Monocytic leukemia in a horse.

The research article describes a case study of monocytic leukemia, a form of blood cancer, found in a six-year-old Hassian gray gelding. The horse displayed impaired performance, coughing, colic, and swelling in different parts of the body, among other symptoms, which led to the diagnosis.

Clinical Examination

• The horse had a history of impaired performance, slight cough, colic (abdominal pain), and edema (swelling due to fluid accumulation) in the ventral abdomen, prepuce, and legs. It also had reduced skin turgor (elasticity), pale mucous membranes, forced costoabdominal breathing, reduced venous return, and enlarged lymph nodes.
• The horse’s spleen, known as splenomegaly, was abnormally large. These signs pointed towards a possible illness, which was confirmed with the hematologic (blood) findings.

Hematologic Findings

• The blood test results showed anemia (low red blood cell or hemoglobin count), leukocytosis (high white blood cell count), and a high percentage of monocytoid leukemic cells, indicating a form of leukemia.

Necropsy Findings

• Post-mortem examination revealed generalized lymphadenopathy (disease of the lymph nodes), splenomegaly (enlarged spleen), ascites (accumulation of fluid in the abdomen), hydrothorax (fluid in the pleural cavity), and a thickened gut wall.
• There was a massive infiltration of the monocytoid leukemic cells into multiple organs including lymph nodes, spleen, bone marrow, liver, gut wall, kidneys, and choroid plexus (part of the brain).

Cell Analysis

• The leukemic cells demonstrated the capability to engage in phagocytosis (the process by which cells engulf and destroy other cells or particles) when mixed with latex particles, as seen under light and electron microscopy.
• The leukemic cells also displayed significant enzyme activity with alpha-naphthyl-acetate and naphthol-AS-acetate esterase, but a weak reaction with naphthol-AS-D-chloroacetate esterase.
• An alkaline phosphatase activity test showed minimal activity in a few leukemic cells. This limited activity suggests the disease’s physical impact on the cells.

Scanning Electron Microscopy

• Under microscope, the surface of the leukemic cells showed distinct irregularities such as ruffles and ridge-like profiles. Such deformities on cell surfaces are frequent in diseased or cancerous cells.

Conclusions

• The combination of clinical signs, hematologic findings, necropsy results, and the physical characteristics of the leukemic cells led to the diagnosis of monocytic leukemia. Such a conclusion ruled out other potential forms such as lymphocytic and granulocytic leukemia.