Acute myeloid leukaemia (M6B: pure acute erythroid leukaemia) in a Thoroughbred foal

Abstract

A 10-week-old Thoroughbred filly was referred for anaemia of 4 weeks' duration. Haematology revealed severe anaemia and panleucopenia. Cytological examination of bone marrow smears revealed a myeloid to erythroid ratio <0.02:1 (reference range 0.5-2.4:1.0) and an abundance of erythroid precursor cells. The erythroid cell population included rubriblasts, prorubricytes and rubricytes, with only scant numbers of metarubricytes present. There were numerous mitotic erythroid cells, some of which were atypical and megaloblastic. These cytomorphological changes are consistent with pure acute erythroid leukaemia. No treatment was instituted and the filly died three days after presentation. This case illustrates the need to consider both haematology and bone marrow findings to establish a diagnosis of pure erythroid leukaemia. To our knowledge, there is no documented case of acute myeloproliferative disease in horses involving cells of erythroid lineage, but this condition should be considered a differential diagnosis for horses presenting with anaemia.

Equine acute erythroid leukemia

“…Clinical signs, hematological and cytological findings in this case are consistent with equine AML M6B (FORBES et al, 2011) and constitute evidence that allow the diagnosis of neoplasia (VALLI et al, 2002;McMANUS, 2005;FIGHERA & GRAÇA, 2010). In addition, anatomopathological aspects (histological and macroscopic) observed in the equine species are similar to those reported cases of this form of leukemia in other species (TOCHETTO et al, 2011).…”

“…Horses with myeloproliferative disorders in general do not show breed or age predisposition and, apparently, males seem to be more often affected (TAINTOR, 2012). In this case, age and sex were similar to the only described case of AML M6B in this species (FORBES et al, 2011). Similar to what is described in the literature for equines, cats, humans and mice affected by AML M6B (VALLI et al, 2002;FORBES et al, 2011;TOCHETTO et al, 2011), this young horse developed a three-month history of anemia and progressive weight loss as clinical signs.…”

“…Therefore, only the phenotype (cytologic and histologic aspects) was considered to establish a final diagnosis in this case. The absence of pathological data of AML M6B in horses is due to the fact that a necropsy was not conducted in one reported case (FORBES et al, 2011).…”

“…The forms of myeloproliferative diseases previously described in horses include myeloblastic leukemia, chronic lymphocytic leukemia, chronic granulocytic leukemia, acute myelomonocytic leukemia, acute monocytic leukemia and eosinophilic leukemia (TAINTOR, 2012) and, more recently, acute erythroid leukemia (FORBES et al, 2011). The latter represents an extremely rare form of leukemia in horses, being reported more often in mice and cats, occasionally in dogs and rarely in cattle (FIGHERA & GRAÇA, 2010;TOCHETTO et al, 2011).…”

Presumptive pure erythroid leukemia in a dog

“…4,11 Comparatively, AML-M6b is far more frequently seen in cats, usually in association with Feline leukemia virus infection, while the first equine case of AML-M6b was described in a Thoroughbred filly in 2011. 9 In human beings, M6a erythroleukemia is more frequently observed. 16 In contrast to a previous study, 18 but similar to human beings with AML-M6b, the dog in the current study had combined blood cytopenias, likely due to myelophthisis.…”