Leukoproliferative disorders in horses

Rapid clinical progression of B-cell chronic lymphocytic leukemia in a horse

CASE DESCRIPTION

A 17-year-old Friesian gelding was examined at a referral hospital because of a 1-month history of mild exercise intolerance and marked lymphocytosis.

CLINICAL FINDINGS

Physical examination revealed no peripheral lymphadenopathy or other abnormalities. Results of an abdominal palpation examination per rectum and thoracic and abdominal ultrasonographic examinations were unremarkable. B-cell chronic lymphocytic leukemia (CLL) was diagnosed on the basis of severe lymphocytosis and positive expression of the B-cell marker CD20 by lymphocytes in the bone marrow and peripheral blood.

TREATMENT AND OUTCOME

Treatment with prednisolone (2 mg/kg [0.9 mg/lb], PO, every other day) and chlorambucil (20 mg/m², PO, every 3 weeks for 2 doses, then every 2 weeks) was initially associated with improvement in clinical signs and a decrease in the lymphocyte count. However, 3 weeks after administration of the first dose of chlorambucil, the lymphocyte count began to increase. One week later, the horse developed episodes of recurrent fever and the lymphocyte count continued to increase. Despite continued administration of the prednisolone-chlorambucil protocol, the horse's clinical condition deteriorated rapidly, and it was euthanized 6 weeks after initial examination at the referral hospital because of a poor prognosis. A necropsy was not performed.

CLINICAL RELEVANCE

B-cell CLL has been infrequently described in horses. This report was the first to describe the use of chemotherapy, albeit unsuccessful, for the treatment of B-cell CLL in a horse. This information should be useful for guiding expectations for prognosis and management of other horses affected with the disease.

Pericardial effusion and congestive heart failure in a horse with multicentric lymphoma

A 20-year-old Warmblood mare was evaluated for acute-onset tachycardia and a one-week history of lethargy and ventral oedema. Haematology revealed leucocytosis with neutrophilia. Ultrasonographic examination revealed pericardial effusion and cardiac tamponade consistent with right-sided congestive heart failure. Abdominal ultrasonography demonstrated loss of definition of the right kidney and a structure adjacent to the kidney suggestive of a renal neoplasm. A tentative antemortem diagnosis of multicentric neoplasia, most likely lymphoma, was made. The horse was subjected to euthanasia due to a grave prognosis. Postmortem examination and histological evaluation were consistent with lymphoma, including infiltration of the cardiac muscle with neoplastic cells. Although lymphoma has been reported to affect the heart, congestive heart failure due to cardiac and pericardial neoplastic infiltration has not been previously reported as the presenting complaint. This case report describes the diagnostic approach to pericardial effusion and congestive heart failure in a mare with lymphoma.

Bone marrow and lymph node evaluation

Evaluation of equine bone marrow and lymph node samples can provide the definitive diagnosis in some cases, and may provide useful information in other cases. Some newer techniques, including immunophenotyping of cells and clonality assays, provide the capability to more precisely identify cells, both as to origin and malignancy. Use of these techniques on equine bone marrow and lymph node samples, and compiling of the data, will eventually provide invaluable information about equine neoplasia that will greatly improve the ability to predict tumor behavior and response to therapy.