Intravascular leukostasis and systemic aspergillosis in a horse with subleukemic acute myelomonocytic leukemia.

This research outlines a rare case of subleukemic acute myelomonocytic leukemia in a horse, detailing the medical examinations, unsuccessful treatment attempts, and autopsy findings, including fungal infection and unsuccessful in vitro cell cultures attempts.

Introduction to the Case

• Leukemia, which is a cancer of the blood or bone marrow cells, is rarely seen in horses. In this study, the researchers detail an instance of a specific type of leukemia, known as subleukemic acute myelomonocytic leukemia, in an 11-year-old gelding.

Cytological Diagnosis and Laboratory Investigations

• Preliminary diagnosis was made based on cytology – the study of cells. Support for this diagnosis was provided by laboratory testing.
• The neoplastic (cancerous) cells in the horse’s blood and bone marrow were studied and were found to have characteristics consistent with a myelomonocytic origin, pointing to myelomonocytic leukemia.
• The neoplastic cells in the horse’s peripheral blood were also tested with specific antibodies. They reacted to antibodies specific to horse granulocytes (a type of white blood cell), but not to antibodies for T- or B-lymphocytes (other types of white blood cells) or macrophages (cells that digest cellular debris and pathogens). This further supported the diagnosis of myelomonocytic leukemia.

Treatment Attempt and Necropsy Results

• Despite efforts to treat the horse, the attempts were unsuccessful. The horse was euthanized, and an autopsy was performed.
• The autopsy revealed intravascular leukostasis – a severely thickened blood condition due to an excess of white blood cells in the vessel – in all tissues that were examined.
• The autopsy also discovered the presence of fungal hyphae (the branching filament of a fungus) in the interstice of the lung and the submucosa (the second layer) of the colon. This indicated a systemic fungal infection.

In Vitro Cultures

• Researchers isolated nucleated cells from the horse’s peripheral blood and cultured them in a lab setting. The cells survived up to two weeks and showed signs of cell division, but this could not be sustained consistently.
• Another attempt was made to culture frozen-thawed cells stored in liquid nitrogen. Unfortunately, despite achieving temporary success, no permanent cell line could be established from these cells.

Conclusion

• In conclusion, this rare case of subleukemic acute myelomonocytic leukemia in a horse was thoroughly investigated using cytological examination, immunolabeling with monoclonal antibodies, tissue autopsies, and in vitro culturing techniques. However, despite efforts, the disease could not be effectively treated, and cell cultures could not be sustained.