Equine acute erythroid leukemia

Abstract

Acute erythroid leukemia (AML M6) is a hematopoietic neoplasm frequently described in cats and mice, rarely in other animal species. This report describes a case of AML M6 in a yearling Thoroughbred filly. Clinically the horse presented marked pale mucous membranes and exercise intolerance. In addition, the owner and referring veterinarian reported a 30-day history of progressive weight loss. The CBC revealed severe anemia and leukopenia by neutropenia. Cytology evaluation obtained from bone marrow fine needle aspirates evidenced inversion of the myeloid: erythroid ratio (0.2), with 48% of the nucleated cells corresponding to rubriblasts. In addition to the gross evidence of anemia, necropsy findings consisted of splenomegaly and lymphadenomegaly. The diagnosis of AML M6B was confirmed histologically due to splenomegaly and lymphadenomegaly, secondary to neoplastic metastasization.