Morphology and cytochemistry of acute leukemia – cytochemical reactions
Blasts in acute myeloblastic leukemia are usually large cells with a round or irregularly shaped nucleus. A pathognomonic morphological marker of acute myeloblastic leukemia is the detection of granules or linear azurophilic granularity (Auer sticks) in the cytoplasm of blast cells.
Most forms of acute myeloblastic leukemia, unlike acute lymphoblastic leukemia, can be morphologically identified. Myeloblasts are divided into types depending on the number and quality of granules (in type I blasts there are no granules; type II blasts contain up to 15 delicate granules; in type III blasts, there are a lot of azurophilic granules).
Lymphoblasts are usually small, the core of a more regular form, the cytoplasm is scanty and agranular.
The essence of cytochemical research is to identify in the cell enzymes and cytoplasmic inclusions characteristic of a particular cell type. During the cytochemical reaction, an enzyme or other substance in the cell interacts with the working solution reagents.
The main cytochemical reactions used for the diagnosis and differential diagnosis of acute leukemia:
1) the most important detection of myeloperoxidase (the enzyme azurophilic granules of cells of granulocyte and monocyte series); this reaction may be positive in the absence of visible granules;
2) the second most significant is Sudan black B; if one of the two reactions is positive in more than 3% of blasts, this indicates that they belong to the myeloid line;
3) nonspecific esterase is typical for monocytes and monoblasts, but can be detected in acute lymphoblastic leukemia and MH; these reactions are sensitive to sodium fluoride inhibition, which is used for differential diagnosis;
4) positive PAS-reaction indicates the presence of glycogen in the cells and is most typical for acute erythromyelosis; glycogen is also detected in acute lymphoblastic leukemia and other types of acute myeloblastic leukemia
5) naphthol AS-D chloroacetate esterase is found in the maturing myeloid cells;
6) acid phosphatase is detected at T-ALL;
7) a-naphtholbutyrateterase indicates monocytic differentiation of cells.
Other methods are used to verify the variant of acute leukemia. So, for the diagnosis of M4 and M5 variants of acute myeloblastic leukemia, a cytobacterial lysozyme test is used.