Acute undifferentiated leukaemia in a dog

Acute undifferentiated leukaemia (AUL) is considered a separate entity in the context of acute leukaemias. AUL is extremely rare in both humans and dogs, has a rapid clinical course and does not respond to treatment. It is characterised by the presence of blast cells within the bone marrow and/or peripheral blood at levels ≥ 20% and even up to 100% of all nucleated cells. Blast cells are unable to be differentiated on morphological, cytochemical and phenotypic criteria into myeloid or lymphoid lineages because of their immaturity and/or atypia.

An 8-year-old German Shepherd dog was referred for depression, asthenia, mild anaemia, thrombocytopenia and marked leucocytosis. Abdominal ultrasound showed hepatomegaly, splenomegaly, bilateral nephromegaly and enlargement of mesenteric lymph nodes. Echocardiography revealed biventricular hypertrophy with abnormal tissue density of the myocardium. Blood and bone marrow smears were composed of 95% unclassifiable and/or atypical blast cells and signs of dysplasia of the erythroid and thrombocytic/megakaryocytic lineages were present. Blast cells were negative for all cytochemical stains used and flow cytometry of peripheral blood revealed 85% of total leucocytes consisting of small-to-medium-sized cells, negative for all lymphoid and myeloid markers except CD45 and CD34. After necropsy, cytology and histology revealed that blast cells had diffusely infiltrated all tissues examined. Both erythroid and megakaryocytic extramedullary haemopoiesis was also detected in the spleen, lymph nodes and liver. All immunohistochemical stains used were negative.

On the basis of all the results, a diagnosis of acute leukaemia involving a very primitive haematopoietic precursor was made.