napthol ASD chloroacetate esterase positivity) in eosinophils is a marker of abnormality seen in chronic eosinophilic leukemia and is a sign of aberrancy.
MDS can appear a lot like megaloblastic anemia however megaloblastic anemia has cell lysis thereby causing an increase in the bilirubin and LDH whereas, in MDS, these aren't elevated.
On the bone marrow biopsy high grade dysplasia (RAEB-I and RAEB-II) may show atypical localization of immature precursors (ALIPs) which are islands of immature cells/(blasts) clustering together. This morphology can be difficult to recognize 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. ALIP is thought to be a preleukemic harbinger and associated with a poor outcome in RA and RARS.
Hypoplastic MDS has a cellularity of less than 25-30% and shares features that appear to overlap with aplastic anemia and paroxysmal nocturnal hemoglobinuria (PNH). In these patients the administration of anti-thymocyte globulin (ATG) and cyclosporine have produced response rates of 44% and 84% respectively. The presence of a PNH clone, bone marrow hypocellularity and <5% bone marrow blasts are positive predictors of response to immunomodulation.
Malfunctions can occur in the cells of MDS patients. These can manifest as poor platelet aggregation or impaired neutrophil chemotaxis. One of the more phenotypically obvious acquired red blood cell disorders in MDS is alpha thalassemia which is usually associated with a microcytic and hypochromic erythrocyte indices and with somatic point mutation in ATRX, a chromatin remodeling factor encoded by the X-chromosome.
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 dyserthropoietic anemia (CDA I through IV) has been recognized, Pearson's syndrome (sideroblastic anemia), Jacobson's syndrome, ALA (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).