Abstract
An approximately 15 year-old, 952 kg, adult male Steller sea lion (Eumetopias jubatus) maintained in a semi-closed, 189,000 liter captive display pool presented with a history of chronic dental disease and otitis was presented for oral examination that revealed a bullous enlargement of the left hard palate. It that had previously been diagnosed as a bone cyst and the sea lion had been treated with various antibiotics if there were indications of oral pain or unusual amounts of mucopurulent discharge from the left ear. Necrotic boney debris began to be visible from the swelling and associated teeth on the left upper dental arcade. Repeated treatments with antibiotics and carprofen (2 mg/kg PO once daily) resolved most clinical signs over the following six months. However, oral ulceration, occasional hemorrhage, and a foul odour associated with the enlarged palate were noted and increased in severity.
The sea lion was anesthetized with oral diazepam (0.15 mg/kg) followed by medetomidine (0.01 mg/kg) and midazolam (0.1 mg/kg) given by intramuscular injection. The sea lion was then masked and maintained with isoflurane for dental examination. Due to suspected osteomyelitis secondary to tooth root abscess, aggressive debridement of the palatine and maxillary bones was performed, in addition to removal of the left precanine (third incisor) and canine teeth. Although the sea lion appeared comfortable, the defect in the affected bones continued to grow slowly over the following 10 months. A second anesthetic procedure was performed and radiographs showed multiple lytic lesions in the mass-associated maxillary and palatine bones but with no obvious osteoproliferative disease. More teeth were removed and biopsies were taken from the edge of expanding boney defect. Histopathological examination of oral tissue revealed an invasive, poorly differentiated carcinoma.
Due to the diagnosis of a likely locally invasive neoplasia, a treatment plan consisting of surgical debridement coupled with chemotherapy was initiated. Under general anesthesia, the affected area was debulked with a carbon dioxide laser. Carboplatin was chosen as the primary chemotherapeutic agent and was administered at 300 mg/m2 based on a body surface area calculated to be approximately 7 m2 via slow intravenous infusion. Piroxicam (0.2 mg/kg PO once daily) was started the day before the procedure and continued for a total of 5 days for analgesia and as a secondary chemotherapeutic agent. Metoclopramide (0.1 mg/kg SC) was administered intraoperatively due to the expected nausea resulting from the chemotherapy. Laser therapy and chemotherapy were repeated at 4-6 week intervals on two other occasions. Metoclopramide was replaced with maropitant (1 mg/kg SC) during the procedure. The sea lion showed no emesis post-operatively and recovery from the chemotherapy was improved based on better appetite and lack of post-operative emesis. The lesion appeared to have healthier margins and the progress of the neoplasia appeared to have slowed.
Frank oral hemorrhaging, some bouts lasting greater than 30 hours, noted approximately 6 weeks after the last procedure. The sea lion was anesthetized for emergency hemostasis. An exposed left palatine artery was ligated and necrotic tissue debrided. Anesthetic recovery was much slower than during previous procedures and the sea lion died in the early morning. Post mortem examination revealed disseminated neoplasia affecting liver, lung, spleen, thyroid, kidney and heart in addition to the oral cavity. Histopathological examination including the use of cell markers revealed a sarcomatoid carcinoma of the oral cavity with a disseminated undifferentiated sarcomatoid component in multiple viscera. Despite the negative outcome, this case highlights the possibility of providing a high level of palliative care of complicated medical cases in large marine mammal species.
Acknowledgements
The authors would like to thank Brian Sheehan, Billy Lasby and the absolutely incredible marine mammal husbandry team as well as our amazing veterinary technicians - Danielle McLaughlin and Chelsea DeColle - at the Vancouver Aquarium. Dr. Susan Ford at Canada West Veterinary Specialists and Critical Care Hospital, and Dr. Mark Papich, Dr. Laurel Williams, and Dr. Don Thrall at North Carolina State University provided invaluable insight into chemotherapeutics. Dr. John X. O'Connell at Surrey Memorial Hospital and Dr. Sebastien Monette at The Animal Medical Center helped tremendously with the diagnosis. Dr. Ron Lewis from the Animal Health Centre was there when we needed him most. Dr. Michael Hannigan at Pfizer Animal Health provided maropitant (CereniaTM) for this case.