A 13-year-old, intact male ring-tailed lemur (Lemur catta) with a 10-day history of depression, anorexia, polyuria, and polydipsia was referred to the Veterinary Medical Teaching Hospital, University of Florida for evaluation. The lemur was in poor body condition, but no other abnormalities were noted on the physical examination. A complete blood count and serum biochemistries revealed that the animal was anemic, hypoproteinemic (with hypoalbuminemia and normoglobulinemia), and hyponatremic. Whole body survey radiographs were unremarkable. An abdominal ultrasound revealed a homogenous increase in echogenicity of the liver, while the spleen appeared enlarged with mottled parenchyma. Ultrasound-guided aspirates were taken of the liver and spleen, and a bone marrow aspirate was also collected. Cytology of the bone marrow aspirate revealed that the myeloid and erythroid series was complete with orderly maturation. The myeloid:erythroid ratio was increased at 4:1. Small numbers of large, immature mononuclear cells suggestive of monocytes were seen. These cells had a variable nuclear:cytoplasmic ratio and large, prominent, irregular nucleoli. Erythrophagocytosis was also observed. The sample was interpreted as a possible malignant histiocytic infiltrate with relative myeloid hyperplasia and marked erythroid hypoplasia. Both the liver and spleen contained populations of large anaplastic mononuclear cells, similar to those seen in the bone marrow. Malignant histiocytosis was suggested as a possible diagnosis. Biopsies of the bone marrow and liver, on histopathologic examination, revealed infiltrates of anaplastic, round, neoplastic cells.
The lemur was euthanatized because the owner did not wish to pursue treatment. On necropsy, neoplastic cells were found in the spleen, liver, lung, kidney, multiple lymph nodes, small intestines, pancreas, and bone marrow. Further studies, including immunohistochemistry and electron microscopy, are being undertaken to further identify the neoplastic cell population.