Acute erythromyelosis and erythroid leukemia (M6a and M6b according to the FAB classification) – diagnosis

Acute erythromyelosis and erythroid leukemia (M6a and M6b according to the FAB classification): • accounts for 5-6% of all acute non-lymphoblastic leukemia (ONLL);

1) acute erythromyelosis:

• in the bone marrow, erythroid progenitors account for more than 50% of all cells, myeloblasts, more than 20% of cells of the non-erythroid population;
• cells of the red row have pronounced signs of dysplasia: megaloblastoid changes, dissociation of nuclear maturation and cytoplasm, uneven staining of the cytoplasm, the presence of Jolly bodies, multi-core forms. They increase the number of siderophilic granules, determine the positive PAS-reaction in diffuse and / or granular form;
• erythroid progenitors react with ICA to glycophorin A and hemoglobin A;
• myeloblasts contain granularity, single Auer sticks, are positive in reactions to peroxidase, ASD-chloroacetate esterase and lipids;
• blasts express myeloid lineage antigens CD13, CD33, CD117, and also sometimes CD34 and HLA-DR, react with MCA to peroxidase;

2) erythroid leukemia:

• the blast population prevails in the bone marrow (more than 80%);
• blasts of medium or large size with rounded nuclei, delicate chromatin structure and 1–2 nucleoli, cytoplasm basophilic, without grain, sometimes contains vacuoles;
• blasts do not have myeloperoxidase, lipids, contain granules of PAS-positive substance, nonspecific esterase, acid phosphatase;
• there are no myeloid immunological markers in blasts, early forms express CD36, more mature erythroid glycophorin A antigen;
• Multiple chromosomal rearrangements are detected, often involving chromosomes 5 and 7.