Abstract
A 12-year-old female red panda (Ailurus fulgens) from the Riverside Zoo, Nebraska presented to the Zoological Medicine Service, Colorado State University, in October 1997 with a 1-year history of partial anorexia and a recent abdominal enlargement. Physical examination under anesthesia was unremarkable. However, a complete blood cell count revealed a marked leukocytosis with predominantly toxic-appearing mature neutrophils, and a moderate left shift (total white blood cell count=164.0x103/µl, with 124.6x103/µl segmented neutrophils, and 14.8x103/µl band neutrophils). A mild anemia (PCV=29%) was also detected.13
The animal’s condition remained unchanged despite a 2-week course of 2.5 mg/kg enrofloxacin (Baytril, Bayer Animal Health, Shawnee Mission, KS, USA), and 15 mg/kg amoxicillin (Amoxi-inject, SmithKline Beecham, Exton, PA, USA) given intramuscularly twice daily. A physical examination under anesthesia was repeated 3 weeks after initial presentation and revealed marked generalized icterus with hepatomegaly and splenomegaly. Abdominal ultrasound confirmed the splenic and hepatic enlargement and revealed a mild ascites. Fine-needle aspirates of the liver were performed for cytology and anaerobic, aerobic and fungal culture. No growth was obtained from the cultures, and the cytology indicated hepatocellular degeneration. Thoracic radiographs were unremarkable except for mild peribronchial opacity. At this time, the hemogram indicated a marked leukocytosis (257.0x103/µl) characterized by a neutrophilia with a shift toward immaturity (i.e., mature neutrophils=67.4% [173.1x103/µl], band neutrophils=4.1% [10.5x103/µl], and metamyelocytes=2% [5.2x103/µl]). There was also another cell type present which comprised 19.4% (49.8x103/µl) of the total white blood cells. These cells were slightly larger than the neutrophils and had light basophilic cytoplasm with fine, uniform deep basophilic granules and a lobated nucleus with a clumped chromatin pattern. Upon comparison with blood from a healthy red panda, it was determined that these cells were basophils. The rest of the white blood cell count consisted of 5.1% small lymphocytes (13.2x103/µl) and 2% monocytes (5.2x103/µl). In addition, there was a marked thrombocytosis (1,276x103/µl) and a mild anemia with a nucleated red blood cell count of 5.2x103/µl. A bone marrow aspirate of the proximal left humerus was performed and revealed marked myeloid and megakaryocytic hyperplasia. There were increased numbers of blasts present with some particles containing up to 17% blasts. Many basophils were also present in the marrow. The chemistry panel revealed evidence of liver disease with hyperbilirubinemia (5.1 mg/dl), mildly increased ALP (118 IU/L), GGT (49 IU/L), ALT (176 IU/L), and AST (310 IU/L) and hypoalbuminemia (1.8 g/dl).10 No growth was obtained from two consecutive blood cultures, and routine fecal examination for endoparasites was negative.
The antibiotics were changed to 100 mg/kg ticarcillin/clavulanic acid (Timentin, SmithKline Beecham, Exton, PA, USA) intramuscularly twice daily, and it was additionally treated with 250 ml lactated Ringer’s solution subcutaneously once daily. Despite the therapy, its condition deteriorated. Abdominal laparoscopy was performed, and the liver was diffusely swollen and tan in color, with a mottled appearance. When biopsied, the liver was extremely friable and did not bleed. Some hemorrhage of unknown source was encountered, and the procedure was terminated; however, it died shortly thereafter.
A full necropsy revealed florid myeloproliferation within the liver, spleen, and lymph nodes and a severe secondary hepatic lipidosis. In addition, the bone marrow was markedly hypercellular and was dominated by immature myeloid cells. The clinical and pathologic findings were consistent with a diagnosis of chronic myelogenous leukemia (CML).20 Unusual findings in this case include the basophilia and thrombocytosis. In humans, both can occur in association with CML and are considered paraneoplastic syndromes.2,17
CML has been well characterized in humans, and 90% are associated with a specific chromosome abnormality.15 CML is rare in domestic animals and can be difficult to differentiate from a leukemoid reaction caused by inflammation, immune-mediated disease, or as a paraneoplastic syndrome.18 In domestic cats, feline leukemia virus infection has been associated with some cases of myeloproliferative disease.12 Myeloproliferative disorders of the granulocytes and/or monocytes are also rare in non-domesticated species but have been reported in a Texas tortoise (Gopherus berlandieri),19 snakes, a marine toad (Bufo marinus), a Byrne’s marsupial mouse (Dasyuroides byrnei), an African hedgehog (Atelerix albiventris),8 rabbits and rodents,4,7,16 and primates1,3,5 including an orangutan (Pongo pygmaeus).6 Megakaryocytic leukemia is particularly rare, with only one case reported in a non-domesticated species.9 Only a few neoplastic conditions have been reported in red pandas.11,14,18 To the authors’ knowledge, this is the first report of CML in a procyonid, although interestingly, one case of chronic lymphocytic leukemia has been reported in a 7-year-old female red panda.14
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