Pearls
- Hemopoietic neoplasia is an area of veterinary medicine undergoing rapid development. Classification schemes are changing and being revised, often in keeping with changes in human medicine. More sophisticated diagnostics support this development and facilitate more accurate diagnoses and, therefore, more effective treatment of affected patients.
- Leukemia is a malignant neoplasm of hemopoietic cells, usually beginning in the bone marrow and associated with the release of malignant cells into the peripheral blood. Leukemia is usually a neoplasm of WBCs but RBCs can also be involved.
- Solid tumors of hemopoietic cells can occur without a leukemic phase, particularly in the case of lymphoid tumors.
- Lymphoid tumors are the most common hemopoietic neoplasm in domestic species, but tumors of neutrophils, eosinophils, basophils, monocytes, megakaryocytes, and erythrocytes also occur. Often cytochemistry, immunohistochemistry, PCR, and other molecular tests are required to determine the cell of origin, particularly with less common tumor types or when neoplastic cells are not well-differentiated.
- Bone marrow examination is usually indicated when there is peripheral blood or solid tissue (e.g. lymph node) evidence of hemopoietic neoplasia.
- Occasionally, the bone marrow contains neoplastic cells which are not being released into the peripheral circulation. In these cases, there may still be indicators on the CBC of a marrow disorder (e.g. cytopenia[s]).
- If there are CBC changes that cannot be explained (cytopenia[s], leukogram changes), bone marrow examination should be done as well as careful examination for lymph node enlargement or other organ involvement.
- Generally, there is no known cause of hemopoietic neoplasia in domestic animals, with 2 important exceptions:
- BLV causes LSA (with or without leukemia) in 5-10% of chronically infected cattle. Often persistent lymphocytosis precedes the development of neoplasia. Cattle with suspected BLV-related lymphocytosis, leukemia, or solid tissue LSA can be tested for the presence of antibodies to the virus (agar gel immunodiffusion test or ELISA is commonly used).
- FeLV causes both degenerative and neoplastic diseases of several different hemopoietic cell types in cats. LSA and lymphocytic leukemia in cats are commonly associated with FeLV infection and viral antigen can be detected by ELISA or immunohistochemistry, or viral DNA can be detected by PCR. Unique among the domestic species are tumors of erythroid cells (erythremic myelosis) or a more primitive hemopoietic cell which can differentiate along both erythrocytic and granulocytic lines (erythrogranulocytic or erythroleukemia) in cats, as a result of FeLV infection.
- Typical peripheral blood findings in erythremic myelosis are severe nonregenerative anemia with the presence of large numbers of nucleated erythrocytes of all stages (from rubriblasts to metarubricytes) and erythrocyte macrocytosis.
- Do not misinterpret the presence of large numbers of nRBCs as indicating a regenerative response. Remember: polychromasia and reticulocytosis are the hallmarks of regeneration. These are not seen in this disease.
definition
All tests on the CBC that evaluate leukocytes. Also, that part of the leukon which is evaluated by examination of a peripheral blood sample (typically does not include leukocyte precursors).
Erythrocyte precursor; often used to refer to metarubricytes in peripheral blood.
