Modern differential diagnosis of acute leukemia variants

The polymorphism of leukemic elements in acute leukemia is pronounced significantly. The presented schematic description of the signs of cells of different types does not include the whole variety of forms, therefore the differential diagnosis of disease variants can cause certain difficulties. Differences in the diagnosis of three morphologists in the study of the same observations can be 5-10%.

One of the most difficult diagnostic options for acute non-lymphoblastic leukemia is myeloblastic with minimal differentiation. It was singled out by the authors of the FAB classification among the latter. This variant of leukemia has to be differentiated from acute lymphoblastic, megakaryoblastic, bi-phenotypic, and true erythroid leukemias.

The difference between M0 and acute lymphoblastic leukemia and large cell lymphoma in the leukemization stage lies in the expression of myeloid (CD33, CD13) and the absence of lymphoid antigens. PAS-positive substance is more often defined in diffuse, but not in granular form.

In the differential diagnosis of MO variants from M6 and M7, the criterion is the absence of specific immunological markers of the erythroid (GlyA) and megakaryocytic (CD41, CD61) series. In contrast to biphenotypic leukemia, only myeloid antigens are detected on blasts and lymphoid antigens are absent.

In myeloblastic leukemia without maturation, two types of blasts can occur. In blasts of type I, a large nucleol is determined in the nucleus, primary granules are absent, the nuclear-cytoplasmic ratio is high. For blasts of type II, small nucleols are characteristic, the presence in the cytoplasm of several primary granules, a moderate nuclear-cytoplasmic ratio. Acute myeloid leukemia with type I blasts with a low peroxidase content (less than 10%) is differentiated from acute lymphoblaqueosis. In these cases, the data of immunophenotypic research, namely the expression of myeloid antigens CD33 and CD13, are very significant.

In type II myeloblasts, differential diagnosis is performed with the M2 variant. The presence in the bone marrow of less than 10% of ripening granulocytes gives grounds to establish the variant Ml, and not M2 of acute non-lymphoblastic leukemia.

Myeloblastic leukemia with maturation is heterogeneous in its characteristics. Blasts vary in size, number of forms with granularity, degree of disgranulopoiesis, cytogenetic parameters. Comparison of M2 patients with acute non-lymphoblastic leukemia with t (8; 21) and expression of the AML / ETO gene and the absence of this anomaly showed that in the former, compared to the latter in the bone marrow, Auer’s rods were more common, the peroxidase activity was higher, trophilia was determined by pink staining, the number of eosinophils was slightly increased (2–6%).

It should be noted that, on the basis of morphological parameters without data from the karyotype study, it is difficult to distinguish these groups of patients. The clinical course of leukemia with this translocation proceeded in patients more favorably than in its absence.