RESUMO
OBJECTIVE: To describe the clinical presentation, progression, and diagnosis of acute myeloid leukemia (AML) with neutrophilic differentiation in an African lion (Panthera leo). ANIMAL: A 12-year-old male African lion kept at a zoological institution in Colombia. CLINICAL PRESENTATION, PROGRESSION, AND PROCEDURES: The lion presented for anorexia, pale mucous membranes, and a hind limb lameness of acute onset. Feline leukemia virus testing was negative, and repeated blood samples revealed severe anemia, intermittent thrombocytopenia, lymphopenia, and neutrophilia. Coinfection with Anaplasma and Mycoplasma spp and chronic kidney disease were diagnosed based on clinicopathological findings. TREATMENT AND OUTCOME: The lion received symptomatic treatment, doxycycline, and methylprednisolone or prednisolone. Euthanasia was elected due to clinical deterioration and unresponsive anemia, despite the resolution of Anaplasma and Mycoplasma spp infections. AML with neutrophilic differentiation was diagnosed based on bone marrow cytology, histopathology, and immunohistochemistry. CLINICAL RELEVANCE: AML is a rare, aggressive hematopoietic disorder in domestic cats, although it has not yet been reported in nondomestic cats. This is the first description of the clinicopathological, histological, and immunohistochemical features of AML with neutrophilic differentiation in an FeLV-negative African lion that lacked circulating blasts.