Difference between revisions of "Acute myeloid leukaemia"
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Revision as of 10:42, 26 March 2020
Morphology forms of blood does not allow AML to be classified without additional samples and tests. However, when describing blasts on blood films it is helpful to try and ascribe the cells to a morphological type, since these criteria still form the basis of division when other class-defining features (genetic or cytogenetic) are not found (AML not otherwise classified).
AML with minimal differentiation (FAB M0)
Major features: Blasts cells have medium size with the typical diffuse chromatin pattern of a blast cell. Nuclei may be round, angular or indented (usually with one or more visible nucleoli). Cytoplasm is agranular; the degree of cytoplasmic basophilia may vary between cases.
Other aspects: The cells may resemble lymphoblasts with “L2” morphology – for example having cytoplasmic vacuoles, so immunophenotyping is very important to clearly establish lineage.
AML without maturation (FAB M1)
Major features Most often this form of AML has blasts of medium size with basophilic cytoplasm. Up to 10% of cells may have indistinct granules, and Auer rods may be present.
Other aspects: This form of AML does not mature so very few mature cells will be present in the blood. It is useful also to look for signs of MDS in other lineages.
AML with maturation (FAB M2)
Major features of blast cells: Blast are medium sized with basophilic cytoplasm. The nucleus is primitive, and is most often offset because of the golgi body (visible as a pale area adjacent to the nucleus). Granulation may be indistinct or obvious and involves >10% of cells. The granules may coalesce and form one or more masses. and Auer rods are frequently present.
Acute promyelocytic leukaemia (FAB M3)
There are two forms of APL:
Hypergranular APL: The number of abnormal cells in blood is generally low and the blast cells vary greatly in size, and cytoplasm is densely packed by large granules that may obscure the nuclear appearance. In some cells rod-like structures may occur in bundles (basket cells). The cells differ from normal promyelocytes where Golgi zone is generally more obvious and the more uniform granules are dispersed.
Microgranular (hypogranular) APL: The blasts are often more numerous and have a very distinct appearance - most commonly a bilobed nucleus where the very soft chromatin makes the appearance almost transluscent. There is little or no granulation in most cells, although occasional hypergranular forms may be detected.
Other aspects: Look also for features of an associated coagulopathy which is caused by the contents of the abnormal granules and occurs in both forms of APL. In particular look for fragmented red cells and a disproportionate thrombocytopenia.
Acute myelomonocytic leukaemia (FAB M4)
Major features: The blast cells are large with abundant cytoplasm that may have variable basophilia. The appearance is mixed, with cells that have irregular nuclear shape and scattered granulation or Auer rods suggesting granulocytic maturation. Other cells have the appearance of more typical monoblasts with a round or folded nucleus that has lacy nuclear chromatin. The basophilic cytoplasm is abundant and may have fine azurophilic granules and vacuolation.
Other aspects: the M4eo variant has pronounced abnormal eosinophils and eosinphil precursors in marrow, but these may not appear in blood.
Acute monoblastic and monocytic leukaemia
Monoblastic (FAB M5a)
Monocytic (FAB M5b)
Major features: Monoblasts can be distinguished by having a roughly circular nucleus, delicate lacy chromatin, and abundant, often basophilic cytoplasm. These cells may also have pseudopods. By contrast, promonocytes have a more convoluted nucleus, and their cytoplasm may contain metachromatic granules.
Other aspects: This form of AML may have very high circulating blast cell counts with infiltration of tissues and a coagulopathy may be seen. The appearances of cells in marrow or blood may differ with cells in blood appearing more mature. The translocation t[11q23] may be more frequently seen in this form of AML.
Acute erythroid leukaemia (FAB M6)
Major features The blast cells have nuclei that are usually round, but may be irregular with lobulation, and cytoplasm may or may not show the basophilia associated with earier erythroid forms although this is by no means always the case.
Other aspects: These are usually distinctive: red cells that maturing from the leukemic erythroblasts frequently being bizarre with dysplastic features that include: megaloblastic and giant forms, multinucleated cells, cytoplasmic vacuolation. Cytoplasmic blebs that resemble megakaryocytic leukemia may occur.
Acute megakaryoblastic leukaemia (FAB M7)
Major features: Medium to large-sized blasts. Typically the nucleus is round (or occasionally indented) with one or more nucleoli, and may have the high nucleocytoplasmic ratio typical of lymphoblasts. The cytoplasm is agranular and generally basophilic, and may show pseudopod formation.
Other aspects: There may be circulating micromegakaryocytes, megakaryoblast fragments, dysplastic large platelets, and hypogranular neutrophils.
Acute basophilic leukaemia