Subleukaemic T-Lymphoblastic Leukaemia in a Horse.

The study reports a unique case of a 20-year-old horse that was diagnosed with a rare type of leukemia, specifically subleukaemic T-lymphoblastic leukaemia. The horse presented symptoms including loss of appetite and weight, occasional fever, cough, fluid accumulation beneath the skin, and reduced endurance. Despite thorough evaluation, the cause of these symptoms was only found after its death.

Background

• The horse, a Dutch Warmblood gelding, displayed several clinical signs such as anorexia, weight loss, periodic fever, cough, fluid buildup under the skin, and diminished stamina during activity.
• A haematological evaluation was conducted on the horse which showed the presence of immature blood cells (blast cells), lowered levels of lymphocytes (a type of white blood cell), mild thrombocytopenia (low platelet count), and anaemia (low red blood cells).
• However, there was no leucocytosis which is an increase in the number of white cells in the blood, usually during infection.

Diagnosis and Results

• Further tests showed elevated levels of aspartate aminotransferase and gamma-glutamyl transferase activities (indicative of liver damage), and increased triglyceride concentrations (type of fat in blood).
• Unfortunately, 22 days after the initial visit, the horse passed away, exhibiting clinical signs like decreased appetite, increased body temperature, rapid breathing (tachypnoea), and fast heartbeat (tachycardia).
• A post-mortem examination revealed minor spenomegaly (enlarged spleen) but there was no notable enlargement of lymph nodes, or observable masses or nodules in any organs.

Post-Mortem Examination Findings

• However, microscopic examination of the tissues showed cancerous cells in certain areas of the lymph nodes including the mediastinal (chest region), axillary (armpit), mesenteric (abdominal), and renal (kidney).
• The bone marrow was densely packed with a large number of abnormally large round cancerous cells. These cells had round nuclei with clear nucleoli and very little cytoplasm.
• The cancerous cells tested positive for CD3 (an indicator of T cells – a type of white blood cell), but tested negative for CD20 (an indicator of B cells – another type of white blood cell), BLA36, CD204, Iba-1, CD204, and granzyme B.

Interpretation and Conclusion

• Based on these findings, the horse was diagnosed with a rare type of cancer known as subleukaemic T-lymphoblastic leukaemia.
• This particular type of leukaemia is rare and, to the best of the researchers’ knowledge, this is the first report of this cancer in horses.