Idiopathic myelofibrosis in a cat and in three dogs

Idiopathic myelofibrosis accompanied by peritoneal extramedullary hematopoiesis presenting as refractory ascites in a dog

A 2.5-year-old spayed female American Pit Bull Terrier dog presented with a primary complaint of chronic refractory ascites. The dog's CBC displayed a moderate to severe macrocytic, hypochromic, nonregenerative anemia, and a moderate leukopenia as result of a moderate neutropenia and monocytopenia. Microscopic examination of the blood smear showed marked anisocytosis, mild polychromasia, mild acanthocytosis and ovalocytosis, moderate schistocytosis and poikilocytosis, and 4 metarubricytes/100 WBC. Abdominal ultrasonography revealed a homogenous, mild to moderately hyperechoic appearing liver as well as marked amounts of speckled anechoic to slightly hypoechoic peritoneal fluid. Cytology of the ascitic fluid demonstrated a sterile transudate, with evidence of a chronic inflammatory reaction as well as erythroid and myeloid precursor cells, and a few megakaryocytes with occasional micromegakaryocytes. Histologic sections of bone marrow, spleen, and liver were examined, using routine H&E stains, as well as a variety of immunohistochemistry and other special stains. Histopathology of the bone marrow and spleen revealed varying degrees of fibrosis, erythroid, and myeloid hyperplasia, as well as multiple small hyperplastic clusters of megakaryocytes. The megakaryocytes displayed many features of atypia such as increased cytoplasmic basophilia and occasional abnormal chromatin clumping with mitoses. Histopathologic examination of the liver disclosed evidence of mild extramedullary hematopoiesis. This case represents the first report of canine idiopathic myelofibrosis associated with peritoneal extramedullary hematopoiesis, resulting in refractory ascites. Although idiopathic myelofibrosis is a relatively rare condition in dogs, this case demonstrates that ascites caused by peritoneal implants of hematopoietic tissue may be the initial manifestation of myelofibrosis.

Cytologic evaluation of primary and secondary myelodysplastic syndromes in the dog

Myelodysplastic syndromes are a heterogeneous group of acquired primary and secondary alterations of hematopoietic stem cells that result in cytopenias in blood and cytologic features of dysplasia in blood and/or bone marrow. To better understand the cytologic features that would permit differentiation of primary and secondary forms of myelodysplasia, we reviewed 267 consecutive bone marrow reports from dogs. These reports indicated that 34 dogs (12.7%) had dysgranulopoiesis, dyserythropoiesis, and/or dysthrombopoiesis in >10% of granulopoietic cells, erythroid cells, and/or megakaryocytes, respectively. Thirteen dogs had primary myelodysplastic syndromes, and 21 had secondary myelodysplastic syndromes. Of the 13 dogs with primary myelodysplasia, 4 were subclassified as myelodysplastic syndrome with refractory anemia (MDS-RA), and 9 were subclassified as myelodysplastic syndrome with excess blasts (MDS-EB). Secondary conditions associated with dysplasia in the bone marrow included malignant lymphoma (n = 5), myelofibrosis (n = 3), immune-mediated thrombocytopenia (n = 4), immune-mediated hemolytic anemia (n = 5), multiple myeloma with melphalan administration (n = 1), pyometra with estrogen administration (n = 1), polycythemia vera (n = 1), and thrombopathia (n = 1). MDS-RA was characterized by <5% myeloblasts in bone marrow, normal granulocyte maturation ratio, increased erythroid maturation ratio, and dysplastic changes in >15% of erythroid cells. MSD-EB was characterized by >/=5% myeloblasts in bone marrow, high granulocyte maturation and erythroid maturation ratios, >/=32% dysplastic granulocytes, and the presence of small atypical immature myeloid cells. Secondary myelodysplastic syndromes were characterized by <5% myeloblasts in bone marrow, variable granulocyte maturation and erythroid maturation ratios, and variable dysplastic features. These results indicate that morphology alone cannot be used to distinguish primary and secondary myelodysplastic syndromes in dogs.

Myelodysplastic syndrome (MDS), acute myeloid leukaemia (AML) and chronic myeloproliferative disorder (CMPD) in cats

Histological, enzyme histochemical and ultrastructural findings in three cases of feline bone marrow neoplasia are described. The following changes were observed: in myelodysplastic syndrome (MDS), a low medullary blast count, strongly atypical (micromegakaryocytic) proliferative megakaryocytopoiesis, hypoplastic erythrocytopoiesis with impairment of differentiation, multifocal extravasation and lymphoid aggregates; in acute myeloid leukaemia (AML), medullary proliferation of undifferentiated cell types; in chronic myeloIproliferative disorder (CMPD), trilinear medullary proliferation with complete cellular maturation, osteomyelosclerosis and extramedullary haemopoiesis. In two cases (MDS, AML), ultrastructural demonstration of C-type virus particles (feline leukaemia virus) suggested a viral aetiology.