Abstract
A 5-year-old male slender-tailed meerkat (Suricata suricatta) was diagnosed with squamous cell carcinoma of the left nasal cavity. Computed tomography (CT) scan of the skull to characterize the extent of the neoplasm revealed left nasal cavity involvement with adjacent lysis of the hard palate and left maxillary bone. Localized external radiation beam therapy was scheduled based on guidelines for domestic cats. The meerkat underwent a total of 19 radiation treatments over a 7-week period. During the treatment period, left facial swelling decreased dramatically and quality of life improved. A posttreatment CT scan was performed 8 weeks after the final radiation treatment, which demonstrated reduction in size of the soft tissue mass within the left nasal cavity, however, rostral involvement of the right nasal sinus, increased destruction of left maxillary bone, and extension into the left retrobulbar space with ocular displacement and zygomatic arch destruction were observed. The meerkat began to clinically decline 1 month after the second CT scan and humane euthanasia was elected 6.5 months after initial presentation. Although radiation therapy did not extend survival time as long as was expected, it did result in significant reduction in severity of clinical signs. Treatment had no adverse effects on the meerkat and did not disrupt its dominant social status within the colony.
Case Report
A 5-year-old male slender-tailed meerkat (Suricata suricatta) was diagnosed with squamous cell carcinoma of nasal origin, after a 5-week history of a firm swelling on the left maxilla ventral and rostral to the left eye. Initial clinical signs were attributed to a canine tooth root infection but swelling failed to resolve after removal of the suspected tooth. Initial gingival biopsies did not demonstrate neoplasia, but a second biopsy of the area obtained 5 weeks after initial swelling confirmed a diagnosis of squamous cell carcinoma. The meerkat was determined to be in good health otherwise, based on complete blood count, serum chemistry results, and whole-body survey radiographs. The swelling increased in size during the diagnostic period and began to occlude air flow through the left nostril and compromise vision in the left eye.
Computed tomography (CT) was utilized to better evaluate the extent of the neoplasm. An axial pre- and post-intravenous contrast enhanced CT scan of the skull was performed 2 months after the swelling was first noted (GE HiSpeed Advantage helical CT). A contrast enhancing soft tissue mass filled the entire left nasal sinus. Lysis of the rostral hard palate, left maxillary bone, and squamous portion of the temporal bone was also detected. The nasal mass extended through the region of maxillary bone lysis and was visible as a soft tissue mass on the dorsum of the bridge of the nose. The tumor had not extended through the cribriform plate nor into the retrobulbar space. Localized external beam radiation therapy was scheduled based on guidelines for domestic cats. The meerkat underwent a total of 19 radiation treatments over a 7-week period. To facilitate each treatment, the meerkat was anesthetized using isoflurane chamber induction and maintained on a small face mask. Subcutaneous fluids were administered prior to recovery. Oral medications included doxycycline (Vibramycin calcium syrup, 10 mg/ml, Pfizer, New York, NY, USA; 4.8 mg/kg BID) and meloxicam (Metacam oral suspension, 1.5 mg/ml, Boehringer Ingelheim Vetmedica, Inc., St. Joseph, MO, USA; 0.045 mg/kg every other day). Additionally, topical cyclosporine (Optimmune cyclosporine ophthalmic ointment 0.2%, Schering-Plough Animal Health, Union, NJ, USA) and erythromycin (erythromycin ophthalmic ointment, 5 mg/g, E. Fougera & Co, Melville, NY, USA) were applied to the left eye after each radiation treatment.
During this 2-month period, left facial swelling decreased dramatically, improving air flow through the left nostril and quality of life. The meerkat remained the dominant animal within the colony and was reintroduced to the group after each treatment without incident. Mild left facial swelling and left nasal congestion returned 5 weeks after the final radiation treatment. Weekly nasal flushes with sterile saline reduced the severity of clinical signs. A posttreatment CT scan was performed 8 weeks after the final radiation treatment, which demonstrated some reduction in size of the soft tissue mass within the left nasal cavity. However, rostral involvement of the right nasal sinus, increased destruction of left maxillary bone, and extension into the left retrobulbar space with ocular displacement and zygomatic arch destruction were observed. The meerkat maintained a good appetite and activity level until 1 month after the CT scan, when intermittent open-mouthed breathing was observed, and the left eye was kept closed most of the time. A dramatic clinical decline was observed 3 weeks later, and the meerkat was humanely euthanatized, 6.5 months after initial presentation. Gross findings on necropsy demonstrated that the neoplasia had completely occluded the left nasal cavity and had spread to the right nasal cavity. Neoplastic cells had infiltrated the surrounding mucosa and bony structures, and erosion and fracture of the hard palate was present. There was no neoplasia observed in surrounding lymph nodes or other organs, and other significant findings were restricted to mild chronic interstitial nephritis.
