Myelofibrosis-osteosclerosis syndrome associated with erythroid hypoplasia in a dog

Idiopathic pure red cell aplasia and nonregenerative immune-mediated anemia in dogs: 43 cases (1988-1999)

OBJECTIVE

To examine clinical features, laboratory test results, treatment, and outcome of dogs with pure red cell aplasia (PRCA) and idiopathic nonregenerative immune-mediated anemia (NRIMA).

DESIGN

Retrospective study.

ANIMALS

43 dogs with severe nonregenerative anemia.

PROCEDURE

Medical records of dogs determined to have PRCA, NRIMA, or ineffective erythropoiesis on the basis of bone marrow analysis between 1988 and 1999 were reviewed. Criteria for inclusion were > or = 5-day history of severe nonregenerative anemia (Hct < 20%; < 60.0 x 10(3) reticulocytes/microliter) with no underlying diseases. Information was retrieved on signalment, clinical signs, laboratory test results, treatment, and outcome.

RESULTS

Median age of the dogs was 6.5 years. Spayed females and Labrador Retrievers were significantly overrepresented. Median Hct was 11% with no evidence of regeneration (median, 1.5 x 10(3) reticulocytes/microliter). Direct Coombs' test results were positive in 57% of dogs. Biochemical abnormalities included hyperferremia and high percentage saturation of transferrin. Bone marrow findings ranged from PRCA (5%) to erythroid hyperplasia (55%). Myelofibrosis was common. Dogs were treated with immunosuppressive drugs and the response was complete, partial, and poor in 55, 18, and 27% of the dogs, respectively. Mortality rate was 28%.

CONCLUSIONS AND CLINICAL RELEVANCE

An immune-mediated pathogenesis should be considered in dogs with severe, nonregenerative anemia, normal WBC and platelet counts, hyperferremia, mild clinical signs, and no evidence of underlying disease. Bone marrow findings range from the rare PRCA to erythroid hyperplasia. Myelofibrosis is often detected in affected dogs and may prevent bone marrow aspiration.

Clinicopathological features of seven cases of canine myelofibrosis and the possible relationship between the histological findings and prognosis

Seven dogs with non-regenerative anaemia were diagnosed as having myelofibrosis on the basis of the presence of collagen and increased deposits of reticulin fibre in the haemopoietic spaces of bone marrow core biopsies. A scoring system was used to assess the cellularity of the marrow and the amounts of collagen, reticulin and haemosiderin present. These scores, together with the haematological findings, were compared with the dogs' responses to treatment and their outcome. Treatment consisted of blood transfusions, where required, and anabolic steroids and corticosteroids. Three dogs deteriorated and were euthanased within three months of diagnosis, but the other four recovered fully. There was no correlation between the collagen and reticulin scores, or the degree of anaemia and the outcome, but the four dogs which recovered all had a macrocytosis when first examined. There was no evidence of an underlying lymphoproliferative or myeloproliferative disease in any of the seven cases.

A review of myelofibrosis in dogs

Myelofibrosis is a proliferative response of the bone marrow fibroblasts. Myelofibrosis can be classified as primary or secondary depending on the underlying etiology. Primary myelofibrosis is a myeloproliferative disorder in humans in which there is a clonal proliferation of a pluripotent stem cell. Hemopathology includes finding nucleated red blood cells and immature granulocytes in the circulation, extramedullary hematopoiesis, and myelofibrosis. The proliferation of the bone marrow fibroblasts is not clonal in origin. To the best of this author's knowledge, this type of myelofibrosis has not been reported to occur naturally in the dog. Secondary myelofibrosis has been reported in the dog associated with neoplastic conditions, irradiation, congenital hemolytic anemias, and a variety of unknown etiologies. It has been shown in some cases of myelofibrosis that there is often concurrent bone marrow necrosis. Bone marrow necrosis has been documented in dogs with Ehrlichiosis and septicemia, and associated with drug treatment, including estrogens and cephalosporins. It is though that this necrosis is due to the destruction of the bone marrow microvasculature and/or hematopoietic elements. Release of growth factors by inflammatory cells may lead to the subsequent fibroblast proliferation. Several cases of secondary myelofibrosis in female laboratory beagles have been recently observed. These dogs present with a severe nonregenerative anemia and often a mild neutropenia with varying degrees of myelofibrosis in the bone marrow. Some animals have had concurrent bone marrow necrosis. At this time, the exact etiology is unknown.