Mechanism of development and classification
Acute leukemias belong to the group of hemoblastosis. The basis of pathogenesis is a mutation in the genetic apparatus of a hematopoietic cell. Under the action of triggers (radiation, benzene, cytostatics, viruses, e.g., Epstein–Barr virus), normal regulatory genes (proto-oncogenes) become oncogenes. A tumor clone of blast cells is formed. They rapidly multiply in the bone marrow, displacing normal hematopoietic lineages.
Depending on the type of progenitor cells, acute leukemias are divided into two large groups:
- Lymphoblastic leukemias. The substrate is low-differentiated lymphocyte precursors.
- Non-lymphoblastic (myeloid) leukemias. This includes myeloblastic, myelomonoblastic, monoblastic, erythroleukemia, and megakaryoblastic leukemias.
Clinical presentation
Symptoms of the disease develop rapidly and depend little on the specific morphological cell type. Several leading syndromes are distinguished in the clinical picture:
- General toxic and anemia: weakness, high fever, loss of appetite, pallor, and other signs of anemia.
- Immunodeficiency and infections: development of severe necrotic tonsillitis, ulcerative stomatitis, and secondary infections.
- Hemorrhagic syndrome: bleeding that occurs due to a critical drop in the platelet count.
- Tumor infiltration syndrome: bone and joint pain, enlargement of the liver and spleen (in late stages). Acute lymphoblastic leukemia is also characterized by lymphadenopathy.
Laboratory diagnostics
Acute leukemia can be suspected already from the complete blood count (CBC), but the final diagnosis is made only after bone marrow examination.
Changes in peripheral blood:
- Progressive anemia with a decreased reticulocyte count.
- Thrombocytopenia.
- The leukocyte count may be decreased, normal, or moderately elevated.
- “Leukemic gap” (hiatus leukemicus) — a key sign. Blast cells (more than 10–20%) and mature forms are found in the blood smear, but intermediate stages of maturation are completely absent.
Bone marrow examination: To confirm the diagnosis, sternal puncture or iliac bone trephine biopsy (considered more informative) is performed. The main criterion is an abundance of blast cells. The exact variant of leukemia is established using cytochemical analysis and immunophenotyping.
Principles of treatment
The basis of treatment is chemotherapy. Cytostatics (e.g., cytarabine) are used to destroy tumor cells (cytolysis). Achieving remission takes about 4–6 weeks. Subsequently, long-term maintenance therapy (at least 3 years) using factors stimulating hematopoiesis is required.
Additionally, supportive care is administered: platelet transfusion for bleeding and antibiotics (gentamicin, etc.) to combat infections.
Massive cell destruction during chemotherapy can cause tumor lysis syndrome: purines are released from destroyed cells, leading to an excess of uric acid and symptoms resembling gout.
Briefly: answers to topical questions
What cytochemical reactions are used to accurately determine the variant of acute leukemia?
To verify the variant of acute leukemia (using acute promyelocytic leukemia as an example), reactions for enzymes and lipids are used. The following specific cytochemical reactions are distinguished to identify tumor cells:
- Myeloperoxidase reaction (MPO) — a classic sign, showing a very pronounced reaction.
- Lipid stain (Sudan Black B, SBB) — Sudan Black staining to detect lipid inclusions.
- Chloroacetate esterase reaction — also characterized by a very pronounced reaction.
What exact percentage of blast cells in the bone marrow is the criterion for the diagnosis of acute leukemia?
The key criterion for diagnosing acute leukemia during bone marrow examination is the detection of more than 25% blast cells. Depending on the form of the disease, this indicator may vary:
- Acute lymphoblastic leukemia — the content of immature cells in the myelogram often exceeds 90%.
Additionally, general hypercellularity and pronounced suppression of other healthy hematopoietic lineages are noted in the bone marrow.
Remember the essence of the “leukemic gap” (hiatus leukemicus): there are “children” (blasts) and “elders” (mature cells) in the blood, but no “adults” (intermediate forms).
Class and exam questions
How does acute leukemia differ from chronic leukemia?
In acute leukemia, the tumor consists of young, blast (non-maturing) cells. In chronic leukemia, it consists of maturing and mature cells.
What is a “leukemic gap”?
This is a specific sign of acute leukemia in a blood test when blast cells and mature elements are present, but intermediate maturation stages are absent.
Why do tonsillitis and bleeding occur in leukemia?
Tumor cells displace normal hematopoietic lineages in the bone marrow. A shortage of normal leukocytes leads to severe infections (tonsillitis), and a deficiency of platelets leads to bleeding.
What else to study on this topic
- Mechanism of proto-oncogene transformation into oncogenes
- Features of acute lymphoblastic leukemia
- Types of non-lymphoblastic (myeloid) leukemias
- Cytochemical and immunophenotypic examination of the bone marrow
- Tumor lysis syndrome: pathogenesis and prevention
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