Feline myelonecrosis and myelofibrosis: 22 cases 1996–2006

A 10-year retrospective study of bone marrow reports was conducted to identify cats with myelonecrosis or myelofibrosis. Of 167 reports that were included in the study, seven (4.2%) had myelonecrosis alone, three (1.8%) had myelofibrosis alone, and 12 (7.2%) had myelonecrosis and myelofibrosis. These cases were divided into five disease categories including immune-mediated anemia (n = 6), myelodysplastic syndrome/myeloproliferative disease (n = 5), infectious diseases (n = 4), chronic renal disease (n = 3), and other conditions (n = 4). Only two cats tested positive for feline leukemia virus infection. All but one cat had a nonregenerative anemia, and some cats were neutropenic or thrombocytopenic. In most cats, myelonecrosis was characterized by diffuse individual cell lysis. Myelofibrosis was characterized by the presence of fibroblasts or collagen or reticulin fibers. The results of this study indicate that myelonecrosis and myelofibrosis occur relatively frequently in cats, that they are associated with a variety of disease conditions, and that myelofibrosis may be a sequela of myelonecrosis.