Brain herniation in a dobermann with polycythaemia vera

Abstract A 1.5‐year‐old, entire, female dobermann presented acutely comatose with seizures and tremors and was found to have marked erythrocytosis with a packed cell volume of 92%. The erythropoietin level was low, and the JAK2 gene mutation testing was negative. Despite multiple phlebotomies and a gradual decrease in packed cell volume, the dog deteriorated and developed respiratory arrest. Euthanasia was elected. Postmortem findings revealed a highly cellular bone marrow with approximately 70% haematopoietic cell lineages, aspiration pneumonia, as well as brain haemorrhage, necrosis and foramen magnum herniation, leading to respiratory arrest. The diagnostic findings were most consistent with polycythaemia vera, in which severe blood hyperviscosity likely caused cerebral hypoperfusion and vascular injury, explaining the neurological signs and postmortem changes. The neurological dysfunction likely contributed to aspiration pneumonia. Reported median survival time in dogs with polycythaemia vera is poor, emphasising the need for improved understanding of the disease to guide future management.