Myelodysplastic Syndromes

Abstract

Myelodysplastic syndromes (MDS) are a group of acquired clonal hematologic disorders, described in dogs, cats, horses, and humans, that originate from acquired genetic mutations in hematopoietic stem cells. Major subtypes of MDS must be differentiated to better define appropriate treatment and establish a prognosis. Myelodysplastic syndromes must also be differentiated from secondary dysmyelopoiesis due to diseases, drug and toxin exposure, robust hyperplasia, or congenital disorders. The World Health Organization modified the French–American–British classification system incorporating diagnostic information such as cytogenetics, immunologic markers, and molecular genetics. Treatment of dogs with MDS with refractory cytopenia has included prednisolone, cyclophosphamide, cytosine arabinoside, and erythropoietin. Secondary dysmyelopoiesis includes nonclonal dysplastic conditions that should not be classified as MDS. As in dogs, MDS can be difficult to differentiate from secondary dysmyelopoiesis using morphology alone, particularly in presumed immune-mediated anemia. Myelodysplastic syndrome, most consistent with MDS-excess blasts, has been described in a Quarter Horse.