Clinical-pathological findings and cytochemical characterization of myelomonocytic leukaemia in 5 dogs

Abstract

The initial clinical signs of 5 dogs diagnosed to have myelomonocytic leukaemia lacked specificity and one dog was asymptomatic. Clinical findings were variable but splenomegaly or spleno-hepatomegaly was detected. All dogs had either macrocytic or normocytic normochromic, non-responsive anaemia and thrombocytopenia. The total leukocyte count ranged from 10 400 to 422 400 per μl of blood with 4 dogs having increased numbers. Cellular morphology in Wright-stained blood and marrow films revealed the presence of predominantly myeloblasts with or without monoblastoid and monocytoid cells and indicated a diagnosis of myeloblastic leukaemia in 2 cases and of myelomonocytic (blast type) in 3 cases. However, cytochemical characterization of cells in blood and marrow smears for granulocytic (alkaline phosphatase) and monocytic (lipase and non-specific esterase) markers led to all being classified as myelomonocytic (blast type) leukaemia. The number of cells reacting positively for these markers was invariably increased in blood, in marrow, or in both. In this regard, staining for peroxidase, chloroacetate esterase, phospholipid, and glycogen was found to have no or limited differential value. The clinical outcome was poor. Because of the advanced stage of the disease, 2 dogs were not treated and 2 of the 3 dogs given anti-cancer treatment survived for less than 2 weeks. One dog responded objectively to cytoreductive therapy and survived 8 months. Myelomonocytic transformation of an essentially monoblastic leukaemia is thought to have occurred in this case over a period of 3 months while on maintenance therapy with fatal outcome 5 months later.