ACUTE MYELOMONOCYTIC LEUKEMIA IN A CALF

In a 2-month-old cross-bred calf with paraplegia, results of neurologi c evaluation were suggestive of a spinal cord lesion caudal to L3. The calf bled from the blood sampling site for an extended period after v enipuncture. Leukocytosis, anemia, and thrombocytopenia were observed. The leukocytes were predominantly atypical blast cells. Postmortem ex amination revealed petechial hemorrhages throughout the internal organ s. Bone marrow was pale tan, with no red marrow seen. Atypical leukocy tes were diffusely distributed throughout the body, with penetration o f the spinal cord and spinal roots, particularly in the lumbar region. Atypical leukocytes stained positively for alpha-naphthyl acetate est erase and chloracetate esterase, and stained with Sudan black B. Atypi cal leukocytes expressed class-1 and class-2 major histocompatibility antigens, but did not express specific T-, B-, or null-cell surface an tigens. The final diagnosis was myelomonocytic leukemia. Differential diagnosis of leukemia in calves should include myelogenous leukemia, a nd requires use of various techniques to make a definitive diagnosis.