Multiple cytopenias associated with monocytic proliferation in a dog.

An unusual combination of blood cytopenias and monocytic proliferation was observed in a dog. Initial hematologic findings included severe thrombocytopenia, neutropenia, mild nonregenerative anemia and apparently normal bone marrow. Subsequently, a severe persistent monocytosis developed and the bone marrow became populated with monocytes and cytophagic macrophages. Splenomegaly was due to reticuloendothelial hyperplasia and extramedultary hematopoiesis. Treatment consisted of splenectomy and azathioprine but the response was poor and the dog was euthanized. Postmortem examination revealed a hypocellular bone marrow which contained moderate numbers of monocytes and plasma cells. Neoplastic proliferation was absent in visceral organs. No definite diagnosis was established; chronic blood cell consumption, perhaps immune-mediated, may have been responsible for the extensive reticuloendothelial hyperplasia and cytophagia.