Myelofibrosis in a dog with non-regenerative anaemia

A 7-year-old Cocker Spaniel presented for lethargy caused by a chronic non-regenerative anaemia (Ht - 12%).

Fig 1. On examination of a blood smear, various RBC morphology changes are present but the predominant finding is the large number of elliptocytes (ovalocytes).
Fig 2. The bone marrow aspirate is paucicellular. A bone marrow core biopsy reveals myelofibrosis whereby the haematopoietic tissue is largely replaced by fibrous tissue.
Fig 3. A closer look at the mature fibrous tissue that lines the trabecular and replaces the bone marrow.

Final Diagnosis

Myelofibrosis associated with a marked non-regenerative anaemia


The RBC morphology seen in the blood smear (+++ ovalocytes) is not specific but it does suggest bone marrow disease (e.g. myelofibrosis or myelodysplastic disease/myeloid neoplasia). The myelofibrosis confirmed on histopathological examination of a bone marrow core accounts for the chronic marked non-regenerative anaemia in this case. This condition can be idiopathic but known causes of myelofibrosis include chronic bleeding, neoplasia, chronic inflammation, the use of myelotoxic drugs including cyclophosphamide and oestrogens, and radiation treatment.