Leukemia-like, is a state, not a specific type of disease. As the name implies, it is a manifestation of a marked increase in the total number of white blood cells in the peripheral blood, as in leukemia.
The key difference from “leukemia” is that the increased leukocytes are intermediate and late stage cells that are nearing maturity and are a protective response to some other disease or abnormal state; the increased cells in leukemia are derived from malignant clonal proliferation of primitive and early hematopoietic stem cells.
Like leukemias are more common in children and adolescents, with no difference in incidence between men and women.
The main causes of “leukoid” reactions are more severe infections, poisoning, malignancy, hemorrhage, acute hemolysis, anaphylaxis, and history of drug use.
Infection
Common pathogens include bacteria, spirochetes, protozoa, and viruses, leading to different subtypes, with the neutrophilic type being the most common.
- Granulocytic type: Commonly seen in severe infectious diseases such as pneumonia, meningitis, diphtheria, tuberculosis (mainly cornified tuberculosis, invasive tuberculosis, and extra-pulmonary tuberculosis in the dissolution phase of dissemination).
- Lymphocytic type: Commonly seen in pertussis, chickenpox, infectious mononucleosis, infectious lymphocytosis, tuberculosis, etc.
- Monocytic type: Commonly seen in tuberculosis, cytomegalovirus infection, subacute bacterial endocarditis, etc.
- Eosinophilic type: Commonly seen in parasitic infections such as schistosomiasis, filariasis, malaria, echinococcosis (encysticercosis), etc.
Malignant tumors
Most often seen in patients with advanced malignancies such as lung and gastrointestinal tract, especially after metastasis to liver and bone marrow. Multiple myeloma, Hodgkin’s disease, melanoma osteosarcoma, breast cancer, and choriocapillaris epithelial carcinoma are also common underlying conditions.
Poisoning
- Chemical factors: such as mercury, organophosphorus, benzene, nitrite, and other poisoning.
- Pharmacological: such as arsenic agents, antipyretic and analgesic drugs, sulfonamides, adrenaline glucocorticoids, lithium salts, etc.
- Other: eclampsia, carbon monoxide poisoning, tetrachloroethane poisoning, uremia, ketoacidosis, food poisoning, etc.
Other causes
Acute tissue injury, acute blood loss with hemolysis, and other allergic diseases (e.g., exfoliative dermatitis allergic pneumonia), hyperthermia poisoning, ionizing radiation disease post splenectomy, late pregnancy, etc.
The laboratory findings of the “leukemia-like” reaction are generally only leukocytosis, with erythrocyte, hemoglobin, and platelet counts generally in the normal range, and some intermediate and late naïve erythrocytes/leukocytes in the peripheral blood, but abnormal laboratory findings of the primary underlying disease can be detected, while 70%-80% of patients with leukemia have peripheral abnormalities. Leukemia patients may have primitive or early naïve hematopoietic cells in the periphery.
Bone marrow examination is the gold standard for differentiating “leukemia-like” reactions” from leukemia, with the former having essentially normal ratios of red and megakaryocytes to early myeloid cells <5%, and leukemia having protoinfantile cells in the bone marrow >20%, with severe suppression of the red and megakaryocyte lineages. The results of the study were very positive.
Because the “leukemia-like” reaction is secondary to other diseases, there is no specific clinical manifestation of the disease. The main manifestations are different signs and symptoms of the primary disease. The treatment and prognosis depend on the underlying disease that caused the reaction, and if the underlying disease is curable, the “leukoid” reaction will mostly go away as treatment progresses.