Myelodysplastic/Myeloproliferative Neoplasm in a Dog: A Case Report

Myelodysplastic syndrome/myeloproliferative neoplasm (MDS/MPN) is a clonal myeloid disorder with overlapping features of MDS and MPN. This study reports a case of an MDS/MPN in a dog, offering insights into its clinical presentation, diagnostic approach, and potential practical limitations. An 18-year-old intact female mixed-breed dog presented with severe anaemia for 1 month. A complete blood count revealed severe non-regenerative anaemia with marked monocytosis, lymphocytosis, and moderate thrombocytopenia. A peripheral blood smear examination confirmed dysplastic changes, including hypersegmented neutrophils and monocytes with segmented nuclei. The manual differential count of 400 WBCs confirmed neutrophilia and marked monocytosis. The polymerase chain reaction result for infectious agents causing anaemia was negative. Flow cytometric immunophenotyping revealed 45% granulocytes in the peripheral blood, which were CD14⁺ (low) and CD34^- and negative for lymphoid markers (CD5^-/CD21^-). Monocytes comprised 30% of the population, which were CD14⁺ (high), CD34^-, CD5^-, and CD21^-. Bone marrow aspiration cytology revealed marked myeloid hyperplasia with dysplastic changes and erythroid and megakaryocytic hypoplasia. Bone marrow blasts were 16%. No clinical improvement was observed following an immunosuppressive trial for a possible immune-mediated aetiology. Although bone marrow histopathology and necropsy were not performed, the dog was tentatively diagnosed with MDS/MPN. Despite chemotherapy with cytarabine arabinoside and doxorubicin, the dog succumbed 6 days later. This illustrates the clinical presentation, cytological, and immunophenotypic characteristics of an uncommon myeloid disorder, MDS/MPN, which is recently included in veterinary medicine classification, underscoring the need for clear diagnostic criteria and further research to better characterize and differentiate myeloid neoplasms in veterinary oncology.