• Companion Animals
• Veterinary Medicine
• Oncology & Hematology
• Working Animals & Livestock

• Companion Animals
• Oncology & Hematology
• Working Animals & Livestock

Amy N. Schnelle, DVM, University of Illinois, Urbana, Illinois, USA, gave an overview of leukemia and myeloproliferative diseases in veterinary medicine. The clinical signs of leukemia can be vague and include lethargy, change in behavior, weight loss, petechiation, cytopenias, and enlarged peripheral lymph nodes or spleen. Often, these cases are detected incidentally, particularly with chronic lymphocytic leukemias (CLLs). The survival times for acute leukemias (days to months) are generally worse than for the chronic leukemias (months to years). Biochemistry results can be highly variable. Sometimes, they are normal; however, abnormalities may include hyperglobulinemia, unexplained hypercalcemia, or others related to specific organs that are affected.

Although the human criteria and nomenclature were revised by the World Health Organization in 2008, the veterinary classifications have remained unchanged. Acute myeloid leukemia includes myeloblastic, monocytic, and myelomonocytic subtypes. Treatment response is comparable among subtypes, with a survival time ranging from 1 to 4 months. Chronic myeloid leukemia is rare, consisting of many well-differentiated cells. One of the difficulties in diagnosing acute lymphoid leukemia (ALL) is distinguishing Stage V lymphoma that has spread to bone from a true lymphocytic leukemia that has originated in the bone. The survival time for ALL ranges from 2 to 4 months. In animals with CLL, a lymphocyte count > 20,000/μL becomes a cause for concern.

Acute erythroid leukemias are not as common as in the past. This disease consists of increased blasts with a predominance of erythroid cells, and in cats it is associated with feline leukemia virus (FeLV) infection. Chronic erythroid leukemia, also referred to as polycythemia vera, is characterized by a very high hematocrit. In these cases, it is important to rule out other possible causes of erythrocytosis. Cases of megakaryocytic leukemias are very rare and usually have a poor prognosis. Chronic megakaryocytic leukemia is also extremely rare and is characterized by essential thrombocytopenia and a platelet count > 1 million/μL.

Atypical cell morphologies are the hallmark of myelodysplasia. Cell characteristics include binucleation, laststage mitotic figures, megaloblastic cells, and hyper- or hyposegmented nuclei. This disorder is also associated with feline retroviruses such as FeLV and may develop into leukemia. Multiple myeloma is a proliferation of plasma cells. Monoclonal gammopathy, lytic bone lesions, light-chain (Bence-Jones) proteinuria, and > 20% plasma cells in bone marrow are the criteria for a multiple myeloma diagnosis.

Several testing methodologies are used to diagnose and characterize leukemias. A complete blood count provides a white blood cell count and helps determine the presence of concurrent cytopenias or an inflammatory leukogram. Blood smear review identifies blast cells or dysplastic morphology. A bone marrow evaluation provides more cytologic detail and makes it easier to evaluate blast percentages. Cytochemical staining is an older method that has largely been replaced by immune-based methods, but it remains useful in some cases. Different lymphomas, such as B cell lymphoma and T cell lymphoma, can be differentiated with immune-based methods. Flow cytometry and polymerase chain reaction are also used to further delineate lymphoproliferative disease.

As leukemia research in humans continues to make advances in research, veterinary medicine is further behind in the field. But, concluded Dr. Schnelle, the hopes in the future are to find correlations with effective therapies and testing for minimal residual disease as well as further research into mutations with prognostic value.

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