Abstract
An approximately 12 year-old, 37.4 kg, adult male northern sea otter (Enhydra lutris kenyoni) maintained in a semi-closed, 68,500 litre outdoor habitat presented with lethargy, mild weight loss and hind-end weakness. Physical exam findings included moderate loss of muscle mass, evidence of poor grooming and marked peripheral lymphadenopathy. Radiographs and ultrasound showed hepatomegaly and an enlarged mediastinal lymph node. Cytology of needle aspirates and histopathology on biopsies of inguinal lymph nodes confirmed lymphoma. Haematology showed neutropenia and poorly differentiated lymphocytes as the predominant cell type indicative of advanced stage (Stage V) lymphoma.
Chemotherapy was elected in order to attempt to improve quality of life. The initial modified L-COAP protocol was based on established dog and ferret protocols and included L-asparaginase (10,000 iu/m2 SC), cyclophosphamide (250 mg/kg PO), vincristine (0.5 mg/m2 IV), cytosine arabinoside (300 mg/m2 SC), and prednisone (starting dosage of 1 mg/kg PO BID) . Surface area was calculated to be 1.1 m2 using the formula SA= k x (BW2/3) x 10-4 where k = 9.9 based on the ferret. Weekly intravenous vincristine was administered for 6 weeks. Maropitant (1 mg/kg SC) was given during chemotherapy if vincristine was administered and for two days orally after the procedure. All physical examinations and chemotherapy involving intravenous administration via the jugular vein was conducted under general anesthesia with midazolam (0.07 mg/kg) and fentanyl (0.22 mg/kg) given intramuscularly and maintained with isoflurane. Naltrexone (0.44 mg/kg IM) was given at the end of each procedure. Initial response was excellent and lymph nodes regressed dramatically, peripheral blood normalized and the otter's attitude and strength improved. Disease progression was noted at week 6 and lymphadenopathy, peripheral blood changes, and weakness recurred. A new protocol including prednisone (starting dosage 20 mg PO BID) and doxorubicin (30 mg/m2 IV given every three weeks) was initiated in an attempt to rescue the remission. Diphenhydramine (0.6 mg/kg PO) was administered on the morning of each doxorubicin treatment, an electrocardiogram tracing was taken during the injection of doxorubicin, and maropitant was given as in the first protocol. Early response was excellent. However, after 3 treatments of doxorubicin and coincident again with reducing prednisone dosage, lymph nodes began to enlarge and the otter became weaker. A rescue protocol including prednisone (0.5 mg/kg PO BID), lomustine (70 mg/m2 PO q21 days), and L-asparaginase (400 iu/kg SC q21 days) was initiated. Denamarin (SAMe) was given at 18 mg/kg PO with lomustine as a hepatoprotectant for possible lomustine liver toxicity.
In addition, a novel autologous vaccine therapy was attempted. Inguinal lymph node wedge biopsies were harvested and shipped in culture media to Colorado State University. Protein was collected from the membrane fraction of the cells and formulated in cationic liposomal DNA complexes as an adjuvant. The otter was given 2 ml of vaccine containing 100 µg of autologous membrane protein subcutaneously weekly. The otter received two dosages.
The otter tolerated all treatments very well and was, for the most part, described to be in very good body condition and with normal appetite, behaviour and activity by husbandry staff for the duration of the course of his disease. However, 148 days after the initial diagnosis of lymphoma, the otter was found to be slow to accept his morning food. His inappetence continued through the day. The next day he was found very weak and lethargic and he was anesthetized for placement of an intravenous catheter and stabilization. A complete blood count and serum chemistry indicated liver failure and marked leukopenia characterized by a severe neutropenia. The otter continued to deteriorate through the day and, due to the poor prognosis, was euthanized with pentobarbital.
The most significant gross findings at necropsy were marked generalized lymphoadenopathy, hepatosplenomegaly and scattered hemorrhagic ulcers throughout the greater curvature of the stomach. The pericardium was thickened and contained approximately 5 ml of turbid, bright yellow exudate and there was pronounced bilateral pulmonary congestion and edema. Histopathology revealed massive expansion and effacement of lymph nodes by dense sheets of intermediate sized round cells with variably distinct cell members, scant eosinophilic to clear cytoplasm and high nuclear to cytoplasm ratio. The nuclei are central and round to oval and occasionally convoluted with finely reticulated to vesiculated chromatin. The mitotic index is low, there is a small amount of dispersed karyorrhectic and pyknotic debris and moderate accumulation of hemosiderin laden macrophages. The microscopic features were suggestive of lymphoblastic lymphoma. A few to moderate growth Staphylococcus aureus were recovered from the lung, lymph node, urinary bladder, bronchus and spleen and attributed to secondary or opportunistic invasion and polymerase chain reaction of pooled tissues proved negative for canine distemper virus, mollicutes, universal herpesvirus, apicomplexa and phocid distemper virus.
This case report highlights the successful management of lymphoma in a sea otter with return of a high quality of life and tolerance for a variety of chemotherapeutic agents. This is the first antemortem diagnosis of lymphoma in a sea otter and, to the authors' knowledge, the first report of the use of chemotherapy in an otter as well as the first use of novel autologous vaccine therapy in a sea otter.
Acknowledgements
A great many people lent their expertise to our efforts to ensure that Milo had the highest level of care possible. The authors would like to thank Brian Sheehan, Roberta Cavanaugh, Katie Becker, Julie Gorman, Phil Wong, Indrajit Canagaratnam, Sandra Smith, Kristen Plancarte, Neil Fisher and the absolutely incredible marine mammal husbandry team as well as our amazing veterinary technicians - Chelsea DeColle and Gwyneth Nordstrom - at the Vancouver Aquarium. A great number of experts around the globe who helped in various ways includes (but is not limited to): Joerg Mayer, Kathi Ellis, Mike Murray, Dr. G. Ogilvie, Dr. Charney, Marina Ivancic, Allison Peterson, Daniel Lewer, Tanya Wright, Caroline Marschner, Todd Schmitt, and Miriam Kleiter.