Myelodysplasia: Differentiating Neoplastic from Nonneoplastic Syndromes of Ineffective Hematopoiesis in Dogs

Abstract

In the context of human hematopathology, the terms myelodysplasia and Myelodysplastic Syndromes (MDS) are applied to disorders of hematopoiesis that are clonal, neoplastic, and, in most forms, manifested as ineffective hematopoiesis with characteristic morphologic abnormalities in multiple cell lines. Studies of human patients have provided the conceptual framework that MDS evolve from a multipotential hematopoietic stem cell (CFU-GEMM) that has undergone neoplastic transformation as the result of acquired genetic mutations. The diagnosis of MDS in human patients is based largely on morphologic examination of marrow but can be confirmed by detection of cytogenetic abnormalities. Spontaneous, neoplastic myelodysplasia occurs in dogs, but rarely. Nonneoplastic syndromes of ineffective hematopoiesis are more common in dogs, can resemble MDS, and are probably immune mediated in many cases. Drugs and their metabolites are potential causes of dysmorphic maturation and ineffective hematopoiesis. Without methods to confirm clonality by cytogenetic analysis, the diagnosis of neoplastic myelodysplasia in dogs is based on light microscopic examination of bone marrow smears. This paper discusses and illustrates the characteristic morphologic and cytochemical features of neoplastic myelodysplasia and nonneoplastic ineffective hematopoiesis in dogs.