Discussion
Meerkats are in the family Viverridae (subfamily Herpestinae) and are native to the arid regions of southern Africa.8 They are highly social animals that form colonies of up to 30 individuals in the wild.3 The Houston Zoo collection is relatively large by U.S. zoo standards and consisted of 10 male and 10 female meerkats at the time of this case report, with the animal in this report being the dominant male. When evaluating treatment options for this meerkat, there was concern that repeated removal from the colony for radiation treatments would disrupt the animal’s social position or the colony’s social structure in general. Husbandry recommendations for this species stress that even temporary removal of an individual from an established group will be stressful to the individual and may result in permanent rejection from the group.1 Repeated radiation therapy was elected in spite of these concerns and did not result in any social complications. Treatments did not appear to be stressful. The meerkat would enter a kennel voluntarily 3 days per week for transport off grounds to the specialty hospital. When returned to the colony after recovering from anesthesia, the meerkat would quickly assimilate back into the group and maintain its dominant position even through the terminal stages of its disease. The meerkat was also able to help care for its two offspring that were born during the months the animal was receiving radiation therapy. Approximately 1–2 weeks after euthanasia, the social structure of the meerkat colony underwent a significant shift with several weeks of fighting between conspecifics.
Intranasal cancer comprises approximately 1% of all veterinary neoplasms, with carcinomas being the most common form.5 Nasal carcinomas are characterized by progressive local invasion and a low metastatic rate. Prognosis is often poor because bone invasion occurs early in the disease process and surgical excision is often impossible. Radiation therapy with or without surgical debulking is currently the only therapy that has improved survival times in cases of nasal cancer, but squamous cell carcinomas tend to respond less favorably to radiation than sarcomas, adenocarcinomas, or lymphoma. Squamous cell carcinoma associated with the upper canine tooth and maxilla of a domestic ferret (Mustela putorius furo) was treated with a rostral maxillectomy followed by a course of radiation therapy.4 The tumor in this meerkat was located more caudally and, by the time of histologic diagnosis, was not considered surgically resectable.
Diagnosis of squamous cell carcinoma in this case was delayed due to suspicion that the nasal swelling was caused by an infected maxillary canine tooth. Gingival and alveolar biopsy obtained at the time of tooth extraction demonstrated gingival fibrous hyperplasia but did not reveal neoplasia, likely because the tumor was restricted to the nasal cavity at that time. More aggressive biopsies obtained 1 month later confirmed a suspicion of neoplasia, but by that time the swelling had increased in size, no longer making surgical excision with maxillectomy feasible. A similar case occurred in a domestic dog that presented for dental referral when the site of a maxillary canine tooth extraction slowly enlarged over a 6-month period.7 Initial excisional biopsy of the swelling revealed a papilloma with no evidence of neoplasia, but further resection 2 months later diagnosed squamous cell carcinoma. The dog underwent a rostral hemimaxillectomy with clean surgical margins and, though owners declined radiation therapy, was still in remission 5 years later.
Potential side effects of radiation therapy for nasal cancer include rhinitis and mucositis, which commonly resolve within 1–2 months after therapy is completed. Keratoconjunctivitis sicca, corneal ulcers, and cataract formation are possible at higher radiation doses. This meerkat was treated bilaterally with cyclosporine and erythromycin ophthalmic ointment after each radiation treatment in an effort to reduce the risk of secondary ocular abnormalities. On postmortem histologic examination, mild chronic interstitial nephritis was observed, though the meerkat did not demonstrate clinical signs of kidney disease, nor elevation in serum blood urea nitrogen and creatinine. The subclinical nephritis may have been attributed to long-term oral meloxicam therapy.
Although neoplasia has been reported previously in viverrids2 and in a meerkat,6 diagnosis is often made at necropsy or shortly before euthanasia. This is the first report of antemortem diagnosis of neoplasia and attempted treatment in a colony-housed viverrid. It is possible that earlier implementation of radiation therapy may have resulted in a more successful outcome. Although radiation therapy did not extend survival time as long as was expected, it did result in significant reduction in severity of clinical signs and improvement in quality of life. Additionally, multiple anesthetic events and separation from the colony had no adverse effects on the meerkat’s overall condition, appetite, or social status within the colony.
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