[Case report: polycythemia in a horse].

The research paper presents a case study of a 13 year old Thoroughbred horse that struggled with polycythemia, a condition characterized by an elevated level of red blood cells. This was detected via a high packed cell volume (72%) despite ongoing therapy. Notably, the horse’s liver enzymes were excessively high and showed fibrosis. Despite treatments, the horse was euthanized due to the severe prognosis resulting from liver biopsy findings; post mortem examination also revealed a granular cell myoblastoma in the lungs and other health issues. The main diagnosis remained as polycythemia vera.

Case Overview

• The study revolves around a Thoroughbred horse initially presented for a single mild-exercise-induced collapse. The clinical examination discovered an unusually high packed cell volume (PCV) of 72%, a hemoglobin level of 24.9 g/l, and 15.2 million erythrocytes/microliters; all indicting a high concentration of red blood cells, characteristic of a condition called polycythemia.

Finding and Diagnostics

• Various tests were conducted to confirm and identify potential causes of this condition. Erythropoietin concentrations were normal, suggesting that overproduction of this hormone was not leading to increased red cell production. Tests for neoplasms, specifically carcino-embryonic antigen, were also negative, ruling out cancer as a potential factor.
• Despite continuous intravenous therapy to lower red cell count, the PCV never fell to a normal levels, persisting the abnormal red cell count. Interestingly, the horse behaved normally displaying neither discomfort nor signs of syncope (fainting), confirming that the condition was chronic and likely asymptomatic to this point.
• The liver enzymes of the horse were significantly elevated, a liver biopsy showed severe fibrosis suggesting a chronic disease process was happening in the liver.
• An examination of the sternal bone marrow aspirate did not show any abnormalities, meaning there was likely no problem with marrow production of red blood cells.

Treatment and Outcome

• The horse continued to be treated with repeated phlebotomy for 7 days in an attempt to reduce red cell concentration but the PCV never fell below 50% indicating a persistent relative increase in red cell count. Despite the escalated values, the horse showed no signs of discomfort.
• Due to the poor prognosis of the liver disease discovered in the biopsy, the horse was ultimately euthanized 11 days post hospitalization.
• An autopsy revealed a granular myoblastoma in the lungs, severe fibrosis of the liver, mild acute tubular nephrosis in the kidneys, activation of the erythropoietic cells in the bone marrow and thrombosis of the abdominal aorta.
• The diagnosis of primary absolute polycythemia (polycythemia vera) was confirmed post mortem, although the potential for a secondary polycythemia spurred by the lung tumor was not entirely excluded but considered unlikely due to the absence of other typical signs of this condition.

Conclusion

• The report provides valuable insights about polycythemia in horses and emphasizes the importance of comprehensive diagnostics, including testing for neoplasms and liver function, to identify potential underlying causes and inform the best course of treatment.